Ecohydraulic Modelling of the Crocodile River and the Hartbeespoort Dam

Ecohydraulic modelling of the Crocodile River and the Hartbeespoort Dam

Michael De Clercq

Promotoren: prof. dr. ir. Ronny Verhoeven, prof. dr. ir. Peter Troch Begeleider: dr. ir. Liesbet De Doncker

Masterproef ingediend tot het behalen van de academische graad van Master in de ingenieurswetenschappen: bouwkunde

Vakgroep Civiele techniek Voorzitter: prof. dr. ir. Julien De Rouck Faculteit Ingenieurswetenschappen Academiejaar 2009-2010

Ecohydraulic modelling of the Crocodile River and the Hartbeespoort Dam

Michael De Clercq

Promotoren: prof. dr. ir. Ronny Verhoeven, prof. dr. ir. Peter Troch Begeleider: dr. ir. Liesbet De Doncker

Masterproef ingediend tot het behalen van de academische graad van Master in de ingenieurswetenschappen: bouwkunde

Vakgroep Civiele techniek Voorzitter: prof. dr. ir. Julien De Rouck Faculteit Ingenieurswetenschappen Academiejaar 2009-2010 VOORWOORD EN DANKWOORD ii

Voorwoord en dankwoord

Deze scriptie, gemaakt gedurende het tweede masterjaar Burgerlijk Ingenieur Bouwkunde, gaat over de waterbeheersing in Zuid- Afrika. Ze is gebaseerd op datacollectie, analyse en verwerking. Ze moet het sluitstuk vormen van de boeiende opleiding.

Het kunnen beschikken over zuiver water, vormt een van de grootste uitdagingen van deze eeuw. Watervervuiling, verwoestijning en een stijgend waterverbruik door mens, landbouw en industrie zijn slechts enkele van de redenen waarom een eﬃci¨ent en globaal beheer van deze schaarse, onontbeerlijke grondstof noodzakelijk is. Een integraal waterbeleid is hierin de eerste stap. Ik ben ervan overtuigd dat Zuid-Afrika een land is met enorme mogelijkheden, te danken aan zijn ligging, klimaat, bodemrijkdom, natuur, geschiedenis, bevolking,. . .

Het is echter een land dat zijn kansen niet ten volle kan benutten. De instabiele politieke situatie zorgt voor een enorme ”braindrain”. Zuidelijk Afrika is een regio die in volle expansie is, en meer en meer een Westerse levenswijze aanneemt.

Deze manier van leven heeft een enorme impact op waterverbruik en -vervuiling. Daarom moet waterbeheer met de hoogste spoed bovenaan de agenda geplaatst worden. Toegang tot proper water is immers een mensenrecht. Het is een eerste stap om uit de neerwaartse spiraal te geraken, die leidt tot ziekte en armoede. Niet alleen voor de mens, maar ook voor de ontwikkeling van landbouw en industrie is het schaarse water van kapitaal belang.

Tijdens mijn verblijf in Zuid-Afrika werd ik gefascineerd door de immense natuurrijkdom. De milieuproblematiek, en in het bijzonder de vervuiling van de rivieren, heeft dan ook onmiskenbaar zijn weerslag op fauna en flora. Wil men de biodiversiteit bewaren, dan zal een globale aanpak onontbeerlijk zijn. Ik ben fier dat ik hieraan een klein steentje kan bijdragen. De Hartbeespoort Dam en Krokodilrivier zijn sterk aangetast door eutrofiëring, veroorzaakt door menselijke activiteit. Het streven naar herstel van het natuurlijk evenwicht in dit lokaal ecosysteem, waar zowel mens, dier als plant baat bij hebben, dringt zich op. Een eerste belangrijke stap in dit proces is het in kaart brengen van het probleem door middel van een eco- hydraulisch model. Mijn interesse in de materie alleen, volstond niet om dit werk tot een goed einde te brengen. Heel veel mensen hebben, elk op hun manier, hun steentje bijgedragen om dit eindresultaat te bereiken. Mensen, die mij in de loop der jaren gesteund hebben en mij gemaakt hebben tot wie ik nu ben.

Deze thesis is dan ook de ideale weg om iedereen te bedanken die al die jaren met mij op pad gegaan is. In de eerste plaats zijn dat mijn ouders, die me steunden en aanspoorden om na de studie Master in de Industri¨ele wetenschappen en Technologie, de Master in de Ingenieurswetenschappen aan te vatten en tot een goed einde te brengen.

Speciale dank gaat naar Prof.Dr.Ir. Ronny Verhoeven voor het overdragen van zijn on- metelijke wetenschappelijke kennis en visie, en het eindeloze enthousiasme waarmee hij zijn thesisstudenten voortstuwt.

Uiteraard bedank ik ook alle ander medewerkers van het Laboratorium voor Hydraulica, in het bijzonder Prof.Dr.Ir. Peter Troch, Dr.Ir. Liesbet De Doncker en Ir. Dieter Meire. Hun kennis over de materie was voor deze thesis onontbeerlijk. Ook mijn oprechte dank aan mede- thesisstudenten en mede- ”STRIVEers” Jan Putteman, Bert Schepens, Bruno Vandamme, Steven Langenaken, Niels Vanmassenhove en Jens Van De Maele. Veel van mijn problemen vonden door hun aanstekelijk werkende creativiteit, inspiratie, talent en gedrevenheid, een oplossing.

Deze thesis kon ik slechts realiseren dankzij de actieve medewerking van de betrokken partij- en in Zuid- Afrika. In de eerste plaats denk ik hierbij aan Johan en Annette Wentzel. Hun logistieke steun vormde het draagvlak voor een boeiend verblijf in Zuid- Afrika. Ze hebben mij tevens ingewijd in de lokale cultuur, leefgewoonten en problemen van dit uitgestrekte land.

Frikkie Botha heeft me van in het begin begeesterd met zijn positieve energie en enorme kennis over het probleem. Dank Frikkie.

De benodigde data en informatie kreeg ik van de mensen van het ”Department of Water and Forest” en de ”Water Research Commission”, in het bijzonder mevr. Sibanyoni Francinah die voor de hydraulische data zorgde, mevr. Nicolene Furie die voor de geograﬁsche data zorgde en dhr. Petrus Venter, voorzitter van het ”HBPD Remediation Program”. Aan al die Suid-Afrikaanse vriende, baie dankie!

Deze thesis werd mede mogelijk gemaakt door FETWater, het kaderprogramma voor onderzoek, onderwijs en opleiding in de watersector in SADC- regio(Southern Africa Deve- lopment Community Region). Het programma kwam tot stand door een overeenkomst tussen het Zuid-Afrikaanse Ministerie van Water en Bosbouw (Department of Water Af- fairs and Forestry- DWAF) en de Vlaamse Overheid. Het stelt zich tot doel het creëren van netwerken ter ondersteuning van kennis en opleiding. FETWater wordt gefinancierd door de Vlaamse Regering, de DWAF en de UNESCO. Door hun financiële bijdrage was het voor mij mogelijk om het probleem ter plaatse te gaan bestuderen.

Ook de steun van mijn trouwe vrienden Jeroen Degryse, Michiel Deruyter, Stijn Leuridan en Tom Coghe is heel belangrijk geweest. Ze hebben me steeds tot betere prestaties aangemoedigd. Uiteraard ook speciale dank aan alle andere vrienden en vriendinnen die de afgelopen jaren mijn fantastische studententijd mee hielpen kleuren.

Last but not least bedank ik mijn hele familie: in de eerste plaats mijn ouders, die al 23 jaar al mijn ondernemingen ten volle steunen, maar ook mijn grootouders die steeds enthousiast in mijn plannen meegaan. Ook dank aan mijn broer en zus, die ik een boeiende toekomst wens.

Bedankt voor alles!

Michael De Clercq, May 30, 2010 PREFACE AND ACKNOWLEDGMENTS v

Preface and acknowledgments

This master thesis, made during the ﬁnal year of the Master in Civil Engineering, is dealing about the integrated water control in South Africa. The availability of clean water for everyone is one of the main challenges of this century. South Africa is a region in full expansion, adapting a more and more Western way of living. This way of living has an enormous impact on water use and water pollution.

During my stay in South Africa, I was fascinated by the immense natural resources. The environmental problems, especially the pollution of the rivers, has an undeniable impact on the fauna and ﬂora.

One of the problems linked with this challenge is the severe eutrophication problem of the Crocodile River and Hartbeespoort Dam, caused by human activities. Aiming the recovery of the natural equilibrium in this local ecosystem, in which as well humankind, animals as plants benefit, is necessary. A first important step in this process is to map out the problem by means of an ecohydraulic model. Purpose of this model is to find a solution in which all stakeholders can get on with.

This master thesis is the ideal way to thank people you always wanted to thank. First of all my parents, who stimulated and supported me to study civil engineering. Without them, I would never have reached this realization.

Special thanks goes to Prof.Dr.Ir. Ronny Verhoeven for imparting all the scientiﬁc knowledge, his vision and endless enthusiasm, driving along his thesis students. Of course, I like to thank all the other co- workers of the Laboratory for Hydraulics, in particular Prof.Dr.Ir. Peter Troch, Dr.Ir. Liesbeth De Doncker and Ir. Dieter Meire. Their knowledge about this matter was indispensable for my thesis. Also my sincere thanks to all the co- students which also used the ”STRIVE”- software. The intense cooperation helped me to solve a lot of my problems. Their creativity, inspiration, talent and passion proves infectious.

This master thesis could only be realised thanks to the active support of all the involved parties in South Africa. In the first place, I would like to mention the assistance of Johan and Annette Wentzel. Their logistic and moral support was the base for a fascinating and unforgettable stay in South Africa. They introduced me to the local culture, way of living and problems of this vast country. Frikkie Botha has rapped me from the beginning with his positive energy and immoderate knowledge about the problem. Thank you Frikkie. The required data and information was provided by the co-workers of the ”Department of Water and Forest” and the ”Water Research Commission”. Particularly from Mrs. Sibanyoni Francinah for the hydraulically data, Mrs. Nicolene Furie for the geometrical data and Mr. Petrus Venter, chairman of the ”HBPD Remediation Program”. Only thanks to the financial support of the UNESCO, this project could be fulfilled. Aanaldie Suid-Afrikaanse vriende, baie dankie!

This thesis was made possible by FETwater, the Framework program for Research, Edu- cation and Training in the Water sector in the Southern Africa Development Community Region. It is a venture based on an agreement between the South African Department of Water Affairs and Forestry (DWAF) and the Flemish government. The program is aimed at the creation of networks to fulfil capacity and training needs. FETWater is funded by the Flemish Government, the DWAF and UNESCO. Through their financial support, it was possible to study the problem on site, and gain essential knowledge that led to what this discourse has become.

Also the support of my loyal friends Jeroen Degryse, Michiel Deruyter, Stijn Leuridan and Tom Coghe has been very important to me. They have always encouraged me to better performances. Obviously also special thanks to all the other friends and girlfriends who helped me for the past years giving colour to my fantastic student time.

Last but not least, I would like to thank my whole family: ﬁrst of all my parents, who support me in all my undertakings, for more than 23 years now. But also my grandparents who went enthusiastically along in all my plans. Also thanks to my brother and sister, which I wish a fascinating future.

Thanks for everything! Michael De Clercq, May 30, 2010 DANKWOORD (AFRIKAANS) vii

Dankwoord (Afrikaans)

Ek wil graag hiermee my opregte dank betuig aan al die mense wat my op die een of ander manier gehelp het tydens my verblyf in September 2009 in Hartbeespoort. Eerstens en veral dank ek Dr. Johan Wentzel en sy vrou Annette vir hul veelsydige steun. Dit het die grondslag gevorm van ’n boeiend verblyf in Suid-Afrika. Hulle het my ingewy in die plaaslike kultuur, leefgewoontes en probleme van hierdie uitgestrekte land. Frikkie Botha het my die weggewys in die ingewikkelde probleme wat die HBPD ervaar. Sy groot belangstelling en kennis oor die ekologiese en bestuursprobleme van die dam, was baie aansteeklik. Danksy hom is ek in kontak gebring met wetenskaplikes en belanghebbendes wat daagliks in die praktyk met die probleem besig is. Ek dank Petrus Venter, Morn´ede Jager, Johan Mar´e vir die verskaf van data en gedetailleerde inligting in verband met die Hartbeespoort Biological Remediation Program.

Verder dank ek Dr Carin van Ginkel en die mense van die Departement van Waterwese in Pretoria (in die besonder Me. Francinah Sibanyoni) vir die voorsien van meetdata wat onontbeerlik was vir die voltooing van hierdie thesis.

Aan al die mense in Suid-Afrika wat my gehelp het, ook aan diegene wat ek nie hierbo vermeld het nie, ontvang my hartlike dank!

Michael De Clercq, May 30, 2010 PERMISSION FOR REPRODUCTION viii

Permission for reproduction

”The author gives permission to make this master dissertation available for consultation and to copy parts of this master dissertation for personal use. In the case of any other use, the limitations of the copyright have to be respected, in particular with regard to the obligation to state expressly the source when quoting results from this master dissertation.”

Michael De Clercq, May 30, 2010 Ecohydraulic modelling of the Crocodile River and Hartbeespoort Dam

Michael De Clercq

Master thesis submitted to obtain the academic degree of Master in de Ingenieurswetenschappen Bouwkunde : optie Water- en Transport

Academic year: 2009-2010

Supervisors: Prof. Dr. Ir. R. Verhoeven, Prof. Dr. Ir. P. Troch Scription supervisor: Dr. Ir. L. De Doncker

Faculty of Engineering Ghent University

Department of Structural engineering Chairman: Prof. Dr. Ir. J. De Rouck

Summary

Purpose of the project is to create an ecohydraulic model of a heavily polluted and eutrophicated South African dam and its main tributaries. Hydraulic, physical, chemical and biological parameters will be implemented in a software program, resulting in a model that can be used for simulations. This model can be a good footing to work out possible long- term solutions. This master thesis is the ﬁrst part of this project. An extensive literature study is done about the problem and the possible short and long term solutions. Also, the modelling of the main feeding river is started.

Key words

Ecohydraulics, modelling, Crocodile River, Hartbeespoort Dam Ecohydraulic modelling of the Crocodile River and the Hartbeespoort Dam Michael De Clercq Supervisor(s): Ronny Verhoeven, Peter Troch, Liesbet De Doncker, Dieter Meire

Abstract— This article deals about the modelling of the Hartbeespoort during the summer months (see ﬁgure 1), form the actual prob- Dam and Crocodile River (South Africa). This dam suffers a major eu- lem. The sustained dominance of cyanobacteria, produces user- trophication problem. An ecohydraulic model should contribute to work out solutions for this problem. As ﬁrst part of this, the problem has been related problems that include tastes and odours in potable wa- mapped out and the hydraulic modelling of the Crocodile river started. ters produced from the dam, impaired recreational and aesthetic Keywords— Ecohydraulics, modelling, Crocodile River, Hartbeespoort uses, and decrease revenue from impoundment-related commer- Dam, Hartbeespoortdam cial activities and residential sales.

I. INTRODUCTION HE Hartbeespoort Dam, situated in the Crocodile (West) TMarico catchment, is one of the most popular tourist destinations in the North West Province. Residential and commercial development in the catchment and specifically around the dam has increased significantly over the last few years placing substantial pressure on the environment. A number of rivers form part of the catchment, namely the Crocodile (90% of the total supply), Hennops, Jukskei, Skeerpoort, Leeuwspruit, Mo- Fig. 1. Accumulating algae and hyacinths in front of the Hartbeespoort Dam hangwe and Magalies Rivers as well as the Swartspruit. wall The soil around Hartbeespoort Dam is suffering more and longer droughts each year. Although this change in climate, continuing agriculture on a certain scale, is primordial for the B. Objective local economy and people. For this agriculture, irrigation is vital. That is why a large amount of water with sufficient quality In the first part, purpose is to make a hydraulic model of the should be collected during the rainy season. Hartbeespoort Dam and its main supplying river, the Crocodile River. This river will be modelled in one dimension, starting II. PROBLEM STATEMENT AND OBJECTIVE from the most upper river flow station, until the discharge in the Hartbeespoort dam. The flow of its three major tributaries will A. Problem Statement be taken into account. In the future (the continuation thesis), During the dry season the water of the dam is more than 50% the dam reservoir will be implemented into a two dimensional treated wastewater from urbanised areas upstream. The ecology model. The reservoir will be fed by the Crocodile River and of Hartbeespoort Dam has been disturbed by a number of fac- two other tributaries. The outflow is simulated by two irrigation tors, such as, increased enrichment due to rising nutrient inflow channels and the continuation of the Crocodile River. from the catchment resulting in unwanted algal blooms, over- In the second part of the modelling, an ecological model is grazing by excessive numbers of undesirable fish species, con- made. An algae growing model and pollution spreading model tinuous water level fluctuations, and the destruction of shoreline will be the main subjects. Also the influence of wetlands will vegetation. These factors have led to the depletion of one of the be discussed. In the end, the purpose is to make a correlation most critical elements in the aquatic food chain, namely zoo- between the hydraulic model ecological model. All this will be plankton. The primary production (algae growth) therefore ex- preceded by an extensive literature study of the problem in all ceeds the grazing potential of the primary consumers of which of its aspects. the zooplankton forms a major component. Excessive plant nutrient loadings, originating largely from III. HYDRAULIC MODEL wastewater treatment works discharges in the catchment area of To built the hydraulic model, the following data is neces- the Crocodile River, have resulted in the dam becoming hyper- sary: discharge data (river gauging stations A2H051, A2H050, trophic. The combination of plant nutrients and biophysical fac- A2H049, A2H045, A2H044, A2H014, A2H012, A2H058, tors have supported the sustained dominance of very dense ag- A2H013, A2H081, A2H082, A2H083), precipitation- and evap- gregations of principally Microcystis aeruginosa, a blue-green oration data, longitudinal data (relief map) and cross- sections. algae (cyanobacteria) within the dam. Uncontrolled and ex- The manning coefficient is the unknown parameter in the model. cessive growth of unwanted biomass, and in this case specifi- With various hydrographs of floodings, a proper manning coef- cally the growth of blue-green alge and water hyacinths mainly ficient is fitted in the model. For the development of the model, the modelling software ”STRIVE” (Stream River Ecosystem) is dam and allow sediments to settle in this small impoundment. It used. It is build in the ”Femme”- environment (Flexible envi- will also enable dredging of phosphate loaded sediments in the ronment for mathematically modelling). impoundment or allow the phosphates to be removed by means The STRIVE- model exists of different modules, of which of chemical dosing. Figure 2 shows the principle of it. the most important is the hydraulic model. It concerns a onedi- mensional hydrodynamic model that allows to model non- per- manent stream. The 1D- model is based on the Saint- Venant- equitations, which consist of the continuity equitation and the momentum equitation. For solving this set of non- linear differential equations, the help of the Preissmann schema and the Double Sweep algorithm is used. Also a module which describes the transport of solved particles and substances and re- action processes of the present vegetation, is provided.

IV. ECOLOGICAL MODEL Fig. 2. Principle of a pre- impoundment The study of the ecological problems forms the basis for the future ecological model. The dam has a hypertrophic status, which means the aquatic ecosystem is associated with very high VI. CONCLUSION nutrient concentrations where plant growth is determined by physical factors. The water quality problems are serious and The Hartbeespoort Dam is a dam with a huge economical, almost continuous. social and ecological value. For years, it has been degenerated, The presence of an algal bloom, existing of cyanobacteria, but the last ten years, active work to rehabilitate the area has forms the largest treads. These cyanobacteria spread cyanotox- been done. An effective reservoir management programme for ins, which are harmful for humans and animals. Upstream, an Hartbeespoort Dam is set up, based upon the recommendations effective tackling of the point- sources is needed. In the dam of the HBPD Remediation Program. It will ensure clean water and river bed, biological remediation under the form of wetlands for human and environmental health. The HBPD Remediation and shoreline restoration is the best option. By this method, the Program could be an example to other polluted catchments in phosphorus concentration in the dam will be lowered in a natural the country. way. To stop the algal blooms, a growth limiting factor should What could be concluded from the preparations of the eco- be determined. This could be light, carbon dioxide, nitrogen or logical model, is that, if phosphorus is to be made the growth phosphorus. limiting requirement, the present average phosphorus concentration of more than 343 μg/l (2004) should be reduced by V. S OLUTIONS more than 80%, to bring the phosphorus concentration in the 30 to 50 μg/l range required. Nevertheless, from the differ- The HBPD Remediation Program worked out a program of ent algal growth limiting requirements available, the reduction ”Water Quality Management” The overall aim is to reduce ex- of phosphorus concentration seems to be the most practical of ternal pollution by 60% from the current levels, which requires all. Only by reaching this objective, the ultimate goal to change managing several pollution sources simultaneously as described the trophic status of the dam from hypertrophic to mesotrophic, below. It is clear that most of the attention should go to the will be reached. Most attainable solution for the moment is the reducing of the phosphorus concentration. construction of a pre- impoundment, supplemented with some In the short- term, one of the most important things to do is short- term actions such as chemical water treatment and sed- to make people aware of the problem and convince them that iment removal. However the ecological modelling itself is not everybody could contribute to solve the problem. Recreation started yet, in the future, it will definitely contribute to the devel- regulations and public awareness and education are main things opment of the existing solutions and open doors for new ideas the people can play a role in. The Hartbeespoort Remediation and opportunities. Program has already set up some effective, short- term solutions: The aim of the thesis was two folded: map out the problem • Fishery management and monitoring by means of an extensive literature study and field visit, fol- • Control and algae removal lowed by starting the hydraulic model (basis of the ecohydraulic • Control hyacinths (harvesting and composting) model). This thesis should form a broad base for further re- • Sediment removal (contain lots of nutrients) search and model development. The data collection, informa- • Chemical fixing of the phosphorus in the Crocodile River tion and contact persons should simplify future work around this Some long- term solutions could be: subject. The now developed hydraulic model needs certainly • Replacing phosphate in detergents further optimization. Especially more intense study of the lon- • Stricter phosphorus standard for treated sewage water gitudinal section will precise the present results. Even though • Pre- impoundment it took lots of time, resulting in very few results, the STRIVE- The most attainable solution is the pre- impoundment. The pur- package has a great potential for bringing in new perceptions. pose of it is to limit the buildup of phosphates in the dam which is fed from water in the Crocodile River (90% of the water supply). It will attenuate water in the river before flowing into the NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xii

Nederlandse samenvatting - Summary in Dutch

Inleiding

Vandaag vormt het beschikken over water ´e´en van de belangrijkste uitdagingen van de 21e eeuw. In verschillende regio’s in de wereld daalt de hoeveelheid jaarlijkse neerslag. Grote gebieden verdorren. Zo ook het noord- westelijke deel van Zuid- Afrika. Om aan de grote vraag naar water te voldoen en het probleem van de onregelmatige aanvoer te omzeilen, werd een groot aantal kunstmatige dammen gebouwd op de Zuid- Afrikaanse rivieren. De aldus ontstane reservoirs vangen momenteel meer dan 50% van de totale gemiddelde jaarlijkse waterafvoer op.

Gebrek aan water is één van de beperkende factoren bij de ontwikkeling van de North West Province. Grondwater en oppervlaktewater staan onder zware druk door de grote vraag vanuit de (mijn)industrie, landbouw en de verstedelijkte gebieden. Het is cruciaal voor het welzijn en de ontwikkeling van de provincie, dat een goed watermanagement programma van kracht wordt. Vervuiling van grond- en oppervlaktewater zijn zeer gevaarlijk voor de mens, en fauna en flora. Remediering brengt enorme kosten met zich mee.

De North West Province kent een droog tot half- droog klimaat met onregelmatige neer- slaghoeveelheden. Er zijn in deze provincie nauwelijks natuurlijke meren, net als in de rest van Zuid- Afrika. Daarom werden de laatste honderd jaar heel wat kunstmatige reser- NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xiii voirs aangelegd, als voorziening van drinkbaar water, voor irrigatie en recreatie. Ook het visbestand is van groot belang: het zorgt voor voedsel en werkgelegenheid.

Er zijn in totaal 28 grote dammen in de North West Province, met een waterkwaliteit die varieert van gemiddeld tot zeer slecht. Eén van de meest vervuilde is de Hartbeespoort Dam. Een uitgebreid onderzoek naar de mogelijkheden tot rehabilitatie ervan, werd recen- telijk afgewerkt. Veel ervaringen en resultaten werden dan ook gebruikt voor deze thesis. Ze vormen een uniek vertrekpunt voor de rehabilitatie van andere dammen in Zuid- Afrika, vooral voor dammen die hetzelfde probleem kennen als de HBPD: eutrofiëring ten gevolge van overmatige aanwezigheid van nutriënten.

Met deze thesis wil de auteur bijdragen aan het rehabilitatieproces van de HBPD en zijn belangrijkste aanvoerrivier, de Krokodilrivier. Dit zal gebeuren door het uitwerken van een eco- hydraulisch model van de rivier en de dam. In eerste fase wordt de Krokodilrivier gemodelleerd.

De bodem rond de Hartbeespoort Dam wordt elk jaar droger en droger. Ondanks de verdorring, blijft landbouw ´e´en van de meest belangrijke sectoren van de locale economie. Bijgevolg is een degelijk irrigatiesysteem onontbeerlijk. Daarom is het van groot belang om tijdens het regenseizoen voldoende water van goede kwaliteit te kunnen bergen.

De HBPD, gelegen in het Crocodile (West) Marico stroombekken, is één van de populairste toeristische bestemmingen in North West Province. Residentiële en commerciële ontwikkeling in het bekken en vooral rond de dam, hebben er de laatste jaren voor gezorgd dat de druk op het milieu toeneemt. Gedurende het droge seizoen bestaat meer dan de helft van het aangevoerde rivierwater uit afvalwater. De Krokodilrivier zorgt voor 90% van de aanvoer. Hij voert het vervuilde water af vanuit de stroomopwaarts gelegen geürbaniseerde gebieden rond Johannesburg en Pretoria. De ecologie van de HBPD werd door verschillende factoren verstoord: woekering van algen, ten gevolge van de grote hoeveelheid nu- triënten, tal van vreemde, ongewenste vissoorten, grote schommelingen in het waterpeil en de vernietiging van de oevervegetatie. NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xiv

Deze factoren hebben geleid tot de verdwijning van één van de meest onontbeerlijke elemen- ten in de aquatische voedselketen: het zooplankton. De primaire productie (algengroei) zal daardoor het grazende potentieel van de primaire verbruikers, zoals zooplankton, overtre- ffen.

De contaminatie met onder andere fosfor, stikstof en sulfaten, zorgt ervoor dat het water niet meer onmiddellijk bruikbaar is voor de stroomafwaarts gelegen landbouwgebieden. In de dam zelf ontwikkelde zich daardoor ook een eutroﬁ¨eringprobleem.

Om een oplossing voor het probleem uit te werken, hebben we in eerste instantie een degelijk waterstromings- en uitwisselingsmodel nodig. De thesis start met een historische en geograﬁsche schets van de HBPD. De functies worden besproken in 1.4, gevolgd door een uitgebreide probleemschets en doelstelling in 2.1. In het derde deel wordt het hydraulisch model besproken, inclusief de theoretische achtergrond en de uitleg over de gebruikte mo- delleringssoftware. Het vierde hoofdstuk omvat de literatuurstudie over de ecologisch problemen. Deze dient als basis voor de latere ecologische modellering. In hoofdstuk vijf worden enkele korte- en langetermijn oplossingen van naderbij bekeken.

In het kader van deze thesis, werd gedurende één maand ter plaatse onderzoek verricht. Een uitgebreid verslag hiervan is terug te vinden in bijlage G. Alle gebruikte data, informatie, literatuur, figuren, foto’s en de digitale versie van deze thesis zijn terug te vinden op de bijgevoegde CD.

De regio kwam in volle expansie in het midden van de 19e eeuw, toen er grote hoeveelheden goud werden gevonden. De populatie in de regio groeide erg snel. Om in het nodige voedsel te kunnen voorzien, nam ook de landbouw een enorme sprong. In 1902 werden de eerste plannen gemaakt om een dam te bouwen in Hartbeespoort. Het duurde echter tot 1923 eer de dam in zijn huidige vorm tot stand kwam. Vanaf het begin van de 20e eeuw werden irrigatiekanalen aangelegd, die vandaag in het totaal meer dan 532 km lang zijn. De dam zelf is een boogvormige muur met vari¨erende straal, afgesteund op de rotswanden van het Magaliesgebergte. In 1971 werden overloopstuwen ge¨ınstalleerd, waardoor een totale NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xv capaciteit van 205 miljoen m3 werd bereikt. Het stuwmeer heeft een oppervlakte van 2062 ha en de omtrek bedraagt 56 km. Uit de dam vertrekken twee irrigatiekanalen (Oost- en Westkanaal) die zich in het achterliggende landbouw- en mijngebied rond Brits verder vertakken.

De belangrijkste functies van de dam zijn, naast irrigatie (80%), productie van drinkwater en de controle van vloedgolven. De volledige regio van Madibeng hangt voor zijn productie van drinkwater af van de dam. De regio is ook heel belangrijk voor het toerisme. Heel wat inwoners van de steden Johannesburg en Pretoria, hebben er vakantie- en weekendverblij- ven. De HBPD is het grootste reservoir in de regio, en allerhande watersporten (zeilen, waterski, vissen) zijn er erg populair.

Probleemschets en doelstelling

De slechte waterkwaliteit heeft op vele manieren een negatieve impact op het leven in de regio. De grootste moeilijkheid vormen de vele factoren waarover geen controle mogelijk is.

Hieronder zijn beknopt de grootste problemen weergegeven.

• Door de wasgolven tijdens het regenseizoen (zomer) worden telkens grote hoeveelheden afval meegesleurd met de rivier. De hoeveelheid meegespoeld afval en con- taminaties kan oplopen tot vijf keer de normale waarde. De vervuiling bestaat uit menselijk afval, afval afkomstig uit storten en een overmaat aan meststoﬀen die van de akkers wegspoelt.

Een ander probleem vormen de waterzuiveringstations. Deze zijn niet voorzien op grote aanvoer en gaan al snel over tot gewone overstort. Het eﬄuent voldoet ook niet aan de vooropgestelde norm inzake fosforconcentratie. Bovendien is er onge- controleerde uitbreiding van de sloppenwijken, zonder enige vorm van riolering of waterzuivering. NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xvi

• De combinatie van het hoge gehalte aan nutriënten, intense zonnestraling, lage wind- snelheden en warm water, zijn de ideale omgevingfactoren voor de groei van drijvende blauw- groene algen. De HBPD is zeer ge-eutrofiëerd door de enorme aanvoer van nutriënten. Elke dag verlaat ongeveer 620 miljoen liter effluent de waterzuiveringsstations in de omgeving van Johannesburg en Pretoria, om via de Krokodilrivier en zijn bijrivieren naar de stuwdam te vloeien. Daar komt het water tot stilstand, waarna de schadelijke algen zich kunnen ontwikkelen. Het probleem van de verstikkende algenbloei bestaat al sinds de jaren ’70 van vorige eeuw. Gedurende vele jaren focuste de rehabilitatie zich op de controle van aanvoer van fosfaten bij puntbronnen, terwijl nu meer en meer de nadruk zal worden gelegd op de biologische remediëring.

• De blauw- groene algen bestaan uit cyanobacteriën. Ze zorgen voor verstopping van filters in waterzuiveringsstations die instaan voor de productie van drinkwater en irrigatiewater. Bovendien kunnen ze gifstoffen loslaten (cyanotoxins) die zorgen voor een onaangename geur, smaak en kleur. Wanneer deze gifstoffen in het drinkwater terecht komen, kunnen ze bij mens en dier ernstige aandoeningen veroorzaken (vooral leveraantasting en chronische ziekten) en ook contact met de huid (zwemmen) kan ernstige gevolgen hebben. De hoeveelheid vergif in het water van de HBPD is vaak zo hoog, dat volgens de WHO alle gebruik van het water, alsook zwemmen en beoefenen van watersporten, zou moeten verboden worden.

• Sedimentatie zorgt voor twee problemen: het reduceert de capaciteit van de dam en het houdt vervuiling vast. Momenteel is de capaciteit van het stuwmeer 20% lager dan bij opening van de dam. Historische en hedendaagse vervuiling zit in het sediment, dat constant omgewoeld wordt door boten en vissen. Daardoor is er voortdurend een bijkomende aanvoer van de nutri¨enten koolstof, stikstof en fosfor, wat voor een extra verstoring van het evenwicht zorgt. Naar schatting 30 tot 40 miljoen kubieke meter sediment zou zich sinds opening in 1923 al verzameld hebben in de dam.

• Als gevolg van de grote urbanisatie en industri¨ele uitbreiding, is de hoeveelheid NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xvii

beschikbaar grondwater, dat algemeen van goede kwaliteit is, aanzienlijk gedaald. Ook dat heeft een grote weerslag op de biodiversiteit in de regio.

Al deze problemen zorgen voor extra kosten voor waterzuivering. Bovendien daalt de interesse van de toeristische sector (minder tewerkstelling, minder inkomsten), en daalt de waarde van de eigendommen. Een gebrek aan water vormt een rem op de ontwikkeling van de locale economie in al haar aspecten.

Doel van het project is een eco- hydraulisch model ontwerpen van de dam en zijn aan- voerrivieren. Dit model integreert de instroom- en de oeverecologie, en houdt rekening met fysische aspecten als stroming, waterhoogte, sedimenten, etc. Hiervoor wordt het softwarepakket ”STRIVE” (= STream RIVer Ecosystem) gebruikt. Na een uitgebreide literatuurstudie over de ecologische en hydraulische problemen, volgt het creëren van een hydraulisch model van de belangrijkste toevoerrivier, de Krokodilrivier. Dit model is 1D en wordt verder behandeld in het hoofdstuk ”Hydraulic model”. In een volgende fase van het project zal de dam hydraulisch gemodelleerd worden (2D) en zal een ecologisch model uitgewerkt worden. Uiteindelijk doel is om deze twee modellen (hydraulisch en ecologisch) aan elkaar te gaan linken. Met het bekomen model kunnen dan verschillende lange termijn scenario’s gesimuleerd worden, met als doel te gaan uitzoeken op welke manier het eutrofiëringsprobleem het best kan opgelost worden. Het zou moeten bijdragen om toekomstige ontwikkelingen te voorspellen, kritische punten te traceren en prioriteiten toe te kennen.

Hydraulisch model

Voor het ontwikkelen van het model werd gebruik gemaakt van ’STRIVE’ (STream RIVer Ecosystem). Dit model is uitgebouwd binnen de ’Femme’ omgeving. ’Femme’ is een mo- delleeromgeving geschikt voor ontwikkeling en toepassing van ecologische, tijdsafhankelijke processen. Het STRIVE- model bestaat uit verschillende modules waarbij de hydraulische NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xviii module de belangrijkste is. Het betreft een 1D hydrodynamisch model dat toelaat niet permanente stroming te modelleren. Het 1D model is gebaseerd op de Saint- Venant vergelijkingen, welke bestaan uit de continu¨ıteitsvergelijking en de bewegingsvergelijking. De oplossing van deze set niet-lineaire diﬀerentiaalvergelijkingen gebeurt met behulp van het Preissmann schema en het Double Sweep algoritme. Verder bestaat er ook een module die het transport van opgeloste stoﬀen en deeltjes en de reactieprocessen van de aanwezige vegetatie beschrijft. In deze thesis wordt vooral aandacht besteed aan de transportmodule. Deze module zal gebruikt worden bij de ecologische modellering van de dam en rivier.

Om het model te kalibreren en te valideren is een uitgebreide gamma aan gegevens verzameld. De belangrijkste hierbij zijn de debietdata van de vier meetstations op de bovenloop van de Krokodilrivier. De hydrogrammen van deze meetstations zullen de basis vormen voor de ijking van het model, en moeten helpen bij het bepalen van een mannincoëfficiënt voor elke sectie. Hieronder volgt een overzicht van de verzamelde informatie die van belang is voor de hydraulische modellering.

• Debietmetingen van stations: A2H051, A2H050, A2H049, A2H045, A2H044, A2H014, A2H012, A2H058, A2H013, A2H081, A2H082, A2H083 (zie ﬁguur 3.2).

• Neerslag- en verdampings- data

• Dwarsdoorsneden (enkel ter hoogte van de meetstations en enkele in de dam)

• Langsdoorsnede (beperkt)

Alle gebruikte data zijn terug te vinden op de bijgevoegde CD. Bijlage D bevat een overzicht.

De beperkte informatie omtrent de dwars- en langsdoorsneden zorgde voor heel wat moei- lijkheden. In werkelijkheid bestaat de bovenloop van de Krokodilrivier uit een groot aantal panden met een subkritische stroming (te berekenen met STRIVE), met daartussen enkele stroomversnellingen, watervallen en afdammingen waar superkritische stroming heerst. NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xix

Deze laatste is niet te berekenen met STRIVE. Door het gebrek aan gedetailleerde geometrische data kon echter alleen met een gemiddelde helling tussen de gekende dwarssecties gerekend worden. Deze dwarssecties zijn enkel gekend in de omgeving van de overlaten, waardoor de helling ertussen als bijna constant werd beschouwd. Hierdoor naderde de gebruikte helling echter een kritiek punt, waardoor in combinatie met de vrij grote dwarssecties en lage debieten, al snel superkritische stroming optrad. De grote helling beperkte de mogelijkheden van het model enorm, waardoor in de toekomst verdere optimalisatie van het hydraulisch model zal nodig zijn. Meer gedetailleerde geometrische data zullen nodig zijn om de superkritische secties te kunnen elimineren en zo een realistischer beeld te kunnen vormen van de mannincoëfficiënt. Deze laatste ligt door hierboven vermelde problemen telkens aan de hoge kant.

Ecologisch model

In hoofdstuk vier wordt uitgebreid ingegaan op de ecologische problemen in het bekken van de bovenloop van de Krokodil Rivier en de HBPD. Deze studie moet een basis vormen voor het latere ecologische modelleringswerk.

Het grote probleem in de dam is eutrofiering. De algemene oorzaken hiervan werden reeds in hoofdstuk twee behandeld. In dit hoofdstuk wordt dieper ingegaan op enkele specifieke aspecten. Eutrofiering is het proces van overvloedige verrijking van water met nutriënten, dat typisch resulteert in problemen gelinkt aan macrofyten, algen en/of cyanobacteriën. Een meer kan zich in vier verschillende trofische toestanden bevinden:

• Oligotroof: weinig nutri¨enten, en dus een beperkte aquatische levensvormen.

• Mesotroof: een gemiddelde hoeveelheid nutri¨enten, met beginnende problemen met de waterkwaliteit.

• Eutroof: rijk aan nutri¨enten, zeer productief aquatisch milieu voor dier en plant, meer en meer problemen met de waterkwaliteit. NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xx

• Hypertroof: zeer rijk aan nutri¨enten, zeer productief aquatisch milieu voor dier en plant, dat enkel beperkt wordt door fysische factoren. Continu ernstige problemen met de waterkwaliteit.

De Hartbeespoortdam bevindt zich in deze laatste categorie. Bedoeling is om op termijn een mesotrofe toestand voor deze dam te bereiken. De aanwezigheid van de algenbloei, en de daaruit volgende cyanobacteriën- populatie vormt de grootste bedreiging. Daarom moet dit probleem prioriteit krijgen. Alleen door het wegnemen van één van de noodzakelijke voedingsfactoren, zal de groei ervan kunnen ingeperkt worden. Het drastisch beperken van de beschikbare hoeveelheid fosfor zal hierin een cruciale rol spelen. Specifieke maatregelen, zoals het verwijderen van sedimenten, aanpak van (punt)bronnen en behandeling van het aanwezige water moeten hiervoor zorgen. Vooral via de biologische weg zijn er tal van mogelijkheden, zoals het gebruik van (water)planten die de fosfor opnemen en de groei van zooplankton stimuleren. Het herstellen van de oevervegetatie, zal erosie tegengaan en reeds dichter bij de bron een bepaalde vorm van zuivering bewerkstelligen.

De problemen in de dam moeten uiteraard in eerste instantie zoveel mogelijk bij de bron aangepakt worden. In paragraaf 4.3 is een uitgebreide studie weergegeven van de ecostatus van de verschillende toevoerrivieren van de dam. Behalve de Skeerpoort rivier, hebben alle rivieren de ecostatus ’zwak’. De kwaliteit van het ecosysteem van deze rivieren, moet dus drastisch verbeteren. Vooral het aanleggen en herstellen van de oevervegetatie en het aanleggen van wetlands langs en op deze rivieren, kan hiervoor zorgen.

Ook in de dam zelf zal de herstelling van de oevervegetatie en het aanbrengen van drijvende wetlands een positieve invloed hebben. De planten zorgen voor opname van nutri¨enten en bieden daarnaast tal van andere voordelen. Verder moet er management en monitoring van de huidige vispopulatie gebeuren. Veel van de aanwezige vissoorten zijn exoten, die een verstoring van het ecologisch evenwicht veroorzaken. Tevens brengen ze door het omwoelen van de bodem, extra nutri¨enten in het water. NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xxi

Alle data die benodigd zijn voor het opstellen van het ecologisch model, zijn terug te vinden op de CD. In bijlage D is hiervan een overzicht weergegeven.

Oplossingen

Het HBPD Remediation Program heeft een programma omtrent ”Water Quality Manage- ment” ontwikkeld. Het uiteindelijke doel is om een reductie van de externe pollutie van 60% van het huidige level te bereiken. Zoals in 4.2.8 wordt uitgelegd, moet de meeste aandacht gaan naar de reductie van de fosforconcentratie.

Op korte termijn is ´e´en van de belangrijkste opdrachten de bewustmaking van de bevolking en de sensibilisering om individueel bij te dragen waar mogelijk. Tevens moet een regel- geving uitgewerkt voor de recreatiesector, en moet voorzien worden in degelijke opleiding in verband met deze materie.

Belangrijke kortetermijnoplossingen zijn:

• Monitoring en Management van het visbestand

• Controle en verwijdering van algen

• Controle van de waterhyacinten (oogsten en composteren)

• Het verwijderen van sedimenten

• Chemische binding van het fosfor in de Krokodilrivier

Langetermijnoplossingen zijn:

• Vervangen van fosfaten in detergenten

• Strengere fosfornormen voor het eﬄuent van rioolwaterzuiveringsstations

• Pre- impoundment (bijlage F) NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xxii

Conclusies

De Hartbeespoort Dam is een dam met een enorme economische, maatschappelijke en ecologische waarde. Na jaren van verwaarlozing, wordt sinds de laatste tien jaar actief gewerkt om het gebied te rehabiliteren. Een eﬀectief waterbeheersingsprogramma van het Hartbeespoort Dam reservoir is opgestart, gebaseerd op de aanbevelingen van de HBPD Remediation Program. Het beoogt proper water voor mens en milieu. Het HBPD Reme- diation Program kan als voorbeeld gesteld worden voor andere vervuilde stroomgebieden in het land.

Uit hoofdstuk vier, het ecologisch model, kan geconcludeerd worden dat, als men resultaat wil boeken door beperking van fosfor, de huidige gemiddelde fosforconcentratie van meer dan 343 μg/l (2004) moet dalen met meer dan 80%, tot 30a50 ` μg/l. Dit is enorm, maar desalniettemin de meest haalbare procedure om algengroei te beperken. Alleen door het halen van deze doelstelling, kan de status van de dam veranderen van hypertroof naar mesotroof. Meest voor de hand liggend op dit moment, is de bouw van een pre- impound- ment, aangevuld met enkele korte termijn oplossingen, zoals chemische behandeling van het water en verwijdering van het sediment.

Hoewel met de ecologische modellering zelf nog niet is begonnen, zal ze in de toekomst zeker kunnen bijdragen om de bestaande oplossingen te optimaliseren, en zal ze de aanzet vormen voor nieuwe idee¨en en opportuniteiten.

Het doel van dit proefschrift is tweeledig: het in kaart brengen van het probleem door middel van een uitgebreide literatuurstudie en een bezoek ter plaatse, gevolgd door het starten van het hydraulisch model, als basis voor het eco- hydraulisch model.

Dit proefschrift moet een brede basis vormen voor verder onderzoek en ontwikkeling van het model. Het verzamelen van gegevens, informatie en contacten (zie bijlage G) moet de toekomstige werkzaamheden rond dit onderwerp vereenvoudigen. NEDERLANDSE SAMENVATTING - SUMMARY IN DUTCH xxiii

Het huidig ontwikkelde hydraulisch model moet zeker verder geoptimaliseerd worden. Vooral een meer intensieve studie van de langsdoorsnede moet de nauwkeurigheid van de huidige resultaten verder verhogen. Hoewel er veel tijd werd ingestopt, zijn de resultaten tot nu toe beperkt. Toch heeft het STRIVE- pakket een groot potentieel voor het aanbrengen van nieuwe inzichten.

Hoewel nog veel water door de Krokodilrivier en de dam zal stromen vooraleer het probleem volledig zal opgelost zijn, zijn de vooruitzichten veelbelovend. . . CONTENTS xxiv

Contents

Voorwoord en dankwoord ii

Preface and acknowledgments v

Dankwoord (Afrikaans) vii

Permission for reproduction viii

Overview ix

Extended abstract x

Nederlandse samenvatting - Summary in Dutch xii

Table of contents xxiv

Abbreviations xxvii

Glossary xxviii

List of Figures xxxii

List of Tables xxxv

1 Introduction 1 1.1 Crocodile (West) Marico Water Management Area ...... 4 1.2Historyofthedam...... 10 1.3Characteristicsofthedam...... 14 1.4Functionsofthedam...... 16 1.4.1 Irrigation...... 16 1.4.2 Industry and mining ...... 16 1.4.3 Recreation...... 16 1.4.4 Productionofdomesticdrinkingwater...... 18 CONTENTS xxv

1.5 References ...... 18

2 Problem Statement and Objective 21 2.1ProblemStatement...... 21 2.1.1 Waste...... 21 2.1.2 Eutrophication ...... 22 2.1.3 Erosion and sediments ...... 27 2.1.4 Groundwater ...... 28 2.1.5 Agriculture...... 29 2.1.6 Domestic consumption ...... 29 2.1.7 Developments...... 29 2.1.8 Conclusions...... 29 2.2 Objective of the master thesis ...... 30 2.2.1 Hydraulic model ...... 30 2.2.2 Ecologicalmodel...... 30 2.3 References ...... 31

3 Hydraulic modelling 34 3.1Collecteddata...... 34 3.1.1 FlowData...... 34 3.1.2 EvaporationData...... 35 3.1.3 Rainfalldata...... 37 3.1.4 Cross sections ...... 39 3.1.5 Longitudinal sections ...... 39 3.2Model...... 40 3.2.1 Backgroundinformation...... 40 3.2.2 Crocodile River ...... 46 3.2.3 Hartbeespoort Dam reservoir ...... 60 3.3 References ...... 61

4 Ecological model 63 4.1Thermalstratiﬁcationindams...... 64 4.2 Trophic status ...... 65 4.2.1 Hypertrophic dam ...... 72 4.2.2 Algalbloom...... 72 4.2.3 Cyanobacteria...... 74 4.2.4 Growthrequirementsofalgae(andhyacinths)...... 76 4.2.5 Light as a growth limiting requirement ...... 77 4.2.6 Carbon dioxide as growth limiting requirement ...... 77 4.2.7 Nitrogenasagrowthlimitingrequirement...... 78 CONTENTS xxvi

4.2.8 Phosphorus as growth limiting requirement ...... 78 4.3 Ecological status of the Upper Crocodile Catchment ...... 81 4.3.1 Crocodile River ...... 84 4.3.2 Dambasin:HBPDRemediationProgram...... 93 4.4Model...... 105 4.5 References ...... 105

5 Solutions 109 5.1Short-termsolutions...... 110 5.1.1 Fisherymanagementandmonitoring...... 111 5.1.2 Controlandalgaeremoval...... 111 5.1.3 Controlhyacinths(harvestingandcomposting)...... 111 5.1.4 Sediment removal ...... 111 5.1.5 Chemical ﬁxing of the phosphorus in the Crocodile River ...... 117 5.1.6 Others...... 117 5.2Long-termsolutions...... 118 5.2.1 Replacingphosphateindetergents...... 118 5.2.2 Stricterphosphorusstandardfortreatedsewagewater...... 118 5.2.3 Pre- impoundment ...... 118 5.3Conclusion...... 120 5.4 References ...... 120

6 Conclusions 122

A Ecostatus of the Crocodile (West) Marico WMA 124

B Sectoral Water Requirements 126

C Land Use 128

D CD- Content 130

E Model of the dam 132

F Pre- impoundment concept 134

G Report Unesco 142 ABBREVIATIONS xxvii

Abbreviations

AFW Artificial Wetlands a.s.l. above sea level CR Crocodile River CSIR Council for Scientific and Industrial Research DACET Department of Agriculture, Conservation, Environment and Tourism DEM Digital Elevation Model DS Dry solid DWAF Department of Water Affairs and Forest FRD Foundation for Research Development FSL Full supply level HBPD Hartbeespoort Dam HWAG Hartbeespoort Water Action Group IWQS Institute for Water Quality Studies MAR Mean Annual Runoff NWP North West Province RFS River Flow Station RSA Republic of South Africa WMA Water Management Area WRC Water Research Commission GLOSSARY xxviii

Glossary

Algae. Chlorophyll-bearing organisms in the plant subkingdom Thallobionta. They may be free-ﬂoating or attached to structures such as rocks or other submerged surfaces.

Anaerobic. A condition in which no dissolved oxygen is present.

Anthropogenic. Resulting from the pressure of human activities.

Biodiversity. Biodiversity comprises composition, structure, and function of ecosystems. Composition is the identity and variety of elements in a collection, and includes species lists and measures of species diversity and genetic diversity. Structure is the physical organization or pattern of a system, from habitat complexity as measured within communities to the pattern of patches and other elements at a landscape scale. Function involves ecological and evolutionary processes, including gene ﬂow, disturbances, and nutrient cycling.

Biota. Animal and plant life characteristic of a given region.

Bloom. A noticeable change in colour of water caused by excessive algal growth.

Blue-green algae.SeeCyanobacteria.

Catchment. The area that receives the rain that ﬂows into a particular watercourse.

Chlorophyll. The green pigment found in plants responsible for photosynthesis.

Cultural Eutrophication. Eutrophication resulting from human (anthropogenic) activities (such as excessive use of fertilisers and/or detergents).

Cyanobacteria. A large group of bacteria comprising unicellular and multicellular proka- ryotes that use photosynthesis as their principal mode of energy metabolism. Also referred to as blue-green algae. GLOSSARY xxix

Cyanotoxins. Toxic substances (including cyclic peptides, alkaloids and lipopolysaccha- rides) produced by cyanobacteria as secondary metabolites.

Dam. 1. A barrier constructed to obstruct the ﬂow of a watercourse and store water. 2. The water stored by the structure.

Destratiﬁcation. The development of complete vertical mixing within a lake or reservoir that either partially or totally eliminates separate layers of temperature, plant or animal life.

Diffuse-source Pollution. Pollution that comes from a wide area that is not easily quantifiable, such as fertilisers draining off farmlands or pollutants in the runoff from urban areas. Opposite of point-source.

Ecological Integrity. The ability of an ecosystem to support and maintain a balanced, integrated composition of physico-chemical habitat characteristics, as well as biotic components, on a temporal and spatial scale, that are comparable to the natural state (i.e. unimpaired) characteristics of such an ecosystem. (High ecological integrity implies that the structure and functioning of an ecosystem are unimpaired by anthropogenic stresses.)

Ecosystem. The total community of living organisms and their associated physical and chemical environment.

Epilimnion. The upper level of water in a thermally stratiﬁed water body of relatively warm water in which mixing occurs as a result of wind action and convection currents. (Cf. Hypolimnion.)

Eutrophic. A state of an aquatic ecosystem rich in nutrients, very productive in terms of aquatic animal and plant life and exhibiting increasing signs of water quality problems.

Eutrophication. The process of nutrient enrichment of waters that results in problems associated with macrophyte, algal or cyanobacterial growth. See Cultural Eutrophica- tion.

Hypertrophic. A state of an aquatic ecosystem associated with very high nutrient concentrations where plant growth is determined by physical factors. Water quality problems are serious and almost continuous.

Hypolimnion. The lower level of water in a thermally stratiﬁed water body, characterised GLOSSARY xxx by a uniform temperature that is colder than that of other strata in the water body. (Cf. Epilimnion.)

Impoundment. The water body formed behind a weir or dam wall, which can be used for irrigation, ﬂood control, domestic or industrial use etc.

Macrophyte. A plant large enough to be seen by the naked eye, especially one associated with an aquatic habitat.

Mesotrophic. A state of an aquatic ecosystem with intermediate levels of nutrients, fairly productive in terms of aquatic animal and plant life and showing emerging signs of water quality problems.

Microcystins. Cyclic peptide cyanotoxins produced by some cyanobacteria.

Natural Eutrophication. Eutrophication resulting from natural processes (like nutrient enrichment from the local geology and soils).

Non-point Source Pollution. Pollution that comes from a diffuse source, such as runoff from a large agricultural area, that is usually difficult to quantify.

Nutrient. Substance that supports growth and reproduction. In the context of aquatic plants, these include nitrogen, phosphorus, carbon, silica and iron (among others).

Oligotrophic. A state of an aquatic ecosystem low in nutrients and not productive in terms of aquatic animal and plant life.

3− Orthophosphate. The chemical species PO4 in all the forms in which it binds to other chemical constituents. These can be inside solid particles, adsorbed on their surfaces or dissolved in water. When dissolved, this form of the nutrient phosphorus is readily available for use by plants.

Phytoplankton. See Plankton.

Plankton. The large community of microorganisms that ﬂoats freely in the surface waters of oceans, seas, rivers and lakes. They are moved passively by wind, water currents, or waves, having little or no powers of locomotion themselves. The plant plankton (phytoplankton) includes many microscopic algae, particularly the diatoms. They form the basis of the food chain in water, being eaten by the animal plankton (zooplankton), which in turn provides food for ﬁsh. GLOSSARY xxxi

Point-source Pollution. Pollution that comes from a single source that is usually easily quantiﬁable e.g. sewage works or factory.

Riparian. Living or located on the banks of streams and rivers.

Runoff. Water that does not filter into soil but flows over the surface and into natural surface waters.

Sedimentation. The process by which suspended solids settle downwards.

Stratiﬁcation. The formation of separate layers (for example, of temperature, plant or animal life) in a lake or reservoir.

Surface Water. Water above the ground surface in impoundments, lakes, dams and rivers.

Suspended Solids. Inorganic or organic matter, such as clay, minerals, decay products and living organisms, that remains in suspension in water. In surface waters it is usually associated with erosion or runoﬀ after rainfall events.

Total Phosphorus. The sum of phosphorus occurring in particulate matter and soluble (dissolved) orthophosphate.

Trophic Status. The degree of nutrient enrichment and of the associated eutrophication problems of an aquatic ecosystem.

Turbidity. A measure of the light-scattering ability of water. It indicates the concentration of suspended solids in the water.

Water Management Area. An area established as a management unit in the national water resource strategy within which a catchment management agency will conduct the protection, use, development, conservation, management and control of water resources.

Wetland. Land which is transitional between terrestrial and aquatic systems where the water table is usually at or near the surface, or the land is periodically covered with shallow water, and which land in normal circumstances supports or would support vegetation typically adapted to life in saturated soil.

Zooplankton. See Plankton. LIST OF FIGURES xxxii

List of Figures

1.1 Hartbeespoort Dam - North West Province - South Africa ...... 3 1.2 Hartbeespoort Dam rear side ...... 4 1.3 Crocodile (West) Marico Water Management Area (source: DWAF) .... 7 1.4 Location of the Hartbeespoort Dam and Crocodile River (source: Google Maps)...... 8 1.5 Map of Hartbeespoort Dam and its main supplying rivers (source: Google Earth)...... 9 1.6Damwallandarch...... 12 1.7Daminformation...... 12 1.8Thedamduringtheconstruction(source:DWAFwebsite)...... 13 1.9 Construction plan - cross- section (source: DWAF website) ...... 13 1.10Theeastirrigationcanalnearthedam...... 14 1.11 Dam spillway ...... 15 1.12Damwallandoutﬂowsystems...... 17 1.13IrrigationintheareaofHBPD...... 17 1.14 Transvaal Yacht Club at Cosmos (Hartbeespoort) ...... 18

2.1Litteraccumulationinthedam...... 22 2.2 Point discharges in the Upper Crocodile WMA ...... 23 2.3 Seven of the nine hypertrophic dams in RSA are located in the Crocodile Maricocatchment...... 24 2.4Algaeaccumulationnearthedam...... 25 2.5 Sediment zones in the impoundment ...... 27 2.6 Sediment cross- section near the dam wall ...... 28

3.1Flow-level-correlationforweirA2H050...... 35 3.2 Overview of the hydraulic scheme of the Crocodile River and HBPD .... 36 3.3Averagemonthlyevaporation...... 37 LIST OF FIGURES xxxiii

3.4Dailyevaporation...... 37 3.5Averagemonthlyrainfall...... 38 3.6Dailyrainfall...... 38 3.7 Longitudinal section of the total Crocodile River ...... 39 3.8FlowchartofStrive(afterK.Buis)...... 41 3.9ConceptualmodelofaSouthAfricanRiver(source:WRC)...... 42 3.10 Hydrograph in two sections (I and II) of the river, with indication of time shift and peak ﬂattening ...... 43 3.11 Longitudinal section of the CR, based on the availlable data ...... 47 3.12 River section A (source: Google Earth) ...... 48 3.13 The Crocodile River in section A ...... 49 3.14Floodpeak6,withn=0.2...... 50 3.15Floodpeak9,withn=0.16...... 50 3.16 River section B (source: Google Earth) ...... 52 3.17Flow-level-correlationforweirA2H045...... 52 3.18Floodpeak11,withn=0.18...... 53 3.19 River section C (source: Google Earth) ...... 55 3.20Flow-level-correlationforweirA2H012...... 56 3.21 A2H012: weir on the Crocodile River at kalkheuwel ...... 58 3.22 River section D (source: Google Earth) ...... 58 3.23 Drop of river section D, based on the available data ...... 59 3.24 Flood wave on section D ...... 60 3.25ViewontheCR,justbeforethemouthintheHBPD...... 60

4.1Theenvironmentalwaterbalance(source:WRC)...... 63 4.2 Conceptual depth/length profile of a dam during thermal stratification . . 64 4.3 Simplified schematic illustration of the most important factors driving the eutrophication process...... 66 4.4 Chlorophyll-a distribution in the dam: the red zones are the high concentrations,thegreenzonesthelower...... 68 4.6 Potential general negative impacts of eutrophication ...... 68 4.5 Current situation and target for the trophic status of the HBPD ...... 69 4.7 Schematic illustration of some specific impacts of eutrophication ...... 70 4.8Nitrogen-cycle...... 73 4.9 Algal bloom during the summer of 2008 ...... 74 4.10 Algal distribution visible on satellite pictures ...... 74 LIST OF FIGURES xxxiv

4.11Cyanobacteria...... 75 4.12 Hartbeespoort Dam total phosphate mass ...... 80 4.13 Habitat integrity and the biological response indicators ...... 81 4.14 Symbols representing the six indicators ...... 82 4.15 Ecological status of the Upper Crocodile Catchment ...... 83 4.16TheJukskeiRivernearVlakfontein...... 88 4.17RietvleiriverjustpasttheRietvleiDam...... 90 4.18 The Magalies River in the Magelies Nature Reserve ...... 92 4.19StatusoftheHBPDshoreline...... 96 4.20Transitional/bufferzonebetweenlandandwater...... 96 4.21 Improved/artificially enhanced shoreline conditions ...... 98 4.22 Small bay at the Caribbean Beach Club golf course in 2005 (up) and 2008 (below)...... 99 4.23Floatingwetlandsfoodweb...... 100 4.24 Wetlands planned around the dam (source: Google Earth and HBPD Re- mediationProject)...... 101 4.25FloatingwetlandsontheHBPD...... 102 4.26 Catfish (left) and carp (right) should be targeted as part of the fisheries management...... 103

5.1OverviewoftheHBPDRemediationProgram...... 109 5.2Massivegrowthofhyacinths...... 112 5.3Harvestinghyacinths...... 112 5.4Compostingthehyacinths...... 112 5.5 Major sediment zones in the dam reservoir ...... 114 5.6 Loads of the sediment ...... 115 5.7 Near the conﬂuence of the CR and the HBPD, a lot of sedimentation occurs 116

F.1 In- and off-line flow equalization ...... 138 F.2 Usual pre- impoundment ...... 138 F.3 Pre-impoundment with flow diversion ...... 139 LIST OF TABLES xxxv

List of Tables

1.1Damcharacteristics...... 15

3.1CharacteristicsofSectionA ...... 47 3.2 Cross sections section A ...... 48 3.3CharacteristicsofSectionB ...... 51 3.4 Cross sections Section B ...... 51 3.5CharacteristicsofSectionC ...... 54 3.6 Cross sections Section C ...... 54 3.7CharacteristicsofSectionD ...... 57 3.8 Cross sections section D ...... 57

4.1 Relationships between trophic status and monitoring variables...... 67 4.2 HBPD current trophic status: hypertrophic ...... 67 4.3Theriverhealthcategories...... 83

5.1AlternativesfortheHBPD...... 110 5.3 Sediment contents ...... 117

F.1 Long- term water budget for Hartbeespoort Dam (1964-1978) ...... 136 F.2 Percent P load reduction for diﬀerent fractions soluble P in outﬂow during therainyseason...... 140 INTRODUCTION 1

Chapter 1

Introduction

Today, water is one of the most important challenges of the 21st century. In several regions of the world, rainfall is decreasing annually. New arid areas originate and others are extending. One of those is the northwestern region of South Africa. The large demands for water, and the erratic flow of most South African rivers, have led to the creation of artificial lakes, i.e. impoundments on all the major rivers, in order to stabilize flow and therefore guarantee annual water supply. The total capacity of state impoundments amounts to more than 50% of South Africa’s total average annual river runoff. As South Africa is a semi-arid country where, in many areas, the available water resources within the river basins are unable to supply the rapidly increasing local water requirements. As the number and size of inter-basin transfers increases, more detailed water resource analysis and planning studies are being undertaken in both the donor and recipient basins.

Water is a key limiting factor of development in the North West province. Groundwater and surface waters are under heavy user pressures from mining, industry, settlements and agriculture. It is crucial, for the well being and development of the province, that good water management practices are promptly adopted. Exhaustion and pollution of ground- and surfacewater is highly costly to remediate and the associated problems may cause even large communities to collapse. The puriﬁcation of polluted surface water, hazardous both to humans and animals, are also very costly. The North West Province is characterized by dry to semi dry climate with erratic rainfalls. There are no natural lakes in the province as in the rest of South Africa and most rivers are seasonal. Certain areas have currently fairly good groundwater resources to meet the local needs. The reservoirs of dams are another vital source of potable water, irrigation and recreation in the province. The ﬁsh stocks have also considerable potential for food production and job creation. There are INTRODUCTION 2

28 large dams and hundreds of small farm dams in the North West. The water quality in most of the larger dams varies from moderate to bad. One of the most polluted dams is the Hartbeespoort Dam (HBPD - figure 1.1 and 1.2). Extensive investigation into the possibilities of rehabilitating the most important dam in the North West has been recently finalized. The results and experiences of this study, together with the action plan, are summerized in this thesis. They provide a unique contribution and point of departure also for rehabilitating other dams in South Africa. Particularly dams suffering from eutrophication (indicated by increased nutrient levels and algal blooms) share the problems of Hartbeespoort Dam. With this master thesis, the author wants to contribute in the rehabilitation process of the Hartbeespoort Dam, by modelling the dam and its most important feeding river.

The soil around Hartbeespoort Dam is suﬀering more and longer droughts each year. Although this change in climate, continuing agriculture on a certain scale, is primordial for the local economy and people. For this agriculture, irrigation is vital. That is why a large amount of water with suﬃcient quality should be collected during the rainy season. In South Africa, dams play a very important role in collecting and catching this water. As mentioned, the water should meet a certain standard of quality to be used for irrigating crops and plants.

Hartbeespoort Dam, situated in the Crocodile (West) Marico catchment, is one of the most popular tourist destinations in the North West Province. Residential and commercial development in the catchment and specifically around the dam has increased significantly over the last few years placing substantial pressure on the environment. A number of rivers form part of the catchment, namely the Crocodile, Hennops, Jukskei, Skeerpoort, Leeuwspruit, Mohangwe and Magalies Rivers as well as the Swartspruit. During the dry season the water of the dam is more than 50% treated wastewater from urbanised areas upstream. The ecology of Hartbeespoort Dam has been disturbed by a number of factors, such as, increased enrichment due to rising nutrient inflow from the catchment resulting in unwanted algal blooms, overgrazing by excessive numbers of undesirable fish species, continuous water level fluctuations, and the destruction of shoreline vegetation. These factors have led to the depletion of one of the most critical elements in the aquatic food chain, namely zooplankton. The primary production (algae growth) therefore exceeds the grazing potential of the primary consumers of which the zooplankton forms a major component.

The Crocodile River, the main feeding river of the Hartbeespoort Dam (roughly 90%), leads INTRODUCTION 3 down the water from the upwards situated urbanised area of Johannesburg and Pretoria (4100 km2), where to many contaminations enter the river. This results in the fact that the water of the Hartbeespoort Dam is so much loaded with contaminations (phosphorus, sulphite and nitrogen) that it is not directly usable anymore for the irrigation of the downward lying agricultural land. In the dam itself, a giant eutrophication problem has been developing.

That is the reason why a model of the dam will be worked out in order to look for possible scenarios to solve the problem of eutrophication as accurate as possible. For this purpose, in ﬁrst instance a reliable water discharge and exchange model is needed. This dissertation starts with an outline of the historical and geographical situation of the dam. The functions of the dam will be discussed in 1.4. Then an extensive formulation of the problem will be worked out in 2.1. Also, the exact objective of this master thesis will be highlighted (2.2). In the third part of this thesis, the hydraulic model will be discussed in detail, including the theoretical background and information about the used modelling software. The fourth section includes the literature study on the ecological problems, forming the basis for further ecohydraulic modelling. In chapter ﬁve, short and long term solutions are discussed.

This master thesis also included a one month ﬁeld trip to HBPD. A detailed report of this can be found in annex G. All the used data, information, literature, ﬁgures, pictures and a digital version of this thesis can be obtained from the CD, included at the back of this book. The exact content of the CD is written down in annex D.

Figure 1.1: Hartbeespoort Dam - North West Province - South Africa 1.1 Crocodile (West) Marico Water Management Area 4

Figure 1.2: Hartbeespoort Dam rear side

1.1 Crocodile (West) Marico Water Management Area

The Hartbeespoort Dam Reservoir (also known in the local language as Harties) is a dam situated on the border between the North West Province and the Gauteng province of South Africa (ﬁgure 1.4). It makes part of the Local Municipality of Madibeng, and is lying in a valley to the south of the Magaliesberg mountain range and north of the Witwatersberg mountain range, about 35 kilometers west of Pretoria, the capital of the RSA. The name of the dam means ”pass of the hartbees” (a species of antilope) in Afrikaans. The dam was originally designed for irrigation which is currently its primary use.

The town of Hartbeespoort is situated close to the dam wall and the villages of Kosmos, Melodie, Ifaﬁ and Meerhof can be found alongside its banks. Hartbeespoort was previously known as Schoemansville, after General Hendrik Schoeman.

The dam is fed by several rivers. The Magalies River and the Crocodile river are the main feeding rivers (ﬁgure 1.5). The smaller tributaries are the Leeuwen and the Swartspruit. Most of them have a negligible ﬂow, but are transporting non- negligible amounts of pollution and contaminations. This counts especially for the Hennops and Jukskei rivers. The main supplying river, the Crocodile River, springs in the northwest part of Johannesburg. It is one of the main tributaries of the Limpopo River.

The Crocodile River makes part of the Crocodile (West) Marico Water Management Area (WMA) ( ﬁgure 1.3). It is situated primarily within the North West Province with parts of 1.1 Crocodile (West) Marico Water Management Area 5 it in the northern region of Gauteng and the southwestern corner of the Limpopo Province. Along the northwest side, the WMA borders on Botswana.

The Crocodile and Marico rivers are the two main rivers in this WMA, which at their confluence forms the Limpopo River that flows eastwards to the Indian Ocean. The Limpopo River is an international river that is shared by Botswana, Zimbabwe and Mozambique. The headwaters of the west flowing Molopo River, a tributary of the Orange River, also formspartoftheWMA.

Important features in this WMA include the large dams such as Hartbeespoort, Rooikopjes, Vaalkop, Roodeplaat, Klipvoor and Molatedi. The natural mean annual runoff (MAR) of the Crocodile (West) Marico WMA is 855 million m3 per annum. Approximately 75% of the total surface runoff from the WMA flows down the Crocodile River, while the Marico catchment contributes 20% and the Upper Molopo catchment 5%. More than half of the total water use in the WMA comprises urban, industrial and mining use, approximately a third is used by irrigation and the remainder of the water requirements are for rural water supplies and power generation (see annex B). These water requirements are far more than what can be provided by the current water resources. In order to meet the current demand, much of the water in the WMA is being imported mainly from the Vaal River system for domestic and industrial use purposes.

Land-use in the south-eastern portion of the WMA is dominated by the urban areas of northern Johannesburg, Midrand and the areas under the jurisdiction of the City of Tshwane Metropolitan Council (Pretoria) (see annex C). Small holdings and commercial agricultural activities (limited to formal irrigation) take place in the area north west of Jo- hannesburg, but south of the Magaliesberg mountain range. Irrigation occurs mostly in the Crocodile catchment especially immediately downstream of Hartbeespoort Dam but also further downstream, south of Thabazimbi as well as along the mainstem of the Crocodile River. A very wide variety of crops are produced, ranging from intensive vegetable production to tobacco, maize, cotton, citrus and subtropical fruits, sorghum, sunflowers and soya bean. A significant amount of irrigation also takes place near Mafikeng, situated in the Molopo catchment with water sourced from the Grootfontein dolomitic compart- ments. Dry land crops (usually maize) are grown in the south and south-eastern parts of the WMA where the rainfall is higher, while in the drier northern and western regions, land-use consists mostly of stock and game farming. Further away from the main river channels, most of the land-use is small-scale irrigation from farm dams as well as the raising of small and large livestock and game animals. Extensive mining activities occur north 1.1 Crocodile (West) Marico Water Management Area 6 and east of Rustenburg. These mines are mainly focused on the platina group of metals which are in great demand on the world market at the moment, as well as granite mining. The Madibeng Municipal is considered one of the fastest growing economical regions in Africa because of the platinum mining operations. Mining is tending to out-perform the agriculture sector. The area is the world’s third largest chrome producer and includes the richest platinum reserve (situated on the Merensky Reef).In the Upper Crocodile River sub-catchment, small open-cast stone and sand quarries are common as well as a number of large platinum and chrome mines. Limited mining occurs in the rest of the WMA.

The Crocodile (West) Marico WMA is the second most populous water management area in the country. In 2001, the population of this WMA has been estimated to be 6.7 million people. Approximately 85% of the population in the WMA live in the urban metropolitan area of Johannesburg and Pretoria, situated in the Upper Crocodile and Apies / Pienaars sub-catchments where they are attracted by the economic activity and employment opportunities in the region. Extensive informal settlements have as a result, sprung up around the periphery of the major urban centres. The number and density of population declines with increasing distance from these upper reaches and the rural population is more evenly distributed than the urban population.

Economic activity in the WMA is dominated by the urban and industrial complexes of northern Johannesburg and Pretoria and platinum mining northeast of Rustenburg. About 25% of the Gross Domestic Product of South Africa originates from the Crocodile (West) Marico WMA. Mining is an important and stable sector of the regional economy that provides strong employment opportunities.

An important feature with regards to the water resourses in the Crocodile (West) Marico WMA, are the large dolomitic aquifers which occur along most of the southern part of the Water Management Area from Pretoria to Mafikeng. Large quantities of water are abstracted from these aquifers, mainly for urban and irrigation use, while a significant portion of the base flow of several rivers originates as springs from these aquifers. Along the lower Crocodile River, sandy aquifers are found from which large quantities of water are abstracted for irrigation purposes. The remainder of the WMA is mostly underlain by fractured rock aquifers, which are well utilised for rural water supplies.

The Crocodile (West) Marico water management area is divided into six sub-areas by the Department of Water Aﬀairs and Forestry for water resources planning purposes. In this master thesis, most of the attention will go to the Upper Crocodile sub-management area. 1.1 Crocodile (West) Marico Water Management Area 7

This area corresponds to the catchment of the Crocodile River upstream of the HBPD, which includes the major tributaries of the Sterkstroom, Magalies, Bloubankspruit, Jukskei and Hennops rivers. The Crocodile River has its source in the Witwatersrand mountain range at a height of 1 700 m.a.s.l. The northern suburbs of Johannesburg, as well as parts of adjacent cities such as Kempton Park and Krugersdorp are situated in this sub-catchment. There are two large dams in this sub-catchment, namely Hartbeespoort and Roodekopjes. The upper reaches of the catchment are densely settled.

Figure 1.3: Crocodile (West) Marico Water Management Area (source: DWAF) 1.1 Crocodile (West) Marico Water Management Area 8

Figure 1.4: Location of the Hartbeespoort Dam and Crocodile River (source: Google Maps) 1.1 Crocodile (West) Marico Water Management Area 9

Figure 1.5: Map of Hartbeespoort Dam and its main supplying rivers (source: Google Earth) 1.2 History of the dam 10

1.2 History of the dam

The possibility of building a dam in the Hartbeespoort, where the Crocodile River cuts through the Magaliesberg, had already been considered since 1902 although the water of the Crocodile River has been used since the Stone Age. For nine hundred years the Iron Age people utilized the clay, iron ore and ﬂora for man and animal. In 1836 the white pioneers discovered the potential of the water. Fountains, brooks and rivers were harnessed for household and agricultural purposes and for mechanical power for mills. Fords and bridges were constructed and the rivers became the focal point of attention.

In those years already water was gathered from rivers and brooks and taken to the nearby fertile grounds by furrows. Sometimes small weirs were built in the streams and often retention dams were constructed in convenient positions to regulate the supply of water over dry periods. In the Brits and De Kroon area there were seven unlined furrows and weirs in the Crocodile River alone before 1863 which irrigated about 2000 ha of riverside land. These ’old furrows’ were operated and maintained by owners until recently. Between 1850 and 1900, lots of gold mines were discovered in the region, resulting in a booming demographical and economical expansion.

In 1898 Hendrik Schoeman built the ﬁrst ’large scale’ dam of stone and cement and dammed the whole Crocodile River. In those years it was the biggest dam in the southern hemi- sphere. The dam was of concrete, and was about nine meters high. This dam did not impound any water, but was used for the leading out of water and the irrigation of adjacent land. Unfortunately the engineer made a mistake in his calculations and the dam was washed away in a ﬂood. Johan Schoeman, Hendrik Schoeman’s son, in 1902 revived the idea by rebuilding the furrows fed by a smaller weir higher up in the river. With this he irrigated 3000 ha of land.

Between 1905 and 1910, various preliminary investigations were undertaken by the then Department of Irrigation of the Republic of the Transvaal. With the establishment of the Union of South Africa in 1910, the investigations were temporarily suspended. However increased public interest resulted in the Hartbeespoort Irrigation Scheme (Crocodile River) Act (Act 32 of 1914). Act 32 of 1914 authorised the construction of the Hartbeespoort Dam on the farm Hartbeesfontein. Construction of the dam was however postponed due the outbreak of the First World War (1914 - 1918).

Building of the dam started in 1918 when ground was bought or expropriated, roads, a 1.2 History of the dam 11 suspension footbridge with a span of 60 m, staff quarters, offices, power house, cement shed were built. Work also started on the building of the two cofferdams to dam up the river so that the dam wall foundations could be poured. These cofferdams however washed away during the flood of March 1921.

After the ﬂood the department employed the engineer who revised the plans by replacing the gravity structure with a varying radius arch structure, which would be supported against the rock faces on both sides of the Poort. This was done primarily to be able to complete the foundations and get the dam level above riverbed in one dry season and also to save costs on the volume of cement required. Initial estimates were that 800 000 bags of cement would be required but by changing the design of the wall this amount was reduced to 250 000 bags. The coﬀerdams were reinforced in April 1921 but still more water that could be handled by pumps moved through the working areas. It was then decided to divert the river through an 80 m long tunnel with dimensions of 1,8 x 3,6 m. The water was guided into the tunnel from a weir upstream. The river was successfully diverted through the tunnel on 24 May 1921 making it possible for the foundations to be excavated.

The first concrete was poured into the foundations of the wall by 29 July 1921 and by 7 September 1921, 7220 m3 of concrete had been placed, raising the wall 2 m above the riverbed (figure 1.8 and 1.9. The floods of the 1922 -1923 season were impounded and the wall proper completed in April 1923. The road over the wall, now the new main road between Pretoria and Rustenburg, was opened to the public in September 1923. The dam overflowed for the first time in 1925. After completion, 97 farmers and 65 lessees made use of the water from the Hartbeespoort Dam. The west end of the dam wall sports an unusual feature, an arch built as a replica of the Arc de Triomphe (figure ). There are two inscriptions on the arch. The inscription on the eastern side reads ’Dedi in deserto aquas, flumina in invio’, which means ’I give waters in the wilderness and rivers in the desert’. The inscription on the western side reads ’Sine aqua arida ac misera agri cultura’, which means ’Without water it is arid and miserable in agriculture’.

One of the main aims of the Hartbeespoort Irrigation Scheme was to provide employment to soldiers demobilized after World War One as well as poor whites. However, it is reported that the attitude of these groups towards hard labor resulted in a request for permission to use blacks, which was granted in 1919. At the peak of construction, some 1835 men were employed at the dam. In 1964, the Department of Water Aﬀairs proposed that the dam be raised to increase its capacity and to make a larger volume of water available for irrigation purposes. The raising of the dam was done by means of ten 2,74 m radial crest 1.2 History of the dam 12 sluices on the spillway raising the full supply level by 2,4 m. Today, the dam still irrigates almost 14000 ha of farmland (ﬁgure 1.7).

Figure 1.6: Dam wall and arch

Figure 1.7: Dam information

One of the main aims of the Hartbeespoort Irrigation Scheme was to provide employment 1.2 History of the dam 13 to soldiers demobilized after World War One as well as poor whites. However, it is reported that the attitude of these groups towards hard labor resulted in a request for permission to use blacks, which was granted in 1919. At the peak of construction, some 1835 men were employed at the dam.

In 1964, the Department of Water Aﬀairs proposed that the dam be raised to increase its capacity and to make a larger volume of water available for irrigation purposes. The raising of the dam was done by means of ten 2,74 m radial crest sluices on the spillway raising the full supply level by 2,4 m. Today, the dam still irrigates almost 14000 ha of farmland.

Figure 1.8: The dam during the construction (source: DWAF website)

Figure 1.9: Construction plan - cross- section (source: DWAF website) 1.3 Characteristics of the dam 14

1.3 Characteristics of the dam

The dam covers approximately 20 square kilometres, with a mean depth of 9,6 meters and maximum depth of 45,1 meters (depending on sedimentation). It’s normal range of annual water level fluctuation adds up to 0,8 meters. It has a capacity of 205 million m3 and a shoreline of about 56 km when full. The dam reservoir receives water from 4 112 km2 area from Johannesburg via the Jukskei and Hennops River that flow into the Crocodile River. Roughly 80% of the water is used for irrigation with lesser uses for domestic consumption and compensation flows. Madibeng Local Municipality depend totally on the irrigation water from HBDP. All inhabitants around the dam and large settlements downstream, including the town of Brits, use purified dam water for drinking.

The dam wall is 149,5 meters long and 59,4 meters high and is built across a gorge cutting through the Magaliesberg. The dam has a variable radius arch wall of containing 68 000 m3 of mass concrete.It has a side channel spillway on its left flank. Two outlets, one on each bank, provides water to a irrigational canal system which stretches 64 km along both sides of the Crocodile River Valley. The east canal (figures 1.10 and 1.12)is 48 km long and the west canal 56 km long. Both canals have a carrying capacity of 8,5 m3/s. The north canal, an extension of the east canal, is 30 km long. The total length of the branch canals is 532 km. In 1970 the dam supply level was raised by 2,44 m by the installation of ten crest gates on the spillway (figure 1.11), enlarging the capacity of the dam to 205 million m3. Each crest gate is 10,06 m long and 2,44 m high. It has a total capacity of 2322 m3/s. During periods of heavy rain, the spillsways are used to regulate the level of the dam. Table 1.1 gives an overview of the dam characteristics.

Figure 1.10: The east irrigation canal near the dam 1.3 Characteristics of the dam 15

Figure 1.11: Dam spillway

Dam wall Length 100,6 m Width (at base) 22 m Height 59,43 m Crest level 1167 m High flood level 1165 m Crest width 4,6 m Full supply level (post 1971) 1162 m Concrete content 68 000 m3 Capacity of the spillway 2 322 m3/s Reservoir Gross Storage capacity 205 000 000 m3 Maximum depth ±32,5 m Mean Depth 9,6 m Catchment area 4 112 km2 Surface 2 062 ha Length shoreline 56 km Urban runoff / return flows 103 million m3 Firm Yield (1990) 158 million m3 Full Supply Capacity 195 million m3 Mean Annual Run-off 163 million m3 Mean Annual Rainfall 670 mm/year Mean Annual Evaporation 1 690 mm/year

Table 1.1: Dam characteristics 1.4 Functions of the dam 16

1.4 Functions of the dam

In the past, the main function was irrigation and supplying drinking water for the expan- ding communities of Johannesburg and Pretoria. However, as the eutrophication problem started in the mid- seventies, the large- scale production of drinking water stopped.

In Nowadays the dam has three main functions: recreation, irrigation and production of drinking water. Sometimes, the dam is also used for ﬂood control.

1.4.1 Irrigation

The most important function of the dam is irrigation (80% of the usage). Today irrigation canals are supplied with 110 - 150 million m3 of water per annum depending on weather conditions. This irrigation water flows through a 532 kilometres long network of canals to 159,76 km2 of farmland, lying northwest of the dam, on which tobacco, wheat, fruit and flowers are produced.Depending on the water quality, the water is drained from another depth of the dam reservoir. During severe eutrophication periods, the irrigation water schould be purified. Typically for southern Africa are the centre pivot irrigation systems which can easily be recognised from the air (figure 1.13).

1.4.2 Industry and mining

The irrigation canals and crocodile river also supply a lot of water for the mines (platinum and vanadium) and heavy industries around the town of Brits, downstream (north) of the dam.

1.4.3 Recreation

Another very important function of the dam is recreation. The dam and its immediate surroundings is a major tourist attraction and it offers magnificent opportunities for water activities, mountain sports and a variety of other activities such as hiking, angling, yachting, sailing, ballooning hang-gliding, parasailing and abseiling (figure 1.14). 1.4 Functions of the dam 17

Figure 1.12: Dam wall and outﬂow systems

Figure 1.13: Irrigation in the area of HBPD 1.5 References 18

Hartbeespoort has become a very popular holiday and weekend resort for the inhabitants of Johannesburg and Pretoria. Nowadays, it is the principal water recreation area of Northern Gauteng. For this reason, a suﬃcient water quality is indispensable.

Figure 1.14: Transvaal Yacht Club at Cosmos (Hartbeespoort)

1.4.4 Production of domestic drinking water

Madibeng Local Municipality depend totally on the irrigation water from HBDP. All inhabitants around the dam and large settlements downstream, including the town of Brits, use puriﬁed dam water for drinking. The existing drinking wtar treatment plants are outdated and have a very low capacity. In the near future, they won’t meet the going standards anymore.

1.5 References

Literature

A.R. Turton, R. Meissner, P.M. Mampane, O. Seremo. Hydropolitical History of South Africa’s International River Basins. Research Report No. 1220/1/04, 2004.

B. Harding. Hartbeespoort Dam: An Action Plan. Water Wheel Magazine, 2004 Volume 3 No 6 November/December, pages 6-10.

Blue-green algae - making water dangerous. WRC, Water Wheel Magazine, 2009 Volume 8 No 5 September/October, pages 36-37. 1.5 References 19

Brochure: Harties, Metsi A Me ”My Water” - Hartbeespoort Dam Integrated Biological Remediation Progamme. DWAF, Rand Water, November 2007. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

Fifty Years of Consulting Engineering in South Africa - The Construction of Hartbeespoort Dam. The South African Association of Consulting Engineers, Civil Engineering Magazine, June 2004, Vol 12 No 6.

F.J. Botha. Water Quality Monitoring: Presentation Principles, Approaches and Tech- niques - Case Study 9.1:Hartbeespoort Dam. 2008.

Madibeng Municipality. Draft Annual Report 2005/2006. Madibeng Municipality, pages 8-11, 2006.

National water resource strategy. South Africa’s water situation and strategies to balance supply and demand Crocodile (West) and Marico WMA. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

P.J. Ashton, F.M. Chutter, K.L. Cochrane, F.C. de Moor, J.R. Hely-Hutchinson, A.C. Jarvis, R.D. Robarts, W.E. Scott, J.A. Thornton, A.J. Twinch,

T. Zohary. The limnology of the Hartbeespoort Dam. Limnology Division of the National Institute for Water Research, CSIR, WRC and Foundation for Research Development. South African National Scientiﬁc Programmes Report no. 110, 1984.

P. Venter. Presentation Harties - Metsi A Me Remediation Program: An integrated biological remediation & management approach at the dam. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

P. Venter. Presentation: Eutrophication in the Hartbeespoort Dam Catchment - An integrated biological management approach at the dam. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

P. Venter. Presentation: Hartbeespoort Dam Integrated Biological Remediation Project. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

R.G. Noble, J. Hemens. Inland water ecosystems in South Africa-areview of research needs. Inland Water Ecosystems National Programme for Environmental Sciences. South African National Scientiﬁc Programmes Report no. 34, 1978. 1.5 References 20

River Health Programme. State-of-Rivers Report: Monitoring and Managing the Ecological State of Rivers in the Crocodile (West) Marico Water Management Area. Department of Environmental Aﬀairs and Tourism Pretoria, March 2005.

SA’s Water History - Taming the Poort. WRC, Water Wheel Magazine, 2008 Volume 7 No 3 May/June, pages 19-21.

T. Boshoﬀ. North West Environmental Management Series 5: Dam Remediation Hart- beespoort Dam. North West Provincial Government Maﬁkeng, South Africa, 2005.

W.R. Harding, J.A. Thornton, G. Steyn, J. Panuska, I.R. Morrison, Hartbeespoort Dam Remediation Project (Phase 1) - Volume I - Action Plan. NWP Dacet, DH Environmental Consulting, October 2004.

W.R. Harding, J.A. Thornton, G. Steyn, J. Panuska, I.R. Morrison, Hartbeespoort Dam Remediation Project (Phase 1) - Volume II - Action Plan. NWP Dacet, DH Environmental Consulting, October 2004.

Digital sources

Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Hartbeespoort Dam

HBPD Remediation Program oﬃcial website. http://www.dwaf.gov.za/Harties/

Kormorant - newspaper: The engineer who saved the dam. 30/07/2009. http://196.3.165.92/hartiesdev/media/Kormorant30Jul09.pdf

P.A. Nightingale. Damming the Poort. 1991. http://196.3.165.92/hartiesdev/documents/HartbeespoortDamConstruction1991.pdf

Hartbeespoort Government Water scheme. DWAF, 1991. http://196.3.165.92/hartiesdev/documents/HartbeespoortWaterScheme1991.pdf PROBLEM STATEMENT AND OBJECTIVE 21

Chapter 2

Problem Statement and Objective

2.1 Problem Statement

The poor water quality has adverse impacts on the usability of water, recreation possibilities and property values. Often swimming and water-skiing may end up in rashes or even more serious health problems. Domestic and wild animals die after consuming a suﬃcient quantity of toxic water. The greatest problem in containing the pollution of the dam is the many factors that cannot be controlled. In the following sections, this extensive problem will be discussed.

2.1.1 Waste

Heavy rains in the summer will bring flooding to the Witwatersrand area including the Crocodile, Hennops and Jukskei Rivers, which are the main sources of water flow into Hartbeespoort Dam. The unfortunate result is that a significant amount of water hyacinth and trash will wash into the Dam (figure 2.1).

When it rains heavily, the level of pollutants that enter the Dam can be five times higher than normal because of dry waste that is being washed into the water. These include matter such as fertilizer leached from cultivated lands, dry human and animal waste, water running through rubbish dumps and various other pollutants. A lot of waste is dumped by the inhabitants of the squatter camps along the river. Another problem is sewage water that enters unpurified in the river. Storm water that ends up in municipal sewage systems is a major cause of sewage entering the Dam during or after heavy rains. The problem is that antiquated sewage systems have been designed and constructed without regard 2.1 Problem Statement 22 to sewage systems and are inaccessible now. Also the uncontrolled extension of squatter camps, without any form of sewage purification provided, make the problem more worse.

Figure 2.1: Litter accumulation in the dam

2.1.2 Eutrophication

The combination of high nutrient loading, high incident solar radiation, low wind speeds and warm water makes it the ideal environment for the prolific growth of the buoyant blue- green algae. The water of Hartbeespoort Dam has been extremely eutrophicated for several decades due to excessive nutrient loading that originates largely from wastewater treatment discharges into the Jukskei River in Johannesburg. Nine wastewater treatment works (figure 2.2) discharge their 620 million litres per day of purified effluent into the Crocodile River and its tributaries. Very high loads of waste water effluents, with polluted stormwater from the catchment, intensify the occurrence of blue-green algae or cyanobacteria. 2.1 Problem Statement 23

Figure 2.2: Point discharges in the Upper Crocodile WMA

Because of this waste, the level of pollutants in the inflow is rising continuously. Over the last years, the regular inflow has risen by 50% while the inflow of phosphorus has increased by 100 %. The monitoring process has identified several impactors on the condition of the water, such as the Johannesburg’s Northern purification works. The notorious Tweelop- iespruit and Blauwbank, tributaries of the Jukskei River also carry mining pollutants to Hartbeespoort Dam, but some of the worst impactors are the squatter camps along the banks of the Jukskei. The Jukskei River carries 47 percent of all pollutants that end up in the Dam. Pollutants delivered directly into the dam basin are not as high as that delivered by the feeding rivers but because they are direct, there is no dilution effect such as when pollutants are carried over a distance. Although the percentage of waste, such as sewage spills and run-off, ending up directly into the dam may be relatively small, its impact is more direct as they are often close to points where water is being extracted for domestic purposes.

Every year over 170 tonnes of phosphorus is discharged into the dam. The combination of nutrient availability and suitable biophysical factors (such as temperature, water depth and water ﬂow) cause dense cyanobacteria growth in the water. The overwhelming algal blooms create a characteristic set of problems that have prevailed in the Hartbeespoort Dam ever since the early 1970’s. For many years the rehabilitation possibilities of the HBPD focused on the control of phosphate at point source discharges, which was seen as 2.1 Problem Statement 24 the only solution. Biological rehabilitation means were parked and forgotten about.

Hartbeespoort Dam is one of the most signiﬁcant dams in the economic hub of North West Province and of the Crocodile West Marico Water Management Area (WMA). The dam is one of the nine hypertrophic dams in South Africa. Seven of those nine are located in the Crocodile Marico catchment (ﬁgure 2.3). A hypertrophic state means there are excessive nutrients like phosphate and nitrogen in the dam. This is due to a combination of factors:

Figure 2.3: Seven of the nine hypertrophic dams in RSA are located in the Crocodile Marico catchment

• Waste Water Treatment Plants discharge more than 620 million litres per day (from Northern Sewage Works, via Jukskei) of treated eﬄuent into the catchment which put a load of more than 166 tons per annum of phosphate in to the Dam. The waste load enters the Dam with the incoming water from the Crocodile River which ﬂows into the Dam from Gauteng and brings with it waste from three Metropolitan areas, namely Johannesburg, Ekurhuleni and Pretoria.

• Infrastructure backlogs result in grey water washing to enter the rivers which ﬂow directly into the Dam, namely the Crocodile River, Magalies River, Leeuwspruit and the Swartspruit. 2.1 Problem Statement 25

• Storm water ingress into sewage networks that cause overﬂows from manholes and pump stations into water courses.

• Storm water ﬂows washing surface pollution such as sewage spillages, fertilizers, litter, animal waste etc. into the dam.

• Modiﬁed and destructed river banks, river beds and wetlands in the catchment have reduced the natural puriﬁcation capacity of the rivers.

The high concentration of nutrients (especially Phosphate) in the Dam results in uncontrolled growth of waterweeds (hyacinth) and algae (an algal bloom), especially during summer months when solar radiation and water temperature are high. This process is knows as eutrophication. Eutrophication also favours bottom dwelling fish, such as carp and catfish, that bring nutrients back into the water. These fish are contributors to the mass development of blue-green (cyanobacteria) and other algae. The destruction of natural habitat like the shoreline vegetation further contributes by distorting the food web and the entire aquatic ecosystem. This results in the dominance of three undesired fish species, namely Carp, Barbel and Canary Kurper, and the depletion of zooplankton and the desired fish species, the Mozambique Tilapia, which feeds on the algae.

Algal blooms and rotting hyacinths spoils the aesthetic appearance of the dam and negatively affects recreational activities such as water-sports and angling (figure 2.4). A further consequence is the unpleasant odours and these in turn may also influence the taste of domestic water. Depending on the maintenance and upkeep of the domestic water supply, the toxins could collect in the system and therefore be released into the domestic water.

Figure 2.4: Algae accumulation near the dam 2.1 Problem Statement 26

Water hyacinth has distinct plusses and minuses associated with its presence in the Dam. On the plus side, floating islands of water hyacinth, with its root system dangling free in the water, both absorbs phosphate which deprives the algae of a food source and provides a natural habitat where algae-eating zooplankton and indigenous fish can breed and grow. In addition, these floating islands provide a natural habitat for many of the bird species around the Dam. The big minus of water hyacinth is that it will aggressively establish itself and can spread rapidly, doubling its area of coverage in six weeks. It blossoms with a pleasant smelling purple flower. Water hyacinth is known as a ”pioneer” plant which means that it seeks to replicate itself, particularly near the shore where successive generations die off and drop to the bottom, eventually filling in the water and turning it into a marshy wetland. Water hyacinth is not indigenous so there is no natural mechanism to control its growth and spread.

Cyanobacteria

First of all, large cyanobacteria blooms may rapidly clog not only the fine sand filters but even the primary coarse fast filters of water treatment plants. They also reduce the carrying capacity of pipelines and canals. This means that the quality of the water is being affected as well as the cost to purify the water for household use.

Secondly, cyanobacteria may release substances in the water that are harmful or toxic, which cause unnatural colouration of the raw water or which add an objectionable odour or taste to drinking water. Toxic cyanobacteria found in eutrophic, municipal and residential water supplies are an increasing environmental hazard in South Africa. Cyanobacteria produce lethal toxins, and domestic and wild animal deaths are caused by drinking water contaminated by these toxins. Among the species causing death of livestock, blooms of Microcystis aeruginosa are the most common in South Africa. More than 65 microcystins have been isolated to date and they are the most abundant cyanobacterial toxins. Hazards to human health may result from chronic exposure via contaminated water supplies. Mi- crocystins are powerful tumour promoters and they are suspected to be involved in the promotion of primary liver cancer in humans. The algae toxin (microcystin) levels of the water in HBPD are regularly so high, that according to the international guidelines of World Health Organisation (see ﬁgure 4.7 in section 4) all uses of the water, including swimming and water-skiing, should be banned seasonally.

More information on the ecological problems can be found in section 4: Ecological Model. 2.1 Problem Statement 27

2.1.3 Erosion and sediments

Sedimentation oﬀers a two-fold problem: it reduces the capacity of a dam and it traps pollution so that it does not wash out naturally with the ﬂow of the water. 15% of the content is regarded as the threshold for sedimentation in a dam, but in the case of Hartbeespoort Dam the sediment content has already reached the 20% mark. The reduce in capacity is not the major problem, the content of the sediment is.

Historic and present pollution loads are trapped in the sediments, which constantly release additional nutrient loads (Carbon, Nitrogen, Phosphorous) into the water of the Dam. Over a period of more than 87 years (since 1923) between 30 and 40 million cubic metres of sediment has been deposited in the dam, trapping tons of nutrients in the form of carbon, nitrogen and phosphorous resulting in ecosystem degradation and the release of toxins. The build-up of the nutrients is the result of effluent from municipal and industrial sources, raw waste water, sewage spills, urban storm water and arable land run-off, amongst others. Near the dam wall where the dam is about 42 metres deep, about 14 to 18 metres is sediment (figure 2.6). In the deep zone of the Main Basin, the sediment layer is about 12-14 m underneath FSL with column height ranges from 5 - 7 m. The total estimated volume of sediments in this zone ranges from 22 - 25 x 106 m3. An overview of the sedimentation zones id given in fugure 2.5.

Figure 2.5: Sediment zones in the impoundment 2.1 Problem Statement 28

The initial deposit of sediment takes place where the river mouths into the open water and the ﬂow velocity is reduced. Over the years the slope of the ground carries the sediment towards the dam wall where it forms various layers, the deepest of which is anaerobic or deprived of oxygen and does not carry nutrients. The upper layer consists of a jelly like substance and this is where most of the nutrients are trapped. This jelly layer originated in the mid seventies, when all of the hyacinths and algae were killed by herbicides. All the dead plants sunk to the bottom and formed a gelatinous layer, which is today still present (about 1.5 million m3).

Figure 2.6: Sediment cross- section near the dam wall

Turbidity caused by ship propellers and the carp and catﬁsh causing bio-turbation, resuspension of nutrients back into the water is making these available for algal growth again. In general, the dam would be better oﬀ if this major source of nutrients is removed.

Main sources of the sediments, supplied by the feeding rivers, are sand mines near the Jukskei River and destroyed wetlands and riparian zones.

2.1.4 Groundwater

In the Crocodile (West) Marico Catchment, there exist large dolomitic aquifers along most of the southern part of the WMA from Pretoria to Maﬁkeng. Its quality is generally of a 2.1 Problem Statement 29 very high standard, so large quantities of water are abstracted from these aquifers, mainly for urban and irrigation use. In the vicinity of Maﬁkeng however, an overexploitation of groundwater is experienced.

2.1.5 Agriculture

The algae produce toxins, which make the water, non-potable for animals (wild animals and livestock). Also, during periods of serious eutrophication, extra treatment of the irrigationwater is needed. This results in extra costs for the farmers and extra health risks for the consumers of these products.

2.1.6 Domestic consumption

Because of the algal toxins, the water is definitely non- potable for human beings. It results in high purification costs and bad taste after purification.

2.1.7 Developments

For inhabitants, tourism and lodging operators, the problems can result in a reduced influx of tourists, loss of businesses and job opportunities. The dam lacks the attraction of a clean and safe water body. Seasonally strong unpleasant odours, excessive algal growth. Then, the dam is not pleasant for recreation. The anglers and recreational users will get annoyed at the algal mats and scums, the reduced diversity of fishery, the bad taste and odours in fish flesh, the reduced visibility of water, . . . Proprietors will have to deal with reduced property values.

2.1.8 Conclusions

All this results in the fact that Hartbeespoort Dam is (one of) the most severely stressed dams in the country. One of the stress factors are the inattentive developments and ex- pansions around the dam and in the catchment area, resulting in severe eﬀects on the ecosystems. There is no single factor, such as nitrogen content, that is responsible for the state of the water. A dam such as Klipvoor Dam, for instance has about four times the phosphorous content of Hartbeespoort Dam, but because of the adequate shoreline vegetation it maintains a better balance. 2.2 Objective of the master thesis 30

2.2 Objective of the master thesis

One of the deﬁnitions of Ecohydraulics could be: ecohydraulics covers the integration of the instream and riparian ecology with the physical determinants of the habitat such as ﬂow, water level, sediments, etc. There is increasing international recognition of the importance of ecohydraulics as it strives to describe the complexity of the real river. The better understanding and untangling of the complexities of aquatic systems require an interdisciplinary approach. Although the hydraulic and hydrological models have become more and more precise and sophisticated. They are often not appropriate to use because of the lack of data to build and calibrate them.

The Strive (STream RIVer Ecosystem) model, a numerical model allows integrated modelling. Aim is to study hydraulic as well as ecological variables in the dam and river and their interaction. The core hydraulic module is based on the Saint-Venant equations (more information in paragraph 3.2.1).

Purpose of the model is to simulate various scenarios over a longer period with the aim to work out how the eutroﬁcation problem in the dam can be solved in the best way. It should help to predict the future developments, trace the critical points and assign priorities. It should beneﬁt for the current research projects and an aid for developing future plans.

2.2.1 Hydraulic model

In the first part, purpose is to make a hydraulic model of the Hartbeespoort Dam and its main supplying river, the Crocodile River. This river will be modelled in one dimension, starting from the most upper river flow station, until the discharge in the Hartbeespoort dam. The flow of its three major tributaries will be taken into account. In the future (the continuation thesis), dam reservoir will be put into a two dimensional model. The reservoir will be fed by the Crocodile River and two other tributaries; the outflow is simulated by two irrigation channels and the continuation of the Crocodile River.

2.2.2 Ecological model

In the second part of the modelling, an ecological model is made. An algae growing model and pollution spreading model will be the main subjects. Also the inﬂuence of wetlands 2.3 References 31 will be discussed. In the end, the purpose is to make a correlation between the hydraulic model ecological model.

Many ecological eﬀects can arise from stimulating primary production, but there are three particularly troubling ecological impacts: decreased biodiversity, changes in species composition and dominance, and toxicity eﬀects. In the ecological model, the following aspects should be treated:

• Increased biomass of phytoplankton

• Toxic or inedible phytoplankton species

• Increases in blooms of gelatinous zooplankton

• Decreased biomass of benthic and epiphytic algae

• Changes in macrophyte species composition and biomass

• Decreases in water transparency (increased turbidity)

• Colour, smell, and water treatment problems

• Dissolved oxygen depletion

• Increased incidences of ﬁsh kills

• Loss of desirable ﬁsh species

• Reductions in harvestable ﬁsh and shellﬁsh

• Decreases in perceived aesthetic value of the water body

• Decreased biodiversity

2.3 References

Literature

B. Harding. Hartbeespoort Dam: An Action Plan. Water Wheel Magazine, 2004 Volume 3 No 6 November/December, pages 6-10. 2.3 References 32

Blue-green algae - making water dangerous. WRC, Water Wheel Magazine, 2009 Volume 8 No 5 September/October, pages 36-37.

Harties, Metsi A Me ’My Water’ - Hartbeespoort Dam Integrated Biological Remediation Progamme. DWAF, Rand Water, November 2007. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

J. Kruger. Presentation: Hartbeespoort Dam Remediation Programme - Biological Reme- diation - Local ﬁnancing solutions. ICA Conference, Dakar 26-27 November 2008.

O. Sawadogo, G. Basson. Analysis of Observed Reservoir Sedimentation Rates in South Africa. African Institute for Mathematical Sciences (AIMS), University of Stellenbosch, South Africa, May 2008.

P.J. Ashton, F.M. Chutter, K.L. Cochrane, F.C. de Moor, J.R. Hely-Hutchinson, A.C. Jarvis, R.D. Robarts, W.E. Scott, J.A. Thornton, A.J. Twinch, T. Zohary. The limnology of the Hartbeespoort Dam. Limnology Division of the National Institute for Water Re- search, CSIR, WRC and Foundation for Research Development. South African National Scientiﬁc Programmes Report no. 110, 1984.

P. Venter. Presentation Harties - Metsi A Me Remediation Programme: An integrated biological remediation & management approach at the dam. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

South African National Water Quality Monitoring Programmes Series. National Eutro- phication Monitoring Programme - Implementation Manual. Department of Water Aﬀairs and Forestry, First Edition, 2002. 2.3 References 33

T. Boshoﬀ. North West Environmental Management Series 5: Dam Remediation Hart- beespoort Dam. North West Provincial Government Maﬁkeng, South Africa, 2005.

Z. Cukic. Presentation Hatrtbeespoort Dam: Internal Load Issues. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

Z. Cukic, W. Potgieter, P. Venter. Metsi A Me Project - Hartbeespoort Dam Restoration and Rehabilitation - Task B5: Sediments Removal and Management. Metago Engineering Services - Johannesburg, Enhanced Engineering Solution - Pretoria, March 2009.

Digital sources

Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Eutrophication

Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Hartbeespoort Dam

Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Algal blooms

Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Cyanobacteria

Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Cyanotoxin

HBPD Remediation Program oﬃcial website. http://www.dwaf.gov.za/Harties/ HYDRAULIC MODELLING 34

Chapter 3

Hydraulic modelling

In this chapter, the complete modelling proces will be worked out. First, an overview of thedataisgiven.

3.1 Collected data

During the ﬁeld visit, all the necessary data was collected at the diﬀerent agencies. An overview is given below.

3.1.1 Flow Data

The upper Crocodile River and Hartbeespoort Dam contain a number of flow gauging stations. In these stations, there was at least flow data available for the last 20 years. Also the tributaries Swartspruit, Magalies River, Hennops River, Jukskei River and Bloubank Spruit have a gauging station, providing at least 20 years of data. A scheme of the rivers and their gauging stations is mentioned in figure 3.2. The discharge of the HBPD consists of two irrigation canals and the continuation of the Crocodile river towards the confluence with the Limpopo River.

The flow data is obtained from water level measurements at the different weirs. At those river gauging stations, at the side of the river, level registration equipment is installed. The measured level is transformed to a flow by help of a level- flow- curve (see figure 3.1.The STRIVE- software is able to use the equitation of the curve to make a correlation between the level and flow. This correlation stipulates the downstream boundary conditions for 3.1 Collected data 35 several sections of the Crocodile River. There is hourly, daily and monthly data available for each weir (provided by DWAF). Particulary hourly data is used.

Q z relation for weir A2H050

200

180

160

140

120

(m³) 100 w Flo 80

0 0 050,5 1 151,5 2 252,5 3 353,5 Waterlevel(m) Q=14.099Z2.294 Data Trendline

Figure 3.1: Flow - level - correlation for weir A2H050

3.1.2 Evaporation Data

Evaporation losses are one of the many components that should be evaluated in the model, particularly because the net evaporation is signiﬁcant relative to the water resources. A preliminary estimate of losses from a river can usually be obtained by multiplying the water surface area by an appropriate evaporation rate, for example from evaporation pan data.

The evaporation data is available on daily base for the town of ’De Rust’, near the HBPD. The quantity of evaporated water depends on several factors such as surface, temperature and sunlight intensity. In the upper crocodile, the share of water losses due to evaporation will be limited, but in the dam reservoir, it will have a large inﬂuence. For HBPD, the evaporation is concentrated during the summer months (October till March) (see ﬁgures 3.3 and 3.4). 3.1 Collected data 36

Westirrigation damoutflow canal A2H083 A2H081 Eastirrigation canal Crocodile River A2H082

MagaliesRiver Hartbeespoort A2H013 Dam reservoir Swartspruit

A2H058

8,197km Moganwe (no dataavailable) A2H012

6,89km 13,39km Hennops River

A2H014 5,8km 3,15km Jukskei River 2,94km A2H044 A2H045 ver

18,9km

Bloubank Spruit Crocodile Ri

A2H049 2,17km

A2H050

5,87km

A2H051

=Riverflow stationswith atleast 20years ofdata

Figure 3.2: Overview of the hydraulic scheme of the Crocodile River and HBPD 3.1 Collected data 37

Figure 3.3: Average monthly evaporation

Figure 3.4: Daily evaporation

3.1.3 Rainfall data

Climatic conditions in the Crocodile (West) Marico WMA vary signiﬁcantly from east to west. The climate across the Water Management Area is temperate, and semi-arid in the east to dry in the west. Rainfall is strongly seasonal, with most rainfall occurring as thunderstorms during the summer period of October to April. Mean annual rainfall in 3.1 Collected data 38

HBPD ranges from 60 to 200 mm and decreases from the eastern to the western side of the WMA (see ﬁgures 3.5 and 3.6).

The DWAF provides rainfall data from the meteorological station in ’De Rust’, a town near the dam. It is provided on daily and monthly base.

Figure 3.5: Average monthly rainfall

Figure 3.6: Daily rainfall 3.1 Collected data 39

3.1.4 Cross sections

For all the used weirs, extensive constructive data (blueprints) is available. Also data on cross sections of the rivers, a couple of metres before and after the weirs, is available. Unfortunately, of the Crocodile river (and tributaries) itself, there are no cross sections, nor detailed longitudinal sections available. The available cross sections are imported in the STRIVE- software, and these derives cross sections for every box. On the blueprints, the exact position and altitude of the bottom of the river bed and weir is mentioned.

The data about cross sections is available on the CD, in the folder ”Cross sections” (see also annex D).

Figure 3.7: Longitudinal section of the total Crocodile River

3.1.5 Longitudinal sections

As there was no exact data available on the longitudinal sections of the rivers, by help of the GPS- coordinates of the weirs and ’Google Earth’, the length of each river section could be determined. Also, digital elevation maps of the region were provided by DWAF (GIS- Department). These DEM gave extra information on the slopes of the river, especially where the rapids and weirs occurred. In literature (J. Moolman, 2002), information on the total longitudinal section of the CR was obtained (see ﬁgure 3.7). The altitude of the 3.2 Model 40 sections of the river that will be modelled, extend from 1155 to 1400 m a.s.l.)

3.2 Model

3.2.1 Background information

Femme - STRIVE

The environment ’Femme’ (’a flexible environment for mathematically modelling the environment’) is used to model ecological processes as the transport of nutrients and polluents. The program is user-friendly and based on a Fortran modular open source code and uses a lot of integrated integration tools. For the study of the interaction of ecological processes and flow in the river, a realistic modelling of the surface water flow is necessary. Here, the implementation of a one dimensional hydrodynamic model for surface water flow in Femme is reported. First of all, the kinematic and parabolic equations were implemented. After some calculations, it seemed necessary to use the complete Saint- Venant equations to solve the problems of instability.

’Femme’ or ’a flexible environment for mathematically modelling the environment’ is developed by NIOO (Nederlands Instituut voor Ecologie, Netherlands Institute of Ecology). Femme is a modelling environment for the development and application of ecological time dependent processes by use of numerical integration in the time of differential equations. The program is written in Fortran and exists of an open source code and a modular hi- erarchical structure. Femme consists of a wide range of numerical calculations and model manipulations (as integration functions, forcing functions, linking to observed data, cal- ibration possibilities, etc.). These technical possibilities allow the user to focus on the scientific part of the model and detailed research of the model without the confrontation with real program linked problems. Femme is focused on ecosystem modelling, is open source (no black box) and a modular system (implementation of different models next to each other). The Strive package has been developed using the Femme environment. A 1D hydrodynamic model for unsteady free surface flow based on the Saint-Venant equations has been implemented, yielding accurate modelling of surface flow characteristics, which subsequently has been coupled to ecological processes to achieve the required interaction between the subsystems of the ecosystem.

In a ﬁrst stage, a water transport model is developed in STRIVE. This model uses the 3.2 Model 41

Saint- Venant equations to describe the surface water flow in rivers. In a multidisciplinair approach of ecosystem studies, also sediment transport, macrophyte growth and suspended solids have to be incorporated. Therefore, using a modular approach in the Femme environment allows to study the interaction of macrophytes, water transport, sediments and suspended solids. Furthermore, different stream models and varying biomass can easily be incorporated. Figure 3.8 shows a flowchart of the Strive package.

Figure 3.8: Flow chart of Strive (after K. Buis)

Figure 3.9 shows conceptual model of a South African river. In the hydraulic model, the amount of groundwater inflow and the bank seepages will be assumed as equal, so they can be ignored. On most of the tributaries, data is available (see figure 3.2). Sand banks especially occur at the mouth of the CR in the HBPD. They have influence on the path 3.2 Model 42 of the river, and will be implemented in the model (as far as the cross sections of this part of the river are available). On the upper Crocodile River, no municipal and industrial abstractions are done, but they occur in the lower parts of the river. On the irrigation abstractions, no exact data is available, so no notice is took on these flows.

Figure 3.9: Conceptual model of a South African River (source: WRC) 3.2 Model 43

Saint-Venant equations

In this subsection, the equations of 1D unsteady open channel ﬂow are studied in more detail. These equations will make up the core of a hydraulic model.

River flow has not at all a permanent nature due to rainfall. Surface water flow is mathematically seen as the propagation of a wave in a river. Registration of the hydrograph (i.e. the discharge as a function of time) in two different sections of the river shows a shift of the peak and flattening of the peak due to storage and dissipation of the energy by bottom fiction. Flood routing or the calculation of the propagation of waves in a river bed can give information about maximal discharge (design of bridges, cannel sections), maximum water level (flooding), determination of the flooded area, etc.) In applications, the river channel is divided into a number of computational reaches and the shallow water wave equations (so called Saint-Venant equations) are applied to each reach. By using an implicit finite difference scheme, called the Preissmann scheme, and the Double Sweep algorithm, the equations for all reaches are solved simultaneously.

Surface water flow is mathematically seen as the propagation of a wave in a river. Regis- tration of the hydrograph (i.e. the discharge as a function of time) in two different sections of the river shows a time shift of the peak and flattening of the peak due to storage and dissipation of the energy by bottom friction. Time shift and flattening of the peak of the wave are observed by studying waves at two different places in rivers (Figure 3.10). Flood routing or the calculation of the propagation of waves in a river bed can give information about maximal discharge (design of bridges, channel sections), maximum water level (flooding), determination of the flooded area, etc.

Figure 3.10: Hydrograph in two sections (I and II) of the river, with indication of time shift and peak ﬂattening 3.2 Model 44

One dimensional non-permanent surface water ﬂow is expressed by the Saint-Venant equations. These consist of the continuity equation and the momentum equation.

The continuity equation is the description of the storage of the water in the diﬀerent cells: ’the net rate of ﬂow into the volume is equal to the rate of change of storage inside the volume’.

In Q(x,t) and z(x,t)

∂Q B∂z + = q ∂x ∂t (3.1)

(a) = convective ﬂow (b) = storage (c) = lateral inﬂow

In Q(x,t) and h(x,t)

∂Q B∂h + = q (c) ∂x (a) ∂t (b) (3.2)

The momentum equation describes the transport of the water between the neighbouring cells: ’the net rate of momentum entering the volume plus the sum of all external forces 3.2 Model 45

(pressure, gravity, friction) acting on the volume is equal to the rate of accumulation of momentum’.

In Q(x,t) and z(x,t)

∂Q ∂ Q2 ∂z Q + ( )+gA(Sf + )=q ∂t ∂x A ∂x A (3.3)

In Q(x,t) and h(x,t)

∂Q ∂ Q2 ∂h Q + ( ) (b) − gA(S0(c) − Sf (d) − )=q ∂t (a) ∂x A ∂x (e) A (f) (3.4)

(a) local acceleration term: change in momentum, due to change in velocity over time (b) convective acceleration term: change in momentum, due to change in velocity along the channel (c) pressure force term: proportional to change in water depth along the channel

(d) gravity force term: proportional to the bed slope S0

(e) friction force term: proportional to the friction slope Sf (f) lateral inﬂow

(d) kinematic wave: assumes S0 =Sf (c) + (d) diﬀusion wave: incorporates pressure term

The Saint-Venant equations are based upon the following series of assumptions: 3.2 Model 46

• The ﬂow is one-dimensional i.e. the velocity is uniform over the cross section and the water level across the section is horizontal;

• The streamline curvature is small and vertical accelerations are negligible hence the pressure is hydrostatic;

• The eﬀects of boundary friction and turbulence can be accounted for through resis- tance laws analogous to those used for steady state ﬂow;

• The average channel bed slope is small so that the cosine of the angle it makes with the horizontal may be replaced by unity.

Manning’s Roughness coeﬃcient

An important parameter in the Saint-Venant equations is Mannings roughness coefficient calculated from the energy slope. Different methods and procedures are described in literature to come to the value of Mannings coefficient. As all the different approaches in determining the roughness coefficient show great variability of n, they do not guarantee accurate values. All existing methods are based on particular research in selected rivers or flumes. These values are only indicative and not simply transferable to other measurement set ups or rivers. Therefore, it is recommended to determine the roughness starting from measurements on the Crocodile River. For steady state conditions and assuming uniform flow, the roughness coefficient in the Saint-Venant equations is described using the Man- ning equation. An exact known Manning coefficient would largely increase the accuracy of the model.

3.2.2 Crocodile River

The process of computing the progressive time and shape of a flood wave at successive points along a river, is called flood routing (also known as storage routing or streamflow routing). This principle will be used in an adapted manner. To calibrate each section, flood data is extracted from the flow data, and the manning coefficient (unknown parameter) is adapted until the modelled flood equals the measured flood. A longitudinal section based on the availlable data is represented in figure 3.11. 3.2 Model 47

Figure 3.11: Longitudinal section of the CR, based on the availlable data

Section A

The ﬁrst section of the Crocodile River that is modelled, streams from River Flow Station A2H051 (Van Wyks Restant) to A2H050 (Zwartkop) (ﬁgure 3.12 and 3.13). This section is characterized by the following data:

Section A From A2H051 To A2H050 Length 5870 m Bottom level upstream 1396,1 m Bottom level downstream 1354,6 m Tributaries none Level diﬀerence 41,5 m Mean slope 0,0071 m/m

Table 3.1: Characteristics of Section A 3.2 Model 48

Figure 3.12: River section A (source: Google Earth)

The following cross sections are used:

Cross- section Distance Width Bottom Left Bank Right Bank Bottom Level m m rad (°) rad (°) m a.s.l. 1 0 13,44 1,3926 79,7888 1,5674 89,8060 1396,81 2 50 10,69 1,4153 81,0925 1,3967 80,0227 1396,53 3 5794,3 15,04 1,4681 84,1156 1,3490 77,2936 1355,53 4 5870 22,47 1,4217 81,4568 1,3355 76,5165 1355,97

Table 3.2: Cross sections section A

The angle of the bank slopes in table 3.2 is indicated from the upright direction. Remark that cross- sections of the riverbed were only available near the weirs. As upstream boundary condition, an assumed water level is used. As downstream boundary condition, a level- discharge - correlation of the A2H050- weir is used (provided by DWAF). This correlation is plotted down in ﬁgure 3.1. To calibrate the model, a series of measured ﬂow data of station A2H051 is used.

The most important difficulty to model this section was the amount of water to store. Because of the high slope and large cross sections for low discharges, it was difficult to obtain realistic water levels. As in reality, some waterfalls, small weirs and dams are present on this section, but no data is available on those. Only with lower slopes, this part of the river could be modelled. On the rain data from the station in the rust (see data on the included CD), it is clear that every time there is a rain shower, a flood occurs in the river. 3.2 Model 49

To create a model that worked, a lot of simplifications and assumptions had to be done. The model didn’t want to work with the original slope, which is too high to obtain subcritical flow. The level was reduced by 50%, an assumption based on the fact that more than half of the drop is due to waterfalls and rapids, which can’t be modeled because of supercritical flow. DEM helped to develop this assumption. The best results that could be obtaineded, are represented in figure 3.14 and 3.15.

The manning used for this model is 0.16 for peak nine and 0.2 for peak six, which are realistic values. Small diﬀerences in manning values can be attributed to the excessive hyacinth growth in the river during speciﬁc periods. The models and results are included on the CD, in the folder Strive-model.

More research and data will be needed to make the model more accurate. Future modelling work should focus on the waterfalls, small dams and weirs in the river. Because there is no detailed information available on the bottom width and level, and the water levels in these areas a lot of uncertainties still exist. If more data is available on this, section A could be split up in several subsections, in which normal ﬂow occurs. In fact, waterfalls and rapids convert a lot of potential energy into turbulences, without contributing to the kinetic energy of the water (speed of the water).

Figure 3.13: The Crocodile River in section A 3.2 Model 50

Peak6 12/01/2006 25

15 rge(m³/s) a

10 Disch

0 1 1 2 2 3 3 4 4 5 0 5 0 5 0 5 0 5

A2H051 A2H050data A2H050model Time(hour)

Figure 3.14: Flood peak 6, with n= 0.2

Peak 9 19/10/2007

6 rge(m³/s) a

Disch 4

0 15 20 25 30 35 40 A2H051 A2H050data A2H050model Time(hour)

Figure 3.15: Flood peak 9, with n= 0.16 3.2 Model 51

Section B

The second section of the Crocodile River that is modelled, streams from River Flow Station A2H050 (Zwartkop) to A2H045 (Vlakfontein) (ﬁgure 3.16. After 2.17 km, a tributary called ’Bloubank Spruit’ mouths in the Crocodile River. Data from River Flow Station A2H049 is used to take the discharges from the Bloubank Spruit into account. This section is characterized by the following data:

Section B From A2H050 To A2H045 Length 21070 m Bottom level upstream 1354,23 m Bottom leveldown stream 1245,80 m Tributaries Bloubank Level diﬀerence 108,43 m Mean slope 0,0051 m/m

Table 3.3: Characteristics of Section B

The following cross sections are used:

Cross- section Distance Width Bottom Left Bank Right Bank Bottom Level m m rad (°) rad (°) m a.s.l. 1 0,0 9,81 1,340 76,789 1,380 79,057 1354,23 2 79,7 6,56 1,344 76,981 1,281 73,369 1353,31 3 158,6 10,91 1,298 74,364 1,252 71,752 1353,41 4 231,3 4,19 1,099 62,977 1,241 71,100 1352,37 5 321,0 6,89 1,323 75,787 1,394 79,866 1353,38 6 385,8 1,78 1,423 81,515 1,422 81,482 1352,97 7 454,6 22,80 1,457 83,472 1,479 84,727 1354,29 8 20970,0 8,84 1,442 82,617 1,490 85,397 1246,66 9 21065,2 3,34 1,448 82,943 1,453 83,268 1245,46 10 21070,0 29,61 1,442 82,642 1,288 73,812 1245,80

Table 3.4: Cross sections Section B 3.2 Model 52

Note that the gauging station A2H045 on the Bloubank Spruit is situated near the confluence with the CR (see figure 3.16). No flood routing on the discharge data is needed. The angle of the bank slopes in table 3.4 is indicated from the upright direction. Remark that cross- sections of the riverbed were only available near the weirs. As upstream boundary condition, an assumed water level is used. As downstream boundary condition, a level- discharge - correlation of the A2H045- weir is used (provided by DWAF). This correlation is plotted down in figure 3.17. To calibrate the model, a series of measured flow data of station A2H050 is used.

Figure 3.16: River section B (source: Google Earth)

Figure 3.17: Flow - level - correlation for weir A2H045

For section B, the same problems occured as in section A. The best result that could be obtained is represented in figure 3.18. A manning value of 0.18 was applied. This seems a 3.2 Model 53 realistic value, due to the large amount of rocks and plants in the river. However, because of the high average slope, a large manning could be necessary to obtain enough storage of water in the river. In this section, again a lot of rapids and small waterfalls occur. Even a large, private property dam just past the confluence with the Jukskei is present (see figure 3.16). More detailed information on those is needed, so a more accurate model, with a lower slope can be worked out. Again, the combination of very low average discharges, with quite large cross sections makes it very hard to model this section.

Peak1121/03/2006 25

15 rge(m³/s) a

10 Disch

0 50 55 60 65 70 75 80 85 90 95 100

Time(hour) A2H050 A2H045data A2H045model A2H049(Bloubank)

Figure 3.18: Flood peak 11, with n= 0.18

Section C

The third section of the Crocodile River that is modelled, streams from River Flow Station A2H045 (Vlakfontein) to A2H012 (Kalkheuwel) (figure 3.19). After 2.94 km, a tributary called ”Jukskei” mouths in the Crocodile River. Data from River Flow Station A2H044 is used to take the discharges from the Jukskei into account. This weir is close to the mouth, so on the Jukskei, no flood routing has to be done. The mean annual discharge of the Jukskei as about 173.9 million m3, the CR on this point in the river 38.89 million m3.As the Jukskei confluences, the Crocodile River becomes a much larger river. 5.8 km further on, a tributary called ”Hennops” contributes with the CR. This tributary is smaller, but with a mean annual discharge of 102.4 million m3, it is still much larger than the CR at 3.2 Model 54

A2H045. Both tributaries transport a lot of eﬄuents of the sewage treatment plants of the urbanized areas around Pretoria and Johannesburg. It results in a more continuous discharge than the ﬂow in the CR. This last one almost totally depends on precipitation. The section is characterized by the following data:

Section C From A2H045 To A2H012 Length 15630 m Bottom level upstream 1246,14 m Bottom leveldown stream 1171,41 m Tributaries Jukskei Hennops Level diﬀerence 74,735 m Mean slope 0,0048 m/m

Table 3.5: Characteristics of Section C

The following cross sections are used:

Cross- section Distance Width Bottom Left Bank Right Bank Bottom Level m m rad (°) rad (°) m a.s.l. 1 0,00 47,97 1,4136 80,9932 1,2453 71,3481 1246,14 2 12,00 34,14 1,4425 82,6491 1,4199 81,3561 1245,92 3 201,95 7,95 1,3599 77,9159 1,4739 84,4481 1239,04 4 421,86 13,67 1,4314 82,0128 1,1450 65,6028 1235,96 5 638,32 35,79 1,4537 83,2916 1,1543 66,1369 1236,60 6 854,28 40,27 1,4202 81,3741 1,4198 81,3510 1235,14 7 981,10 4,21 1,3127 75,2115 1,2648 72,4700 1230,22 8 1184,74 44,14 0,8944 51,2468 1,4285 81,8473 1231,81 9 15583,50 14,20 1,3723 78,6272 1,3578 77,7972 1170,84 10 15618,29 35,66 1,2378 70,9184 1,2813 73,4115 1171,43 11 15630,00 36,80 1,6156 92,5695 1,2342 70,7131 1171,41

Table 3.6: Cross sections Section C 3.2 Model 55

Figure 3.19: River section C (source: Google Earth)

The angle of the bank slopes is indicated from the upright direction. Remark that cross- sections of the riverbed were only available near the weirs. As upstream boundary condition, an assumed water level is used. As downstream boundary condition, a level- discharge - correlation of the A2H045- weir is used (provided by DWAF). This correlation is plotted down in ﬁgure 3.20. To calibrate the model, a series of measured ﬂow data of station A2H045 is used. 3.2 Model 56

Figure 3.20: Flow - level - correlation for weir A2H012

The weir of the Hennops River (A2H014) is located 13.39 km upstream the conﬂuence with the CR. However not much data is available, a ﬂood routing on this river is necessary. The upstream condition is the hydrograph of RFS A2H014, the downstream condition is the water level in the CR. Cross sections were only available near A2H045. The bottom level downstream of 1200 m a.s.l. was determined on the DEM of that area.

Section D

The fourth and final section of the upper Crocodile River that is modelled, streams from river flow station A2H012 (Kalkheuwel) to the outflow in the HBPD (figure 3.22 and 3.21). After 6.2 km, a tributary called ’Moganwe’ mouths in the Crocodile River. As this is a seasonal river and no data is available on the river, it is ignored in the hydraulic model. Section D is characterized by the following data: 3.2 Model 57

Section D From A2H012 To HBPD Length 8197 m Bottom level upstream 1169,87 m Bottom level downstream 1155 m Tributaries none Level diﬀerence 14,87 m Mean slope 0,0018 m/m

Table 3.7: Characteristics of Section D

The cross sections have the following characteristics:

Cross- section Distance Width Bottom Left Bank Right Bank Bottom Level m m rad (°) rad (°) m a.s.l. 1 0 15,40 1,1908 68,2298 1,4542 83,3203 1170,12 2 32,27 37,97 1,2230 70,0726 1,4221 81,4777 1170,40 3 48,17 35,16 1,2393 71,0085 1,3964 80,0104 1170,00 4 5648 565,00 1,3966 80,0212 1,5650 89,6683 1160,75 5 6241 124,50 1,1449 65,5992 1,2025 68,8965 1159,05 6 7044 140,00 1,0911 62,5134 1,4510 83,1363 1158,75 7 7692 305,00 1,4570 83,4802 1,5135 86,7191 1156,00 8 8197 340,00 1,5100 86,5167 1,5381 88,1255 1155,00

Table 3.8: Cross sections section D

The angle of the bank slopes in table 3.8 is indicated from the upright direction. Remark that cross- sections of the riverbed were only available near the weirs. The cross sections around the weir A2H012 were provided by DWAF, the cross sections near the dam were copied from a survey report, which is available on the included CD.

Figure 3.22 shows the path of the river in section D. The upstream boundary condition for this section is an assumed water level. The downstream boundary condition is the dam water level (data provided by DWAF). To calibrate the model, a series of measured ﬂow data of station A2H012 is used. 3.2 Model 58

Figure 3.21: A2H012: weir on the Crocodile River at kalkheuwel

Figure 3.22: River section D (source: Google Earth) 3.2 Model 59

Figure 3.23: Drop of river section D, based on the available data

The results of the model of section D are represented in figure 3.24. As there is no gauging station at the end of this section, there is no way to control if the assumed manning coefficient is reasonable, as done in the upper sections. The manning coefficient varies between 0.083 and 0.087. For other values, the model didn’t work. This is probably due to the large variation in the bottom with over small intervals.

For further optimization, more data is needed on water levels and the rapids and dammings just past weir A2H012. 3.2 Model 60

200

150 s) /

100 Discharge(m³

0 50 55 60 65 70 75 80 85 90 95 Time(h)

Distance0m Distance8197m n=0.087 Distance8197m n=0.083

Figure 3.24: Flood wave on section D

Figure 3.25: View on the CR, just before the mouth in the HBPD

3.2.3 Hartbeespoort Dam reservoir

In rivers, water movements could be reduced to one single dimension (current version of STRIVE). In impoundments however, water movements are often in two dimensions. The 3.3 References 61 modelling of the HBPD could not yet be developed, as the STRIVE- software is not ready yet for 2D modelling.

For the dam, a zero dimension model (point model) already exists, to control the level of the reservoir. In annex E, a part of this model is represented. The complete model is included on the CD.

3.3 References

Literature

C.W. Tsai. Applicability of kinematic, noninertia, and quasi-steady dynamic wave models to unsteady ﬂow routing. Journal of Hydraulic Engineering, volume 129, 2003.

E. van Dijk. Development of a GIS-based hydraulic-ecological model to describe the interaction between ﬂoodplain vegetation and riverine hydraulics. Master Thesis University of Twente, Enschede, January 2006.

H.H. Barnes. Roughness Characteristics of Natural Channels. U.S. Geological Survey Water-Supply Paper, 1987.

J.A. Cunge, F.M. Holly, and A. Verwey. Practical aspects of computational river hydraulics. Pitman Advanced Publishing Program, 1980.

J. Moolman, C.J. Kleynhans, C. Thirion. Channel slopes in the Olifants, Crocodile and Sabie River catchments. Department of Water Aﬀairs and Forestry Institute for Water Quality Studies, October 2002.

K. Soetaert, V. deClippele, P. Herman. FEMME, a ﬂexible environment for mathematically modelling the environment, Ecological Modelling. Volume 151, Pages 177-193, 2002.

K. Buis, C. Anibas, R. Banasiak, L. De Doncker, N. Desmet, M. Gerard, S. Van Belleghem, Batelaan O., P. Troch, R. Verhoeven, and P. Meire. A multidisciplinary study on exchange processes in river ecosystems. In W3M, Wetlands: Monitoring, Modelling, Management, Wierzba, Poland, 2005.

L. De Doncker. A Fundamental Study on Exchange Processes in River Ecosystems. PHD thesis, Ghent University, Faculty of Engineering, 2009. 3.3 References 62

V.T. Chow. Open Channel Hydraulics. McGrawHill, New-York, 1959.

Y. Hai-long, X. Zu-xin, Y. Yi-jun. Eco-Hydraulics Techniques For Controlling Eutro- phication Of Small Scenery Lakes. A Case Study Of Ludao Lake in Shanghai. College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China. Shanghai Academy of Environmental Sciences, Shanghai 200233, China, October 2007.

Digital sources

DWAF Hydrology Online Database. http://www.dwa.gov.za/hydrology/cgi-bin/his/cgihis.exe/station

HBPD Remediation Program oﬃcial website. http://www.dwaf.gov.za/Harties/ ECOLOGICAL MODEL 63

Chapter 4

Ecological model

Before making an ecological model of the dam, an extensive literature study of what the problems and aims are, should be performed. Figure 4.1 shows perfectly why a well balanced ecosystem is of vital importance.

Figure 4.1: The environmental water balance (source: WRC) 4.1 Thermal stratiﬁcation in dams 64

4.1 Thermal stratiﬁcation in dams

During the summer the top water in a dam becomes warmer than the bottom water and as a result only the warmer top layer circulates, which does not mixed to any degree with the more viscous colder water, creating a zone with a steep temperature gradient in between, called the thermocline. The upper, warm circulating water is the epilimnion, and the colder, non circulating water is the hypolimnion.

During the summer of 1982 a surface temperatures of 28 ◦C with a corresponding bottom (25 m deep) temperature of 19◦C(ΔT=9◦C) has been recorded in the Hartbeespoort Dam. Such an situation is schematically presented in ﬁgure 4.2.

Figure 4.2: Conceptual depth/length proﬁle of a dam during thermal stratiﬁcation

With the onset of cooler weather, the temperature of the epilimnion drops until it is the same as the hypolimnion. During the 1981-1982 this temperature was measured as about 21.5 ◦C. This condition is known as the ’autumn overturn’ Under these conditions the water of the entire dam begins to circulate so that the temperature from surface to bottom is eventually more or less the same (21.5 ◦C).

As the temperature drops further, the colder surface water moves to the bottom while the warmer water from the bottom moves to the top. The lowest temperatures recorded during the 1981-1982 study were 15.5 ◦C on the surface with a corresponding bottom temperature of 13 ◦C (ΔT = 2.5◦C). 4.2 Trophic status 65

From the above it is clear that the temperature of the inflowing water will determine its flow- and mixing patterns within the dam. If the average temperature of the inflowing water is more than 15 ◦C in winter and more than 28 ◦C in summer, this water will tend to stay more within the warmer epilimnion than in the colder hypolimnion.

4.2 Trophic status

The word ’eutrophic’ comes from the Greek word eutrophos meaning well-fed. A widely quoted definition in South Africa is that ’eutrophication is the process of nutrient enrichment of waters which results in the stimulation of an array of symptomatic changes, amongst which increased production of algae and aquatic macrophytes, deterioration of water quality and other symptomatic changes are found to be undesirable and interfere with water uses. In essence, eutrophication is nutrient enrichment that causes problems. The following simplified definition is adopted:

Eutrophication is the process of excessive nutrient enrichment of waters that typically results in problems associated with macrophyte, algal or cyanobacterial growth.

Causes

In natural lakes a distinction is sometimes made between ’natural’ and ’cultural’ (anthropogenic) eutrophication processes. Natural eutrophication depends only on the local geology and natural features of the catchment. Cultural eutrophication is associated with human activities which accelerate the eutrophication process beyond the rate associated with the natural process (e.g. by increasing nutrient loads into aquatic ecosystems). In South Africa where most of the impoundments are man-made, the conceptual diﬀerence between ’natural’ and ’cultural’ seems less appropriate. Increased nutrient enrichment can arise from both point and non-point sources external to the impoundment as well as internal sources like the impoundment’s own sediments (that can release phosphate). Figure 4.3 illustrates some of the factors that drive the eutrophication process in an impoundment.

Eutrophication is a process and it is useful to be able to characterise the stage at which this process is at any given time in a particular water body. The ’trophic status’ of the water body is used as a description of the water body for this purpose. The following terms are used: 4.2 Trophic status 66

Figure 4.3: Simpliﬁed schematic illustration of the most important factors driving the eutrophication process.

• Oligotrophic: low in nutrients and not productive in terms of aquatic animal and plant life.

• Mesotrophic: intermediate levels of nutrients, fairly productive in terms of aquatic animal and plant life and showing emerging signs of water quality problems.

• Eutrophic: rich in nutrients, very productive in terms of aquatic animal and plant life and showing increasing signs of water quality problems.

• Hypertrophic: very high nutrient concentrations where plant growth is determined by physical factors. Water quality problems are serious and almost continuous.

It is convenient to associate the trophic status in impoundments with total phosphorus and chlorophyll a measurements. The relationships between trophic status and these variables are those of Van Ginkel et al. (2006), which were based on the work of Walmsley and Butty (1980) and Walmsley (1984). These have been shown to be applicable to South African impoundments. Phosphate rates are represented in ﬁgure 4.12.

Trophic status is therefore strictly related to one of the nutrients (namely phosphorus) and concentrations of planktonic algae and cyanobacteria (as chlorophyll a) (see table 4.1 and 4.2). Note that it is not necessarily directly related to concentrations of macrophytes or 4.2 Trophic status 67 algae attached to rocks and other surfaces. It is also possible to have a relatively high nutrient concentration and yet low plant growth (i.e. low chlorophyll a). For example, this can occur if light availability is reduced because of high levels of suspended solids or if high ﬂushing rates occur. Figure 4.4 shows clearly that zones with high chlorophyll a concentrate near the mouths of the Magalies River and CR. Figure 4.5 shows the current situation and target for the trophic status of the HBPD.

Table 4.1: Relationships between trophic status and monitoring variables.

Statistic Scheduled Sampling No. of records Value Mean annual chlorophyll a 26 24 77,02 μg/l Percentage of time chl a > 30 μg/l 26 24 > 50% Mean annual Total Phosphorus 52 50 0,122 mg/l

Table 4.2: HBPD current trophic status: hypertrophic

Impacts

Eutrophication is a concern because it has numerous negative impacts. The higher the nutrient loading in an ecosystem the greater the potential ecological impacts. Increased productivity in an aquatic system can sometimes be beneﬁcial. Fish and other desirable species may grow faster, providing a potential food source for humans and other animals (though this is not a common situation in South Africa). However, detrimental ecological impacts can in turn have other adverse impacts which vary from aesthetic and recreational 4.2 Trophic status 68

Figure 4.4: Chlorophyll-a distribution in the dam: the red zones are the high concentrations, the green zones the lower. to human health and economic impacts. This is summarised in the following ﬁgures (4.6 and 4.7).

Figure 4.6: Potential general negative impacts of eutrophication

• Ecological impacts: Macrophyte invasions and algal and cyanobacterial (blue-green) blooms are themselves direct impacts on an ecosystem. However, their presence 4.2 Trophic status 69

Figure 4.5: Current situation and target for the trophic status of the HBPD

causes a number of other ecological impacts. Of critical concern is the impact of eutrophication on biodiversity. Macrophyte invasions impede or prevent the growth of other aquatic plants. Similarly, algal and cyanobacterial blooms consist of species that have out-competed other species for the available nutrients and light. Their impact on animal biodiversity is also of concern. By generally lowering the ecological integrity of an ecosystem, only the more tolerant animal species can survive.

• Aesthetic impacts: Algal and cyanobacterial blooms, and particularly surface scums that might form, are unsightly and can have unpleasant odours. This is often a problem in urban impoundments where people live close to the aﬀected water body. If the water is being used for water treatment purposes, various taste and odour problems can occur. These lower the perceived quality of the treated water, although do not cause human health problems. 4.2 Trophic status 70

Figure 4.7: Schematic illustration of some speciﬁc impacts of eutrophication

• Human health impacts: an infestation of water hyacinth (Eichhornia crassipes) can be a health hazard. It can provide an ideal breeding habitat for mosquito larvae 4.2 Trophic status 71

and it can protect the snail vector of bilharzia. Of all the cyanotoxins currently known, the cyclic peptides represent the greatest concern to human health, although this may be because so little is known about the other cyanotoxins. The concern exists primarily because of the potential risk of long term exposure to comparatively low concentrations of the toxins in drinking water supplies. Acute exposure to high doses may cause death from liver haemorrhage or liver failure. Other short term effects on humans include gastrointestinal and hepatic illnesses. A number of adverse consequences have been documented for swimmers exposed to cyanobacterial blooms. Chronic exposure to low doses may promote the growth of liver and other tumours. Nevertheless, many cyanobacterial blooms are apparently not hazardous to animals. It is also possible that people exposed to odours from waterways contaminated with decaying algae of cyanobacteria may suffer chronic ill-health effects.

• Recreational impacts: The existence of large areas of macrophytes can inhibit or prevent access to waterways. This decreases the ﬁtness for use of the water for water sports such as skiing, yachting and ﬁshing. The presence of unsightly and smelling scums also makes any recreational use of the water body unpleasant.

• Economic impacts: Nearly all of the above mentioned impacts have direct or indi- rect economic impacts. Algal or cyanobacterial scums increase the costs of water treatment in order to avoid taste, odour and cyanotoxin problems in the treated water. Excessive blooms can clog ﬁlters and increase maintenance costs. Human and domestic and wild animal health impacts due to cyanotoxins in water have obvious direct economic impacts. Once signiﬁcant eutrophication has occurred, the costs of corrective action can be enormous. Macrophytes may need to be sprayed or brought under control by biological or other costly treatment processes.

The basis of eutrophication management is often the ’limiting nutrient concept’ (see also 4.2.4 - 4.2.8). The rate and extent of aquatic plant growth is dependent on the concentration and ratios of nutrients present in the water. Plant growth is generally limited by the concentration of that nutrient that is present in the least quantity relative to the growth needs of the plant. Minimisation of eutrophication-related impacts therefore tends to be focussed on eﬀorts to reduce nutrient (particularly phosphorus) inputs. This approach therefore deals directly with the primary cause of eutrophication (namely, nutrient enrichment). Typically, limiting nutrients entering an impoundment exhibiting a high degree of eutrophication will ﬁrst focus on point sources. These are easier to quantify, simpler to 4.2 Trophic status 72 manage and often contribute the highest nutrient load. Following this, non-point sources are managed and then internal (’in-lake’) management options can be implemented.

4.2.1 Hypertrophic dam

This dam is one of a number of hypertrophic dams in South Africa and has been in this state for some time. A hypertrophic dam means that the water is excessively enriched by phosphate and nitrogen nutrients, where algal growth is limited by solar radiation and water temperature. It occurs as a result of a combination of factors:

• Daily discharges from Waste Water Treatment Plants in the catchment (over 600 million litres per day).

• Stormwater ﬂows wash surface pollution such as sewer spillages, fertilizers, litter and animal waste into the dam.

• Phosphates (e.g. Washing powders)

• Poorly maintained sanitation systems that leak or overﬂow during rain storms.

• Stormwater increases into sewer networks that cause overﬂows into watercourses at manholes and pump stations.

• Informal washing in the rivers.

Toxic microcystis algal blooms and exotic water plants (hyacinths) form together with the bottom feeding fish a cycle of nitrogen and phosphorus recycling (see figure 4.8). Only way to break out of this spiral is to remove some of the components. In this case, there is the hyacinth and algae removal, bottom feeding fish is banned and sediments containing the nutrients will be dredged.

4.2.2 Algal bloom

When an ecosystem experiences an increase in nutrients, primary producers reap the ben- eﬁts ﬁrst. In aquatic ecosystems, species such as algae experience a population increase (called an algal bloom). Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water. Oxygen is 4.2 Trophic status 73

Figure 4.8: Nitrogen- cycle required by all respiring plants and animals and it is replenished in daylight by photosyn- thesizing plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to hypoxic levels, fish and other marine animals suffocate. As a result, creatures such as fish and especially immobile bottom dwellers die off.

The high level of nutrients in the dam, resulting in uncontrolled algal growth, occurs especially during summer months when solar radiation and the water temperature are high (ﬁgures 4.9 and 4.10). This serves as an important element in promoting algal growth. However, while the presence of algal growth is usually less during the cold winter months, it was still present in the dam-basin over recent winter months, probably a result of the global warming. There are examples of impoundments that have higher phosphate levels than Hartbeespoort Dam which do not have excessive algae. This is because they have healthy zooplankton such as Daphnia as well as shoreline vegetation. 4.2 Trophic status 74

Figure 4.9: Algal bloom during the summer of 2008

Figure 4.10: Algal distribution visible on satellite pictures

4.2.3 Cyanobacteria

Cyanobacteria (ﬁgure 4.11), also known as blue-green algae, require water, carbon dioxide, inorganic substances and light for their life processes. The term ’algae’ refers to micro- 4.2 Trophic status 75 scopic organisms, some of which form colonies. Cyanobacteria are organisms with some characteristics of bacteria and some of algae. They are similar to algae in size and, un- like other bacteria, they contain chlorophyll. Therefore, they are also termed blue-green algae, although they usually appear more green than blue. The growth rate of cyanobacteria is usually much lower than that of many algal species. Cyanobacteria can maintain a relatively higher growth rate compared to other phytoplankton organisms when light intensities are low. They will therefore have a competitive advantage in waters that are turbid due to dense growths of other phytoplankton. Maximum growth rates are attained by most cyanobacteria at temperatures above 25◦C.

Human activities, such as agricultural runoﬀ and sewage, have led to excessive increase of nutrients (eutrophication) in numerous water bodies. This has caused excessive algae and cyanobacteria blooms that considerably reduce the recreational values and usability of water as well as disturb the natural biological mechanisms in the water bodies. Originally livestock poisonings led to the study of cyanobacterial toxicity. As a result, a number of cyanotoxins have been now identiﬁed together with their mechanisms of toxicity.

Figure 4.11: Cyanobacteria

Toxic cyanobacteria are found worldwide in inland and coastal waters. Currently at least 46 species have been shown to cause toxic eﬀects in vertebrates. As research broadens, 4.2 Trophic status 76 additional toxic species are likely to be found. Therefore, it is prudent to presume a toxic potential in any cyanobacterial population. The most widespread cyanotoxins are microcystins and neurotoxins. The most common bloom-forming genus, Microcystis, are almost always toxic. Worldwide about 60% of cyanobacterial samples investigated contain toxins.

Cyanobacteria can form ﬂoating scums (like Microcystis), be distributed homogeneously throughout the epilimnion (like Oscillatoria) or grow on submerged surfaces. Cyanobacteria are particularly problematic because when their cells are ruptured (e.g. by decay or by algicides) they release cyanotoxins (copper-blue colour) into the water, though passive release can also occur. The in-shore deposits of cyanobacteria are often repulsive and potentially very toxic. For vertebrates, a lethal dose of microcystins causes death by liver necrosis within hours up to a few days. Some cyanotoxins are neurotoxic (target the nervous system) and others dermatotoxic (target the skin). A number of human deaths have been reported through exposure to cyanobacterial toxins. Observations of lethal poisoning of animals after drinking water with mass developments of cyanobacteria are numerous. The cases recorded include sheep, cattle, horses, pigs, dogs, ﬁsh, rodents, amphibians, waterfowl, bats, zebras and even rhinoceroses. Animals drink greater volumes of scum-containing water in relation to their body weight than humans, whereas accidental ingestion of algae by humans during swimming is a typical source of a lower dose.

Ecological impacts include various water quality impacts like increased cyanotoxin levels and lowering of oxygen levels (due to decay of algae and cyanobacteria). Decreased oxygen levels can have a number of other secondary water quality impacts. Anaerobic conditions allow reduced chemical species (like ammonia and sulﬁde) to exist. These chemicals can be particularly toxic to animals and plants.

4.2.4 Growth requirements of algae (and hyacinths)

All forms of life require a source of energy, a source of carbon and some essential mineral elements. In the case of blue green algae, which is a photo-autotroph, the energy source is light (radiation), the carbon source is carbon dioxide (or its salts- bicarbonates, carbonates) and the minerals are inorganic nitrogen (e.g. atmospheric nitrogen, ammonia, nitrites and nitrates) and phosphates.

For optimal growth, these growth requirements are required in a speciﬁc concentration (or intensity) ratio to one another. If the concentration (or intensity) of one of these 4.2 Trophic status 77 requirements is in a lesser ratio to the others than what is required for optimum growth, this growth requirement becomes the so called ’growth limiting’ growth requirement.

Any control of biological growth is thus aimed at making one (or more) essential growth requirements a growth limiting requirement.

4.2.5 Light as a growth limiting requirement

Turbidity when caused by clay and silt particles is often important as a light limiting factor. When turbidity is the result of living organisms, measurements of transparency become indices of productivity.

The euphotic zone depth (the depth at which 1% of the photosynthetically available radiation remained) is indicated in the top of ﬁgure 4.2. The depth of this zone ranged between 0.45 and 8.4 m (average 3.9 m in 1983/1984) for Hartbeespoort Dam. During this study, light conditions in the dam were usually best in Augustus-September and worst in January-February which coincided with the wax and wane of the algal population.

Presently, when the temperature of the inﬂowing Crocodile River water is similar (or higher) than the temperature in the euphotic zone, this plant nutrient rich water will not mixed with the bulk of the dam water, but will continuously replenish the water in the euphotic zone where the light conditions are favourable for algal growth.

One possible solution for controlling the hyper eutrophication in the dam would thus be to limit the replenishment of the whole epilimnion(and thus the euphotic zone) with incoming plant nutrient rich inﬂow, thereby limiting the plant nutrients available for algal growth to only those nutrients naturally present in the epilimnion.

4.2.6 Carbon dioxide as growth limiting requirement

Blue green algae are free ﬂoating cells within the water body. These algae can get its carbon requirements from the carbon dioxide normally present in the atmosphere (about 380 volume parts per million) and from the dissolved carbonate species in the water. The latter is continuously replenished by the microbial decomposition of settled biomass (sludge), present mostly in the anaerobic zone of the dam. The decomposing sludge layer is replenished every year by the die-oﬀ of biomass produced in the euphotic zone. 4.2 Trophic status 78

Since carbon dioxide and its chemical species are omnipresent, carbon dioxide as growth limiting requirement in a water column in the dam can only be limited by limiting the surface area exposed to the atmosphere and by annually removing the decomposing settled organic sludge layer produced in that particular water column.

4.2.7 Nitrogen as a growth limiting requirement

Many blue green algae species (but not Microcystis) are capable of ﬁxing atmospheric nitrogen in the absence of chemically bounded nitrogen. Practically it would thus not be possible to make nitrogen a growth limiting requirement in an open body of water exposed to the atmosphere.

4.2.8 Phosphorus as growth limiting requirement

From all the essential growth requirements for algae, phosphorus is the only one that is not freely available from the atmosphere. It would thus be logical to try and make phosphorus the growth limiting requirement for the control of algal growth.

Phosphorus can exist in water soluble form (mostly as ortho-phosphate) and as various insoluble forms. In the inﬂow to the dam the insoluble forms are usually associated with inorganic suspended solids (sand and silt) and in the dam self, with growing and settled biomass. Soluble phosphate in the inﬂow is mainly from treated sewage origin.

Phosphorous is the largest form of nutrients: since the 1970’s, high external nutrient loads are supplied by the Crocodile River. From the 1990’s on, there is a small decrease in nutrient loads (product with high phosphorous rates are being prohibited).

• Current inﬂow of P Load: 150 - 200 tons P/year (> 99% via Crocodile River), 3-4 times bigger than required

• Current Outﬂow: 90 - 110 tons P / year (some say only 30 tons P / year)

• The difference between the inflow and outflow accumulates either as insoluble pre- cipitates (organic and inorganic, about 31 tons) or as floating biomass and soluble phosphate (about 20 tons)).

• P suits to Blue Green algae growth 4.2 Trophic status 79

• Big Internal Nutrient Load (85 years of nutrients accumulation)

• Huge primary Production (10 000 - 15 000 tons biomass a year)

Distribution:

• Water Body: 50 - 70 tons P

• Sediments (total): 2500 - 3500 tons P

• Active Layers: 750 - 950 tons P

• Biomass: 80 - 120 tons P

Sediments hold the biggest part of P load. Note that in deeper layers, phosphorous is geochemically bound(irreversably bound), in the top layers, it is loosely bound.

• Total: 2 800 - 3 500 tons P

• Dam Wall Zone: 750 - 950 tons P

• Top layer (Active): 700 - 900 tons P

• Jelly (buoyant) Layer: 42 - 70 tons P

During 1982 (Januari - December) the soluble phosphorus in the surface water of the Hartbeespoort Dam was more or less constant at about 400 μg/l. The following year (1983) this phosphorus concentration drops to about 200 μg/l during Feb.- Mar. before it increase to a high of > 1200 μg/l during September. The implementation of the 1 mg/l phosphorus concentration standard for treated sewage effluents has reduced the in-lake phosphorus concentration from about 500 μg/l to a value of 130 μg/l in 2004. This is an important finding since it shows that if the inflow phosphorus concentration is reduced, it has a marked concentration diminishing (-74%) effect on the soluble phosphorus in the water phase of the dam.

Since 2004 however, the concentration of phosphate in the Crocodile River has increased to such an extent that the average ortho-phosphate concentration for the period January 2006 to March 2007 was 343 μg/l, very similar to what it was before the new phosphate standard of 1000 μg/l was enforced. 4.2 Trophic status 80

Figure 4.12: Hartbeespoort Dam total phosphate mass

The 2004 study shows that the soluble phosphate concentration (especially present in the euphotic zone) should be reduced to between 30 and 50 μg/l in order to have acceptable and manageable levels of blue green algae.

Consequently, if phosphorus is to be made the growth limiting requirement, the present average phosphorus concentration of > 343 μg/l should be reduced by more than 80% to bring the P concentration in the 30 to 50 μg/l range required. Nevertheless, from the diﬀerent algal growth limiting requirements available, the reduction of phosphorus concentration seems to be the most practical of all. 4.3 Ecological status of the Upper Crocodile Catchment 81

4.3 Ecological status of the Upper Crocodile Catch- ment

The ecological status (EcoStatus) of a river refers to its overall condition or health, i.e. the totality of the features and characteristics of the river and its riparian areas, which manifests in its ability to support a natural array of species. This ability relates directly to the capacity of the system to provide a variety of goods and services.

Figure 4.13: Habitat integrity and the biological response indicators

The integrated response of the habitat to modiﬁcations and the response of the biota to this, determines the health of the surveyed rivers. The outcome of this overall assessment will be referred to as the EcoStatus and comprises six indicators(ﬁgure 4.13 and 4.14), namely:

• Instream Habitat Integrity: This encompasses considerations of the severity of impacts on instream features such as the modification of the volume of water, a change in the flow regime (i.e. natural flow patterns), bed and channel modification, water quality, alien water plants, alien fauna that influences habitat directly and waste disposal. 4.3 Ecological status of the Upper Crocodile Catchment 82

• Riparian Zone Habitat Integrity and Riparian Vegetation Integrity: This considers the severity of impacts on riparian features such as the modification of the volume of water, a change in the flow regime (i.e. natural flow patterns), channel modification, water quality, reduction in vegetation and invasion by alien plants.

• Fish Assemblage Integrity: Fish are relatively long-lived and are good indicators of the longer-term changes in the condition of river habitats. These changes may be in response to alteration in river ﬂows, changes in river structure or changes in the chemical composition of the water.

• Macro-invertebrate Integrity: Aquatic macro-invertebrates include beetles, mus- sels, snails, crabs, worms and insect larvae. These organisms have relatively short life cycles therefore are good indicators of changes in water quality and habitat conditions over the short term.

• Water Quality: Diatoms were used to support the assessment of water quality. Diatoms are unicellular algae with their cell walls made of silica. A typical diatom community consists of a myriad of species, each with its unique shape. Each species has a speciﬁc water quality preference and tolerance.

The river health categories and their relation to the water resource classiﬁcation system as proposed by the Department of Water Aﬀairs and Forestry are presented in table 4.3. Figure 4.15 represents the ecological status of the Upper Crocodile Catchment.

Figure 4.14: Symbols representing the six indicators 4.3 Ecological status of the Upper Crocodile Catchment 83

Table 4.3: The river health categories

Figure 4.15: Ecological status of the Upper Crocodile Catchment 4.3 Ecological status of the Upper Crocodile Catchment 84

The overall EcoStatus of the Crocodile (West) Marico WMA is poor, with 13 of the 23 units surveyed classiﬁed as poor (see annex A). This WMA is highly developed: about 25% of the Gross Domestic Product of South Africa originates from the Crocodile (West) Marico. The industrial, mining and agricultural sectors within this WMA play a vital role in contributing to this economic achievement and are highly dependent on water resources within the WMA. Some parts of the WMA are still in good to natural condition. These are found primarily in the headwaters of catchments with very little development and human impact. Examples of river reaches in near pristine condition include the headwaters of the Groot Marico and Skeerpoort rivers.

4.3.1 Crocodile River

As mentioned before, sedimentation, urbanization, riparian vegetation destruction and toxic algae are the biggest problems in the rivers. Restoration of the upstream wetlands, riparian vegetation and in stream habitat, in combination with phosphate reduction, silt and erosion management and storm water management are the main aims to reintroduce a balanced ecosystem. Concrete measures that are considered: a pre-impoundment, a litter trap, dredging and river water treatment.

A litter trap at the inlet of the Crocodile River is being planned as part of the programme to collect litter transported with stormwater from urban and informal settlements and roads. Stormwater inlets and outlets from urban areas into the rivers also need to be equipped with litter traps.

Eutrophic state is the nutrient enrichment state of water that results in an array of stimulation of increased growth of biomass (algae and exotic water plants), deterioration of water quality and various other adverse consequences. Nutrient enrichment may occur through the use of waterborne sanitation, washing powder, fertilizer etc. Signiﬁcant reductions in surface water nutrient levels have been achieved in overseas countries by applying phosphate reduction initiatives. This project therefore aims to determine the feasibility of controlling nutrient sources i.e. phosphates and nitrates that exceed the threshold value and contribute towards increasing the level of eutrophication in the dam. The feasibility to actively promote the use of substitutions or alternatives to phosphorous in detergents in the geographical area of the upper Crocodile River catchment area can also be considered as well as improving the processing at the waste water treatment plants. 4.3 Ecological status of the Upper Crocodile Catchment 85

Wetlands Upstream

The wetlands project in the catchments of the Hartbeespoort Dam focuses on enhancing the functioning of the natural wetlands. It will also introduce artificial wetlands incor- porating the identification, mapping, assessing, monitoring, remediation and management strategies utilising best practices. It includes developing regulations to protect wetlands while implementing the water resources classification system in the catchment to protect riparian vegetation and aquatic ecosytems along the rivers.

Objectives:

• Protect natural wetlands

• Remediate impacted wetlands

• Construct Artiﬁcial Functional Wetlands (AFW)

• Increase biodiversity in catchment and reduce nutrient load by recycling nutrients

• Increase ecosystem services

Protection of natural wetlands:

• The identiﬁcation and preservation of natural wetlands in the catchment and around Hartbeespoort Dam which could play an important role in purifying the highly nutrient loaded from the receiving water within the rivers and streams that feed the Hartbeespoort Dam.

• Remediate those wetlands that are degraded (e.q. by erosion) to optimise their function ality in collaboration with Government Departments, landowners and Working for Wetlands.

• Replacement of alien invader vegeta tion and re-veqetanon with suitable indigenous plants.

• Develop Operational Best Practices as part of preservation strategies to mitigate the negative impacts from irresponsible and unsustai nable use for wetlands, watercourses, rivers and the associated riparian vegetation zones.

Artiﬁcial wetlands: 4.3 Ecological status of the Upper Crocodile Catchment 86

• The implementation of AFW mostly at point-source pollution sites as a polishing process.

• There are many different AFW designs including surface flow wetlands, sub-surface flow wetlands and typical reed-bed systems - each site warrants its own design depending on the intended requirements.

These actions in turn will reduce the amount of toxic algae and increase diversity mono- cultures such as the desired foodweb and biomass in the HBPD.

In-stream Habitat

Also important is the maintaining of the in-stream habitats of the rivers.

Objectives:

• Stabilize and improve the functionality of the In-stream habitat, the riverbanks and riparian vegetation zone to improve the:

– water quality, flow regime and biodiversity; – erosion control, storm-water reduction and dissipation – reduced sedimentation – reduced storm-water peak flows – recharge of ground water – stream bank, channel and floodplain stability; – aquatic habitat and aquatic biota; maintained base-flow and ground water recharge – water temperature and tight control (shading and lower light levels) and create micro clima te and habitat – filtration of nutrients, pathogens and toxins in runoff – habitat for wildlife: the life cycles of several species occur or rely on terrestrial riparian corridors for a portion of their life cycle or food.

• Create a vegetation ’bank’ to facilitate re-vegetation purposes in the bigger catchment 4.3 Ecological status of the Upper Crocodile Catchment 87

Functions and beneﬁts of wetfands and in-stream habitats

Wetlands through sediments and biomass trap nutrients in the water. This rich nutrient trap (wetland) import and exchange more nutrients from the surrounding environment and become a super recycler of nutrients through a high diversity food web. Wetlands exist in saturated, ﬂooded and waterlogged areas, either due to a high groundwater table or inundated by surface water for long enough to be unfavourable to most plants but favourable to plants adapted to anaerobic (no or very little oxygen present for use by plants and microbes) soil conditions.

Wetlands provide numerous immensely beneﬁcial and valuable eco-system services which are unique and inherent for people and wildlife including:

• Trapping and recycling nutrients and sed iments

• Cleaning, ﬁltrating and purifying the water

• Storing (like a sponge) and slowing ﬂoodwaters

• Maintaining surface water ﬂow

• Wildlife habi tat and biological productivity

Shoreline/riparian vegetation serves vital functions for the protection and maintenance of diversity of water qual ity thereby performing beneﬁcia! and valuable ecosystem services including:

• Filtration and reduction of sediments, nutrients, pathogens and toxins in runoﬀ

• bank stability

• reduction of erosion etc

Jukskei - Hennops Catchment

The overall ecostatus of the Jukskei - Hennops Catchment (figure 4.16) is poor and comprises the following indices: The instream habitat integrity is poor because of urban development. The majority of the river is canalised, urban runoff is high because of paved areas and sewage spills and industrial discharges are common because infrastructure can 4.3 Ecological status of the Upper Crocodile Catchment 88 not cope with the high levels of utilisation. It must be mentioned that some of the tributaries feeding the Crocodile River are not as severely impacted. The riparian zone habitat integrity is also poor primarily because the river has been engineered and the flow patterns completely altered. Riparian vegetation integrity is poor: natural vegetation has been completely altered because of urbanisation, and encroachment by poplar species is severe.

The fish assemblage integrity is poor: increased flow volumes and increased peak flows after heavy rains because impervious surfaces have altered natural flow regimes. There is complete loss of sensitive species and even hardy species have lowered frequencies of occurrence. Macro-invertebrate integrity is also poor: diversity and abundances are severely impacted by urban runoff including sedimentation, sewage flows and industrial discharges. Water quality is poor with high levels of nutrients and an increased frequency of water quality problems. The percentage of species tolerant to organic pollution indicates that the water is free from significant organic pollution. Water quality in the urban areas is severe, mostly because of sewage spillages and industries discharging into the sewer network. The sewerage system is not able to cope with the increase in housing density.

Figure 4.16: The Jukskei River near Vlakfontein

Some important drivers of change are:

• Urbanisation: impervious surfaces, lack ofsufficient capacity of sewer system, channel and flow modification 4.3 Ecological status of the Upper Crocodile Catchment 89

• Increased change of land-use from natural to urban and industrial

The following management responses are necessary:

• Upgrade sewerage system and improve management

• Reduce pollution from sewers, illegal discharges and reduction of instream solid waste (litter)

• Manage surface stormwater runoﬀ at source

• Clear alien invasives from riparian zone

• Encourage inﬁltration by reducing impervious surfaces to aid ﬂood attenuation

Crocodile - Rietvlei Catchment

The overall ecostatus of the Crocodile - Rietvlei Catchment (figure 4.17) is poor and comprises the following indices: instream habitat integrity is poor. This can be attributed to the severe modifications to the channel morphology and flow patterns. Patterns have changed because of development, an increase in return flows resulting in higher peak flows, water being imported into the system and sewer discharges into the river. Solid waste in the form of general litter is problematic in the riparian zone and instream. The riparian zone habitat integrity is poor: the modifications of channel morphology and flow has had a serious impact on the riparian habitats; bank erosion and inundation of the riparian zone have all contributed to low scores. Riparian vegetation integrity is poor with alien vegetation encroachment and vegetation clearing both impacting on riparian vegetation integrity. The fish assemblage integrity is poor: there is a complete loss of sensitive species. Even hardy species are under stress with lowered frequencies of occurrence. Macro-invertebrate integrity is poor: reduced water quality and flow modifications due to urban and industrial runoff have a severe impact on invertebrates. Water quality is poor because flows have high levels of nutrients and water quality problems but are free from significant organic pollution. This is primarily the result of urban runoff and industrial discharges.

Some important drivers of change are:

• High levels of urbanisation - sewerage system unable to cope resulting in sewage discharges 4.3 Ecological status of the Upper Crocodile Catchment 90

Figure 4.17: Rietvlei river just past the Rietvlei Dam

• Discharges from industries into the sewer system

• Canalisation and alteration of ﬂow patterns

• Invasive alien plants in riparian zone and in catchment

The following management responses are necessary:

• Reduce and clean-up litter pollution

• Control of discharges into river - both sewage and industrial - to improve water quality

• Clear invasive aliens in riparian zone

Skeerpoort - Catchment

The overall ecostatus of the Skeerpoort Catchment, a small tributary of the Magalies River, is natural and good. It comprises the following indices: The instream habitat integrity is good: there are several dolomitic eyes at the source of the Skeerpoort River which are still in pristine condition. Some farming activities have impacted on flows lower down in the system. The riparian zone habitat integrity is good: there is very minimal 4.3 Ecological status of the Upper Crocodile Catchment 91 impact on the riparian zone with some localised bank erosion. The riparian vegetation integrity is fair, with alien vegetation encroachment having an impact at a small number of localities and some vegetation clearing for agriculture. Fish assemblage integrity is good to naural, with some impacts due to farming activities influencing fish diversity. Eels are lost due to obstructions, especially Hartbeespoort and Roodekopjes dams. Macro- invertebrate integrity is natural: macro-invertebrate diversity and abundance is high and close to natural conditions with species present that require permanent flows and high water quality conditions. Water quality is natural, flows have low to intermediate levels of nutrients and free from significant organic pollution. The result is that the Skeerpoort River, which is particularly located in a nature reserve, is one of the few tributaries of the dam, that are not contaminated. A drivers of change could be the farming activities, although they currently have minimal impact.

The following management responses are necessary:

• Restrict development to a minimum, as the greater part of the Skeerpoort catchment is situated within a proclaimed nature reserve

• Monitor farming activities: ensure impacts are minimal into the future

• Eradicate alien invasive plant species

Magalies - Catchment

The overall ecostatus of the Magalies Catchment (figure 4.18) is poor and comprises the following indices:the instream habitat integrity is poor. This is attributed to high levels of water abstraction primarily for bottling. Water abstraction by farmers is also high with 25 furrows on the Magalies River alone. Many people rely on the furrow water for domestic use. The Magalies River has it’s main source at Malony’s eye upstream from the town of Magaliesburg. A constant flow of water surfacing at Malony’s eye from the Steenkoppies dolomitic compartment feeds the river throughout the year. The riparian zone habitat integrity is also poor: furrows have resulted in inundation of the riparian vegetation and flow modification has altered natural riparian habitats. The riparian vegetation integrity is poor, with riparian vegetation being cleared for agricultural and housing purposes. Alien vegetation encroachment is serious. Fish assemblage integrity is fair: the upper reaches still sustain some sensitive species, while the lower sections are impacted by water abstraction 4.3 Ecological status of the Upper Crocodile Catchment 92 and flow modifications. Macro-invertebrate integrity is poor: overall, primarily because of water abstraction and therefore habitat alteration and some localised impacts on water quality from the town of Magaliesberg. Although in the upper reaches integrity can be classified as fair. The water quality is good, with localised impacts from lodge developments along the river and return flow from pig farms, chicken farms and flower farms in the area.

Figure 4.18: The Magalies River in the Magelies Nature Reserve

Some important drivers of change are:

• Serious encroachment of alien vegetation in the riparian zone

• High levels of water abstraction resulting in changes in the natural ﬂow regime of the river

• Large volumes of water extracted from the Steenkoppies/Holfontein compartment for agricultural use

• Flow regulating structures - large number of weirs for irrigation altering ﬂow patterns

The following management responses are necessary:

• Monitor and control water use and abstraction. Ensure that the ecological reserve is determined and maintained.

• Clear alien vegetation in the riparian zone

• Consider installing ﬁsh ladders in suitable ﬂow regulating structures 4.3 Ecological status of the Upper Crocodile Catchment 93

4.3.2 Dam basin: HBPD Remediation Program

Several studies clearly establish that Hartbeespoort Dam can be saved. However, there are no cheap, quick or easy ways to do this. Several issues have to be tackled at the same time in both water and land management. The solution is integrated catchment management that involves a large number of authorities and stakeholders from two provinces (Gauteng and North West Province). Also several national and provincial departments, municipalities and the private sector (particularly dwellers, property owners and the tourism industry around the dam) should participate in the management.

The Harties, metsi a me integrated biological remediation programme of the Department of Water Affairs (DWA) is being implemented by Rand Water. The implementation will take place in two phases over a period of time. Phase one focuses on establishing biological processes and mechanical harvesting of biomass (algae and hyacinths). Phase two will focus on the treatment and the bulk removal of phosphate.It comprises a number of projects which are interlinked and interdependent, each aiming to improve the water quality and biodiversity in the dam. This section focusses on two of these projects namely the development and maintenance of floating wetlands and the rehabilitation and management of the shoreline vegetation. These two projects should however be considered in conjunction with the fish removal and management; wetlands upstream; and the riverbank and in-stream habitat projects. In the catchment area, focus is on:

• Water quality management including reduction of fertilizer and pollution load from point and nonpoint sources within the catchment.

• Treatment of polluted incoming water before it enters the dam from the Crododile River.

• Recreational regulations for boating, angling and allowing public access.

• Public awareness and education programmes.

In the dam basin, the remediation is concentrated on biomass management. The ongoing actions are:

• Control and remove algae

• Control ﬂoating wetlands 4.3 Ecological status of the Upper Crocodile Catchment 94

• Shoreline vegetation

• Control hyacinths

• Sediment removal

• Fishery management and monitoring (biomanipulation)

Aim and objective of ﬂoating wetlands and shoreline rehabilitation

The aim of rehabilitating the shoreline and implementing floating wetlands, is to improve habitat conditions for the breeding and maintenance of zooplankton, invertebrate, insect, fish and birds populations. This will contribute towards improving the natural energy and nutrient flow in the food web and ultimately waterquality in Hartbeespoort Dam. These projects have the following objectives:

• Manipulate and increase the species’ diversity and obtain the desired food web structure through rehabilitation, restructuring, monitoring, maintenance and management.

• To establish a habitat which will increase the diversity of the aquatic biota within the water body and to create feeding and breeding habitat for ﬁsh, birds and other biota.

• To supplement shoreline/riparian vegetation destroyed in the construction of housing schemes, golf courses as well as boating and water sports facilities, etc.

• To provide a nursery facility for indigenous macrophytes for distribution to new wetlands being established in the dam and for distribution to other water bodies in South Africa with similar problems.

• To develop technology which will allow the establishment and management of ﬂoating wetlands of indigenous plants within the water body.

• To help stabilise water temperature along the shoreline.

• To minimise the eﬀects of erosion and wave action on the sediments near the shoreline (riparian and littoral zones).

• To reduce turbidity along the shoreline. 4.3 Ecological status of the Upper Crocodile Catchment 95

• To establish management protocols to eﬀectively manage ﬂoating wetlands.

• To act as a buﬀer zone between dry land and the areas which are usually inundated during the most of the year.

Floating wetlands create an enabling environment for zooplankton and other aquatic biota populations to grow and diversify and to restore the shoreline vegetation that will provide habitat for zooplankton and other organisms as well as a safe spawning habitat for desirable fish species in the dam. Use of natural vegetation in shoreline management zones and other soft shoreline protection options wilt further contribute towards habitat rehabilitation and protection and proper nutrient and energy flow. Rehabilitation of vegetation zones and the placement of floating wetlands in identified areas will also help with the nutrient assimilation in the dam as these plants will trap these nutrients in their tissue. In this way nutrients can then be removed from the dam by harvesting the plant biomass. This will also add to the reduction of nutrients and the effect of nutrient enrichment in Hartbeespoort Dam.

Shoreline Vegetation

Hartbeespoort Dam is an artificial impoundment with associated limitations. At present the shoreline of Hartbeespoort Dam covers a distance of approximately 56 km of which about 18 km have been permanently lost through property development activities and 20 km has no suitable buffer zone as a result of detrimental human activities (see figure 4.19). The remaining 18 km can possibly be re-established shoreline degraded to non-repair state environmentally acceptable possibility of shoreline rehabilitation A healthy aquatic ecosystem should be surrounded by a transition/buffer zone of a minimum of 10 metres in width (figure 4.20), which facilitates the change or transition from dry land/terrestrial plants and sub-aquatic vegetation to aquatic vegetation (i.e. the riparian and littoral zone respectively).

A bufferzone acts as a filter to trap nutrients and pollution from storm water prior to it reaching a water body and plants such as bushes, trees, shrubs and grasses (aerobic root system) can fulfil this role. However, plants that are needed between the buffer zone and the water should be able to grow in both dry and submerged conditions and they include sedges, reeds and rushes (aerobic and anaerobic root systems). 4.3 Ecological status of the Upper Crocodile Catchment 96

Figure 4.19: Status of the HBPD shoreline

The destroyed shoreline has had a detrimental effect on the critical biological/wetland activity which would normally take place within the transition/buffer zone (riparian and littoral) This has impacted negatively on the aquatic food web as the habitat for zooplankton and other aquatic epi- biota (i.e. aquatic biota associated with vegetation cover namely diatoms, invertebrates, molluscs, and fish) has been lost in the process.

Figure 4.20: Transitional/buﬀer zone between land and water

In order to address this situation, the following key interventions are necessary: • protecting the shoreline

• re-establishing shoreline vegetation where possible 4.3 Ecological status of the Upper Crocodile Catchment 97

• Rehabilitating the shoreline with artiﬁcial systems, such as ﬂoating wetlands close to shoreline areas that have been stripped of natural vegetation and where re-establishment of shoreline vegetation is not possible.

• To incorporate gravel and rock beds as these will assist to stabilise the bottom substrate. It serves as anchorage for plants and help to stabilise their root systems against erosion. It serves as a bio-ﬁlter, as a habitat or surface substrate for aquatic biota, to live and feed on and in- between the gravel and rocks.

Objectives:

• Develop a rehabilitation plan which includes:

– the most desirable indigenous plant communities – increase foraging and breeding areas for ﬁsh – manipulating the topography of the littoral zones to provide suitable habitats for the plant communities which will be established

• Stabilize and improve the functionality of the shoreline riparian vegetat ion zone - thereby improving :

– water quality – biodiversity – ﬂow regime – storm-water dissipation and erosion control

• Create wetlands habitats

• Improve ecosystem services

• Replicate wetland functions - to continuously keep nutrients recycled throughout the foodweb.

• Protect the wetlands, riparian vegetation and in-stream habitat at HBPD.

• Incorporation of bioremediation, phytoremediation and hyperaccumulation principles. 4.3 Ecological status of the Upper Crocodile Catchment 98

The easiest and most economical way to replace totally degraded shoreline is to establish substitute areas of plant biomass in the shallower areas of the dam (figure 4.21). Through this process significant numbers of diverse aquatic plants will be planted in areas which are up to one meter deep during most of the year. These newly ’created’ wetland areas will be made accessible to the public for a variety of activities e.g. bird watching, fly fishing, etc.

Figure 4.21: Improved/artiﬁcially enhanced shoreline conditions

Once established, plants will have to be managed on a sustainable basis which will mean harvesting excessive biomass during dormant growth periods. This harvested biomass will be put to sustainable use depending on the nature of the plant. It could be used for composting, the manufacture of a variety of products or even eco-friendly building materials. Figure 4.22 shows the development of the riparian zone between 2005 and 2008.

The aquatic vegetation in the littoral zone serves as:

• living surface for organisms to attach to such as diatoms and algae

• feeding surface where ﬁsh and invertebrates can feed on the algae and diatoms from the plant sterns, roots, and leaves

• breeding habitat for ﬁsh and other biota

• nursery area for ﬁsh fry and protection in terms of cover

• bio-ﬁlter to help trap nutrients 4.3 Ecological status of the Upper Crocodile Catchment 99

Figure 4.22: Small bay at the Caribbean Beach Club golf course in 2005 (up) and 2008 (below)

• stabilise the banks in terms of erosion and nutrient re-suspension back into the water column due to wave action.

Floating Wetlands

A floating wetland is an artificial structure constructed from natural materials such as bamboo or Spanish reed and which is designed to contain and support indigenous water plants in areas where shoreline vegetation cannot be replaced and to provide replacement of shoreline vegetation when the dam is at lower levels. The root systems of the plants in the artificial wetland will provide a habitat for zooplankton, macro-invertebrates, fish and other aquatic organisms while the above surface growth provides a habitat for insects, birds, reptiles and other mammals (figure 4.23).

The use of floating wetlands is relatively new in South Africa and trials have been conducted to determine which plants will float and grow in a floating wetland without any supporting substrate. The idea is that floating wetlands will act as an important link and support to related projects such as the restructuring of the fish population and the entire food web as well as the restoration of shoreline vegetation. These wetlands can be strategically placed close to the shoreline thereby improving local biodiversity and overall water quality. The 4.3 Ecological status of the Upper Crocodile Catchment 100 alternative to floating wetlands would be to create more plant biodiversity within the dam basin and riparian zone.

Figure 4.23: Floating wetlands food web

Objectives:

• Achieve increased zooplankton populations and diversity.

• Create a habitat for zooplankton and small ﬁsh.

• Allow for the establishment of macrophyte biodiversity within the water body.

• Establish a habitat which will encourage the development of macroinvertebrate diversity within the water body thus creating food for ﬁsh and birds.

• Possible breeding and shelter for ﬁsh spawn.

• Stabilize water temperature along the shoreline.

• Function as energy breakers for water action to reduce turbidity along the shoreline.

• Develop technology which will allow the establish ment and management of ﬂoating wetlands of indigenous plants within the water body. 4.3 Ecological status of the Upper Crocodile Catchment 101

• Supplement for shoreline/riparian vegetat ion destroyed in the construction and development of housing schemes and golf courses.

• Provide a nursery facility for indigenous macrophytes for distributing to new wetlands being established in the dam and for distribution to other water bodies in South Africa with similar problems.

Figure 4.24: Wetlands planned around the dam (source: Google Earth and HBPD Remediation Project)

Various types and designs of floating wetlands were piloted or tested (figure 4.25). However the design of the floating wetlands used in Harties, Metsi a Me contain plants within a medium which can be moved easily should water levels drop and the littoral zone (shoreline) becomes dry. Various products have been tested to determine the most viable and affordable method of producing floating wetlands. The ideal seems to be Spanish reed (also known as common giant reed), an exotic plant, which also has to be eradicated and is being removed from the shoreline of the dam. 4.3 Ecological status of the Upper Crocodile Catchment 102

Figure 4.25: Floating wetlands on the HBPD

The following design criteria are being used:

• The plants and construction materials must have a natural buoyancy to ensure permanent ﬂoating (or artiﬁcial buoyancy needs to be added).

• It must serve to contain as much biomass as possible in terms of area.

• It should provide a proper interface with the dam such as to allow maximum habitat establishment in and on top of the water.

• It must be mobile and transportable on the water surface.

• The biomass within the ﬂoating island must be accessible from all sides to facilitate harvesting and general management and monitoring.

• It must be ﬂexible enough to conform to existing shoreline geometry in places where riparian vegetation has been irreparably destroyed.

• It has to facilitate ease of monitoring and management.

• It should develop into permanent islands that last for years, preferably indeﬁnitely.

The prototypes of floating wetlands are at present being built at the Kommando Nek Nature Reserve and Kurper Oord to allow for comparative monitoring between floating wetland structure types, plant types and surface area size. Preliminary monitoring of zooplankton and macro invertebrates within floating wetlands has given very positive in- dications of a successful process. Other areas where the floating wetlands are being implemented are at strategic points such as water abstracting points (e.g. Schoemansville), river entrances (e.g. Swartspruit, Leeuspruit, Magalies River, etc) and within estates with owners taking ownership and maintenance of the wetlands (figure 4.24). 4.3 Ecological status of the Upper Crocodile Catchment 103

Fishery management and monitoring: commercial ﬁshery and food web(Zooplankton)

Fishing is one of the popular recreational activities at Hartbeespoort Dam. The fish community of the Hartbeespoort Dam consists of fourteen species. However the current fish numbers and biomass are dominated by exotic and undesirable fish species. These are: catfish (over 70% of the fish biomass), canary kurper (50% in tems of numbers), the Mozambique tilapia (over 25% in tems of numbers) and carp. They are detrimental to the functioning of the aquatic ecosystem. They contribute to maintaining the distorted conditions in the dam, and to the destruction of aquatic plants (especially carp), which in turn eliminates aquatic vegetated habitat. Without suitable habitat certain organisms cannot reproduce and effectively perform their role in the food web and ecosystem. The undesirable fish species also rely heavily on zooplankton as a food source, which impacts on the zooplankton population and its grazing potential as primary consumers, thereby influencing the natural nutrient and energy flow in the dam. The carp and catfish are also responsible for bio-turbation and resuspension of nutrients back into the water column due to their benthic feeding behaviour (foraging in the bottom sediments), making these nutrients available for algal growth. The fisheries project that involves establishing a fishery, monitoring and management of the fisheries and restructuring the fish population and the food web in the dam.

Figure 4.26: Catﬁsh (left) and carp (right) should be targeted as part of the ﬁsheries management.

The proposed rehabilitation plan of Hartbeespoort Dam includes large-scale removal of the coarse fish (e.g. carp and catfish) populations. This is intended to offset topdown grazing on the plankton of the reservoir. Th most important mean is to restructure the fish community for removing algae and improving economical values on the basis of recent 4.3 Ecological status of the Upper Crocodile Catchment 104 large-scale biomanipulations. The following guidelines regarding when, where and how the fish community should be restructured, are proposed.

• Reduction of the biomass of coarse ﬁsh feeding on plankton should be 75% or more. In HBPD this is applicable to canary kurper, catﬁsh and carp.

• The ﬁsh reduction should be performed rapidly in a short period of time.

• The number of young ﬁsh should be reduced. In HBPD the catﬁsh and carp will be targeted.

• The external nutrient load should be reduced as much as possible before initiating biomanipulation.

• Shoreline habitats in the water should be restored for providing breeding grounds and shelter for desired ﬁsh species. Also ﬂoating wetlands should be introduced.

In order to achieve the desired effects, it is recommended that the fish community is restructured by removing 200-300 tonnes of coarse fish (carp and catfish - figure 4.26) during the first years. This will cause natural shift towards Mozambique tilapia becoming the most important species. As a result, it can be exploited as table fish. The shift towards the Mozambique tilapia is highly desirable for both economical (see below) and ecological reasons, since the species is also an algal feeder. Introduction of any other species is unnecessary, as the Hartbeespoort Dam has all the elements of a successful fishery.

Recreational Regulations

Today, no speciﬁc regulations exist for recreational use of the dam and no oﬃcial body is responsible for policing and monitoring of the various water sport and leisure activities. The possibility of zoning the dam for various recreational and protection uses should be investigated.

• Boating regulations are needed for regulating the use of all water vehicles for safety and environmental reasons.

• Fishing regulations are necessary for governing angling in the dam, which also supports the biomanipulation of ﬁsh community. 4.4 Model 105

• Public access is limited to a small stretch on the shoreline of the southern part of the dam, which may soon be closed by private development. It is important to assure continued public recreational access, by public lands, on the shores of the dam reservoir.

Public Awareness and Education

Increasing public awareness by oﬀering information and education in the Hartbeespoort Dam area is important. Brochures, pamphlets, public information events and workshops need to be produced for the stakeholders and communities. Also visitors need to be included in the awareness raising.

4.4 Model

The ecological moddeling will only be started after completion of the hydraulic modelling. It will be develloped in the future. An overview of the available data, necessary to build the model, is included on the CD. It consists of weather data (temperature, sunlight, wind) and water quality data (pH, P- concentration, N- concentration, dissolved oxigen level, radioactivity,...).

4.5 References

Literature

B. Harding. Hartbeespoort Dam: An Action Plan. Water Wheel Magazine, 2004 Volume 3 No 6 November/December, pages 6-10.

C.E. van Ginkel, B.C. Hohls, E. Vermaak. A Ceratium hirundinella bloom in Hartbeespoort Dam, South Africa. Institute for Water Quality Studies, DWAF, December 2000. 4.5 References 106

C.E. van Ginkel, M.J. Silberbauer, S. Du Plessis, C.I.C. Carelsen. Monitoring microcystin toxin and chlorophyll in ﬁve South African impoundments. Verh. Internat. Verein. Limnol. Stuttgart, March 2006.

D.C. Grobler, M. Ntsaba. Strategic Framework for National Water Resource Quality Monitoring Programmes. Report No. N/0000/REQ0204 - Resource Quality Services, Department of Water Aﬀairs and Forestry, Pretoria, South Africa, 2004.

E.P. Odum. Fundamentals of Ecology. 3rd Edition W.B. Saunders Company, 1971.

Factsheet: Wetlands for life. Harties, Metsi a me Integrated Biological Remediation Pro- gramme, October 2009.

Factsheet: Wetlands and Shoreline Vegetation. Metsi a me Integrated Biological Remedi- ation Programme, August 2009.

Guidelines for safe recreational water environments (Volume 1): Coastal and fresh waters; Chapter 8: Algae and cyanobacteria in fresh water. World Health Organisation, 2003.

J. Kruger. Presentation: Hartbeespoort Dam Remediation Programme - Biological Reme- diation - Local ﬁnancing solutions. ICA Conference, Dakar 26-27 November 2008.

K. Soetaert, V. deClippele, P. Herman. FEMME, a ﬂexible environment for mathematically modelling the environment. Ecological Modelling, Volume 151, Pages 177-193, 2002.

L. De Doncker. A Fundamental Study on Exchange Processes in River Ecosystems. PHD thesis, Ghent University, Faculty of Engineering, 2009.

P. J. Oberholster, A. M. Botha, T. E. Cloete. An overview of toxic freshwater cyanobacteria 4.5 References 107 in South Africa with special reference to risk, impact and detection by molecular marker tools. Nigerian Society for Experimental Biology, May 2005.

P. Venter. Presentation Harties - Metsi A Me Remediation Programme: An integrated biological remediation management approach at the dam. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

T. Boshoﬀ. North West Environmental Management Series 5: Dam Remediation Hart- beespoort Dam. North West Provincial Government Maﬁkeng, South Africa, 2005.

W.A. Pretorius. Pre-impoundment - begroting. Report DWAF, July 2007.

W. McKibben. Carbon’s New Math. National Geographic. October 2007.

W. R. Harding. The Determination of Annual Phosphorus Loading Limits for South African Dams. WRC Report No 1687/1/08, February 2008.

W.R. Harding, J.A. Thornton, G; Steyn, J. Panuska, I.R. Morrison, Hartbeespoort Dam Remediation Project (Phase 1) - Volume I - Action Plan. NWP Dacet, DH Environmental Consulting, October 2004.

W.R. Harding, J.A. Thornton, G; Steyn, J. Panuska, I.R. Morrison, Hartbeespoort Dam Remediation Project (Phase 1) - Volume II - Action Plan. NWP Dacet, DH Environmental Consulting, October 2004. 4.5 References 108

Z. Cukic. Presentation Hartbeespoort Dam: Internal Load Issues. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

Digital sources

Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Eutrophication

Factsheet cyanobacteria. HBPD Remediation Program, May 2007. http://196.3.165.92/hartiesdev/factsheets/Cyanobacteria22May07.pdf SOLUTIONS 109

Chapter 5

Solutions

The HBPD Remediation Program worked out a program of ”Water Quality Management” (ﬁgure 5.1). The overall aim is to reduce external pollution by 60% from the current levels, which requires managing several pollution sources simultaneously as described in previous chapters. As proven in 4.2.8, most of the attention should go to the reducing of the phosphorus concentration. In ﬁgure 5.1, an overview of all considered alternatives is represented.

Figure 5.1: Overview of the HBPD Remediation Program 5.1 Short- term solutions 110

Table 5.1: Alternatives for the HBPD

5.1 Short- term solutions

In the short- term, one of the most important things to do is to make people aware of the problem and convince them that everybody could contribute to solve the problem. As mentioned in paragraph 4.3.2, recreation regulations and public awareness and education are main things the people can play a role in.

The Hartbeespoort Remediation Program has already set up some eﬀective, short- term solutions. Below, the most important ones are mentioned. 5.1 Short- term solutions 111

5.1.1 Fishery management and monitoring

As already discussed in paragraph 4.3.2, fishery management will contribute to the restoration of the ecological equilibrium. The unwanted bottom feeders, causing the reentering of contaminations, together with the fish destroying the zooplankton population should be removed. The fishery management also includes a lot of job creation in the region.

5.1.2 Control and algae removal

Floating booms are used to assist with the surface movement concentration and physical removal of algae from the water. Four to ﬁve positions for boom placement have been identiﬁed, one of which has already been placed successfully at the dam wall as a proto- type. Compost will be produced from the harvested algae and hyacinth. The composting combined with the removed sediment will produce a high quality soil conditioner.

5.1.3 Control hyacinths (harvesting and composting)

Similarly to algae, hyacinths will also be removed from the water by concentrating the movement of these water plants on the dam (ﬁgures 5.2, 5.3 and 5.4). Hyacinths may possibly be used as plant material in the ﬂoating wetlands which has to be harvested on a regular basis.

5.1.4 Sediment removal

Treatment of water flowing into the dam will hardly change the appearance of the water unless sediment can be cleared of its high nutrient levels. As the sediments contain so much nutrients, the challenge is to dredge this top layer and find a beneficial use for it. The nutrients trapped in the sediment render it up to ten times more productive than arable land. One possibility is to use it for the rehabilitation of land that has been rendered sterile by mining operations. It could also be used with other biomass from the dam in the production of compost for agriculture and horticulture and the general improvement of soil quality. It could even be used in the production of bricks. There are several ways in which sediment can be dredged, but considerable infrastructural development will be necessary before dredging on a commercial scale could be effected. 5.1 Short- term solutions 112

Figure 5.2: Massive growth of hyacinths

Figure 5.3: Harvesting hyacinths

Figure 5.4: Composting the hyacinths 5.1 Short- term solutions 113

A pilot project for the harvesting of the jelly (gelatinous buoyant) layer is due to be commissioned shortly and will involve an experimental plant employing the suction method of dredging from Oberon. That is close to the area where sediment is deposited as the Crocodile river enters the dam. A suction plant could also be operated from the dam wall to harvest the jelly layer that has been deposited there.

A major challenge in the disposal of the sediment will be the transport of the material. Transport costs would be prohibitive, but can be reduced by getting rid of most of the water and reducing the sediment to solids as far as possible. From the processing plant the sediment can be transported by road to the disposal sites, whether mining rehabilitation sites, agricultural operations or other applications. The principle objective of the project is to ensure that:

• Reduce Internal Nutrients Load and Nutrients Recycling

• Dredging of incoming sediments is feasible.

• Support eﬀorts to shift Dam trophic level from hyper-eutrophic to meso-eutrophic

• Recover a part of Dam’s working volume

• Removed sediments are re-used economically and in an environmentally safe manner.

• Source willing local partners to use material: removed sediments are used with compost production or other applications such as rehabilitation of depleted soils, which might also include household, agriculture or mining.

• Jobs creation - removed sediments processing and use

Distributed mostly along natural beds of rivers and basin, an area of 450 - 500 ha is covered with sediments (ﬁgure 5.5). The total volume involves 30 - 35 x 106 m3 of sediments:

• Main Basin: 25 - 28 x 106 m3

• Dam Wall zone: 2.5 - 3.5 x 106 m3

• Others: 2.5 - 3.5 x 106 m3

• Depth: 4m - 18m (Dam Wall zone) 5.1 Short- term solutions 114

Figure 5.5: Major sediment zones in the dam reservoir

For the 80 year average, the volume of the dam decreases by 0.24% per year. The average height growth rate is about 10 - 15 cm per year, but slowing down. The volume of active sediment layers is for the moment 3.0 - 3.5 x 106 m3. The volume of jelly (buoyant) layer amounts to 1.0 - 1.5 x 106 m3.

The following lab analyses data on the sediment is available:

• General parameters: pH, Dry solids, Density, COD

• Plain Nutrients: N Forms, P forms, Carbon

• Specials: Oil & Grease, Surfactants

• Anions: Sulphate, Chloride, Fluoride, Sulphide

• Cations: Ca, Mg, K, Na, Si, Fe, Mn, B, Se, Al, Cu, Zn, Ni, As, Cd, Hg

• Gross β radioactivity

• Bio-Agents: Helminth Ova, HPC, Tot. Coli, E. Coli 5.1 Short- term solutions 115

The main results are (see also ﬁgure 5.6):

• Dry solids: 25% - 65% (mostly 30 - 35%)

• Density: 1.18 - 1.45 t/m3

• P content: 0.45 - 0.95 gP / kg DS

• N content: 2 - 4 gN / kg DS

• C content: 30 - 40 gC / kg DS

• Jelly Layer density: 1.11 t/m3

Note that there is a signiﬁcant diﬀerence between sediments in Magalies basin and Main basin.

Figure 5.6: Loads of the sediment 5.1 Short- term solutions 116

Sediments/mud volumes to be dredged :

Jelly Layer 1.0 - 1.5 x 106 m3 Sediments (active layer) Main Basin 3.0 - 4.0 x 106 m3 Sediments (active layer) Dam Wall 0.5 - 0.8 x 106 m3 Sediments (active layer) Magalies 0.4 - 0.6 x 106 m3 Total Volume of sediments to be dredged 4.9 - 6.9 x 106 m3

Remark that real volumes (mud/water mixture) should be increased for 25 - 35%. Appli- cable dredging techniques:

• Hydraulic i.e. Suction (Jelly Layer)

• Mechanical - Suction Cutter head (Sediments)

• Combined (Dam Wall Zone)

As part of the HBPD remediation program, the top priorities are to dredge the jelly layer and the sediments in the main basin (see figure 5.5) and around the dam wall. Secondly, dredging operations will start in the Magalies confluence area and Crocodile River confluence area.

Figure 5.7: Near the conﬂuence of the CR and the HBPD, a lot of sedimentation occurs 5.1 Short- term solutions 117

Period Water (m3) Sediments (m3) 1923 226 x 106 - 1990 201 x 106 27-30 x 106 2007/2008 195 x 106 30.5 - 36 x 106

Table 5.3: Sediment contents

5.1.5 Chemical ﬁxing of the phosphorus in the Crocodile River

It is possible to chemically fix the phosphorus of the total Crocodile River inflow. For an 80% removal efficiency of phosphorus with ferric sulphate (6 mg Fe/l) as flocculent, the estimated cost in 2004 was R6.5 million per annum (650 000 Euro).

Apart from the fact that the dosing of a dosing of a chemical has the same reliability drawbacks than the operation of a sewage works, is it just not wise from a water quality point of view to exchange one chemical (phosphorus) for another chemical (sulphate).

Chemical fixation of phosphorus is a possible option, but because of problems associated with flocculent availability, reliability of dosing, and costs, chemical fixation should be considered in conjunction with other phosphorus removal methods.

5.1.6 Others

Other short- term measures could include:

• Investigate the bottom (sediment) to assess remediation of the sediment in the dam. This produces information on the phosphate release rate and possible heavy metal concentrations in the bottom of the dam reservoir.

• Improve management of urban and farming activities for decreasing fertilizing runoﬀs from the streets and agriculture. Farmers need guidance in erosion control measures.

• Organize regular monitoring for microcystin levels to ensure public safety and publish the results.

• Organize long-term monitoring for following the response of the reservoir to the interventions. Design and conduct further pilot studies and ﬁshery studies in accordance with the agreed monitoring. 5.2 Long- term solutions 118

5.2 Long- term solutions

5.2.1 Replacing phosphate in detergents

The implementation of phosphorus-free detergents has been successful in e.g. European countries. The possibility of this approach is worth looking into, as a matter of fact one of the present Hartbeespoort Dam remediation projects deals with this topic. Whether or not phosphorus-free detergents are used, the problem with law enforcement both at the detergent industry and sewage works still exists.

5.2.2 Stricter phosphorus standard for treated sewage water

As most recent reports have indicated that sewage works contribute the most to the phosphorus load to the dam, the implementation of a stricter phosphate standard would be an obvious strategy. The problem with this approach is however that:

• In the present political climate the existing special phosphorus standard of 1mg P/l is very poorly in the catchment area enforced. Therefore, the chances that a stricter standard will be enforced is about doubious. A standard of 0.7 mg P/l would be optimal and the ultimate goal.

• The maintenance of sewerage systems in some of the major municipalities is very poor. Even with the relative small rain storms, many main sewers overﬂow with the result that raw sewage directly enters the storm water drains.

• There still exists plenty of unsewered squatter camps which also is a potential (non- point) source of plant nutrient pollution.

Unless these problems are addressed, which are unlikely for the near future, the implementation of a stricter phosphate standard would not be a reliable and sustainable solution. Other point of attention could be to maximize wastewater reuse for irrigation and other purposes. This reduces the amount of sewage water discharged directly to the environment.

5.2.3 Pre- impoundment

One of the most concrete options on the long- term base is to build a pre- impoundment on the CR, just before it enters the dam. The principle of a pre- impoundment is mentioned 5.2 Long- term solutions 119 below. The ecohydraulic model that will be completed in the future, will be very helpful to work out the plan of the pre- impoundment more in detail. It should also be a great help to develop more and alternative long- term solutions for the dam problem.

The purpose of the pre-impoundment is to limit the buildup of phosphates in the dam which is fed from water in the Crocodile River (90% of the water supply). It will attenuate water in the river before flowing into the dam and allow sediments to settle in this small impoundment. It will also enable dredging of phosphate loaded sediments in the impoundment or allow the phosphates to be removed by means of chemical dosing. A prescribed annual minimum phosphate load for water entering the dam will be set. The focus will be on orthophosphates in suspension in the water and sediments. Phosphate loaded sediments are mainly associated with stormwater flowing in from the Crocodile River. The pre-impoundment structure will also serve to collect water in the river, which can hydraulically be diverted to a suitable location in the dam. If the first rainy season nutrient rich stormwater can be diverted to a location at the dam wall it will also help with destratifying the top warm water with colder deeper water. The pre-impoundment structure could also assist in controlling excess hyacinth growth in the river system as well as their collection and removal. A litter trap at the inlet of the Crocodile River is being planned as part of the programme to collect litter transported with stormwater from urban and informal settlements and roads. Stormwater inlets and outlets from urban areas into the rivers also need to be equipped with litter traps.

The ability of water bodies to retain large portions of the incoming phosphorus load is well known. The foundation of Research and Development has theoretically calculate the possible phosphorus load reduction that could be expected if a pre-impoundment dam with various capacities were to be constructed in the Crocodile River Arm of the Hart- beespoort Dam. With no pre-impoundment the annual average retention of phosphate in the Crocodile River Arm was about 17 - 28%. Pre-impoundment at height at full surface level (FSL) increase this to 31 - 37% and with increasing pre-impoundment dam wall height, phosphate retention increased to a maximum of 60 - 63% at FSL+10 m. This (FSL+10m) pre-impoundment dam will have a volume of 26 x 106 m3 (about 10% of the full supply volume of the Hartbeespoort Dam), a mean depth of 8.2 m and a surface area of 322 ha, based on existing morphometry of the Crocodile River Arm.

From the above it is clear that even the lowest of pre-impoundment dam walls will reduce up to 28% of the phosphorus load. This phosphorus reduction is most probably due to the settling of suspended inorganic particulate phosphate (sand and clay). The further reduc- 5.3 Conclusion 120 tion of phosphate load when the pre-impoundment wall is increased is most probably due to soluble phosphate that is converted to biomass of which a major fraction eventually settles as an organic sludge, similarly to what is presently be happening in the Hartbeespoort Dam. Unless the settled material (both the organic sludge and inorganic silt) is periodically removed, this trapped phosphorus will eventually accumulate to such a degree that especially the organic sludge will be ﬂushed into the Hartbeespoort Dam.

If this type of pre-impoundment is considered, periodical emptying and cleaning up will be essential. By capturing the phosphorus-rich particulates will not only reduce the phosphorus load to the dam, but will also prevent any phosphate-rich inorganic sediment built-up in the Hartbeespoort Dam. Consequently, pre-impoundment as a possible phosphate load reducing option should seriously be considered.

More information on the concept of a pre- impoundment can be found in annex F.

5.3 Conclusion

The reduction of the bio-available phosphorus concentration to between 30 and 50 μgP/l in the Hartbeespoort Dam has been identified as an essential prerequisite for changing the hyper-eutrophic status of the dam. From all the various proposed methods of phosphate reduction which are considered above, it is only the chemical fixing of phosphorus that will give a reliable and ensured phosphate removal to any predetermined value. The second method that will give an ensured phosphate input reduction of 55% or more (probably closer to 75%) is a pre-impoundment dam with flow diversion system as described in figure F.3. The viability of this system is presently under investigation as one of the Hartbeespoort Dam rehabilitation programs.

5.4 References

Literature

A.J. Twinch, D.C. Grobler. Pre- impoundment as a eutrophication management option: a simulation study at Hartbeespoort Dam. Water SA Vol. 12 No. 1, January 1986

B. Harding. Hartbeespoort Dam: An Action Plan. Water Wheel Magazine, 2004 Volume 3 No 6 November/December, pages 6-10. 5.4 References 121

D.C. Grobler. Assessment of the impact of eutrophication control measures on South African impoundments. Ecological Modelling, Volume 31, Issues 1-4, Scope and Limit in the Application of Ecological Models to Environmental Management 3-I 2-IV, Pages 237-247, May 1986.

O. Sawadogo, G. Basson. Analysis of Observed Reservoir Sedimentation Rates in South Africa. African Institute for Mathematical Sciences (AIMS), University of Stellenbosch, South Africa, May 2008.

P. Venter. Presentation Pre- impoundment. Information CD HBPD Integrated Biological Remediation 2009/8 - v1

W.A. Pretorius. Pre-impoundment - begroting. Report DWAF, July 2007.

W.R. Harding. Hartbeespoort Dam Remediation Project (Phase 1, Volume II). Dept. of Agriculture, Conservation, Environment and Tourism, October 2004.

Z. Cukic. Presentation Hartbeespoort Dam: Internal Load Issues. Information CD HBPD Integrated Biological Remediation 2009/8 - v1.

Chapter 6

Conclusions

The Hartbeespoort Dam is a dam with a huge economical, social and ecological value. For years, it has been degenerated, but the last ten years, active work to rehabilitate the area has been done. An eﬀective reservoir management programme for Hartbeespoort Dam is set up, based upon the recommendations of the HBPD Remediation Program. It will ensure clean water for human and environmental health. The HBPD Remediation Program could be an example to other polluted catchments in the country.

What could be concluded from chapter four, the ecological model, is that, if phosphorus is to be made the growth limiting requirement, the present average phosphorus concentration of more than 343 μg/l (2004) should be reduced by more than 80%, to bring the phosphorus concentration in the 30 to 50 μg/l range required. Nevertheless, from the diﬀerent algal growth limiting requirements available, the reduction of phosphorus concentration seems to be the most practical of all. Only by reaching this objective, the ultimate goal to change the trophic status of the dam from hypertrophic to mesotrophic, will be reached. Most attainable solution for the moment is the construction of a pre- impoundment, supplemented with some short- term actions such as chemical water treatment and sediment removal.

However the ecological modelling itself is not started yet, in the future, it will deﬁnitely contribute to the development of the existing solutions and open doors for new ideas and opportunities.

The aim of the thesis was two folded: map out the problem by means of an extensive literature study and ﬁeld visit, followed by starting the hydraulic model (basis of the ecohydraulic model). CONCLUSIONS 123

This thesis should form a broad base for further research and model development. The data collection, information and contact persons (see annex G) should simplify future work around this subject.

The now developed hydraulic model needs certainly further optimization. Especially more intense study of the longitudinal section will precise the present results. Even though it took lots of time, resulting in very few results, the STRIVE- package has a great potential for bringing in new perceptions.

Although, still lots of water will ﬂow through the Crocodile River and dam before the problem will be completely rectiﬁed, the future prospects look promising. . . ECOSTATUS OF THE CROCODILE (WEST) MARICO WMA 124

Appendix A

Ecostatus of the Crocodile (West) Marico WMA

SECTORAL WATER REQUIREMENTS 126

Appendix B

Sectoral Water Requirements LAND USE 128

Appendix C

Land Use CD- CONTENT 130

Appendix D

CD- Content

• Data-Ecological model

– Weather Data ∗ Wind ∗ Temperature ∗ Sunshine – Nuclear contamination – Water Parameters ∗ Oxigen (dissolved and saturated) ∗ Dry solid mass ∗ Nitrogen ∗ Phosphorus

∗ PO4

∗ SO4 ∗ Water temperature ∗ pH ∗ Microcystin toxins ∗ Electrical conductivity

• Data- hydraulic model

– Cross sections ∗ Dam CD- CONTENT 131

∗ Rivers and River Flow Stations – Discharge Data River Flow Stations: A2H012, A2H013, A2H014, A2H044, A2H045, A2H049, A2H050, A2H051, A2H058, A2H081, A2H082 and A2H083. – Slope data (incomplete) – Digital Elevation Maps (DEM) – Evaporation data – Rainfall data – Reservoir data

• Figures: contains all the figures used in the text, unused figures and pictures from the field trip to the HBPD.

• Information ﬁles: contains all the used information ﬁles, presentations, reports that were digital available.

• Information CD HBPD Integrated Biological Remediation: content of the oﬃcial CD issued by the Hartbeespoort Remediation Program.

• Processed data

– Floodings per section – Q-Z- relation weirs – Reservoir

• Publication: contains the Master Thesis text (pdf and LATEX- format).

• Strive model and results

– Section A – Section B – Section C – Section D MODEL OF THE DAM 132

Appendix E

Model of the dam

The complete point- model is included on the CD (Excel). date IN OUT STORAGE West East Crocodile Magalies Total Crocodile Total Rain Swartspruit Totalinflow Evaporation irrigation irrigation River River irrigation River outflow Canal Canal

A2H012 A2H013 A2H058 A2H081 A2H082 A2H083 Storage Content m3/day m³/s m³/s m³/s m³/h m3/day m³/s m³/s m³/s m³/s m³/day m3 m³ 30/11/2003 0 0,000 0,106 0,010 10022 46864,25 1,466 1,864 3,33 1,080 427888 399200 162268300 1/12/2003 0 0,000 0,104 0,011 9936 37522,4 3,332 4,080 7,412 0,997 764060 49500 162218800 2/12/2003 0 0,000 0,111 0,014 10800 149965,6 4,040 4,454 8,494 1,025 972407 244300 161974500 3/12/2003 0 0,000 0,089 0,012 8726 215219,05 4,093 4,476 8,569 1,025 1044141 452100 161522400 4/12/2003 97155,24 0,000 0,102 0,011 106918 192442,11 4,048 4,378 8,426 0,992 1006157 364500 161157900 5/12/2003 0 0,000 0,090 0,012 8813 167875,2 3,087 3,916 7,003 0,972 856915 458900 160699000 6/12/2003 18621,9 0,000 0,076 0,010 26052 115455,78 0,774 1,562 2,336 0,857 391331 122900 160576100 7/12/2003 0 0,000 0,079 0,012 7862 139664,25 1,715 2,390 4,105 0,856 568295 194000 160770100 8/12/2003 0 0,000 0,065 0,013 6739 124973,76 4,333 4,814 9,147 1,083 1008846 277100 161047200 9/12/2003 0 0,000 0,052 0,011 5443 121243,2 4,713 5,075 9,788 0,982 1051771 157300 160889900 10/12/2003 0 0,000 0,043 0,001 3802 106232,61 4,655 5,312 9,967 0,932 1047906 383200 160506700 11/12/2003 0 0,000 0,052 0,001 4579 111638,4 4,097 5,117 9,214 0,922 987389 477900 160028800 12/12/2003 0 0,000 0,055 0,001 4838 148428 3,130 4,883 8,013 0,922 920412 567500 159461300 13/12/2003 22196,88 0,000 0,047 0,000 26258 151678,68 0,944 1,608 2,552 1,061 463842 335800 159125500 14/12/2003 0 0,000 0,045 0,000 3888 166309,2 2,120 2,618 4,738 0,982 660517 66800 159058700 15/12/2003 0 0,000 0,054 0,000 4666 212506,2 5,165 5,544 10,709 0,938 1218807 111100 158947600 16/12/2003 0 0,000 0,043 0,000 3715 197123,96 5,385 5,757 11,142 0,965 1243169 764100 158183500 17/12/2003 0 0,000 0,040 0,000 3456 174137,85 5,300 6,383 11,683 1,698 1330256 949000 157234500 18/12/2003 0 0,000 0,044 0,000 3802 113073,12 4,726 7,279 12,005 2,828 1394644 891900 156342600 19/12/2003 0 0,000 0,049 0,000 4234 136227,75 3,594 5,476 9,07 1,978 1090775 538300 155804300 20/12/2003 0 0,000 0,046 0,000 3974 126758,8 0,927 2,577 3,504 0,939 510634 478400 155325900 21/12/2003 388935 0,000 0,037 0,000 392132 198990 1,763 3,213 4,976 0,916 708059 181900 155144000 22/12/2003 0 0,000 0,035 0,001 3110 168065,88 4,735 5,708 10,443 1,121 1167195 259500 154884500 23/12/2003 0 0,000 0,070 0,002 6221 162148,5 4,917 6,499 11,416 1,135 1246555 467000 154417500 24/12/2003 152828,3 0,000 0,065 0,001 158531 134848,5 2,973 4,912 7,885 1,265 925409 218300 154199200 25/12/2003 0 0,000 0,087 0,002 7690 170808,1 0,061 2,367 2,428 1,314 494117 64200 154135000 26/12/2003 0 0,000 0,109 0,004 9763 158222,24 0,066 2,364 2,43 1,354 485160 389300 154524300 27/12/2003 0 0,000 0,101 0,001 8813 176742,02 0,067 1,712 1,779 1,044 420649 526200 155050500 28/12/2003 0 0,000 0,089 0,001 7776 177282 1,407 2,710 4,117 0,998 619218 277600 155328100 29/12/2003 0 0,000 0,085 0,001 7430 244463,4 2,776 3,750 6,526 1,080 901622 23800 155351900 30/12/2003 0 0,000 0,078 0,001 6826 222507 2,459 4,088 6,547 1,149 887441 187700 155164200 31/12/2003 0 0,000 0,063 0,001 5530 225895 1,362 2,904 4,266 1,099 689431 259400 154904800 1/01/2004 0 0,000 0,086 0,001 7517 201990,88 0,061 1,511 1,572 0,954 420237 90100 154814700 2/01/2004 0 0,000 0,078 0,001 6826 162314,1 0,283 1,668 1,951 0,997 417021 36900 154851600 3/01/2004 207611,8 0,000 0,086 0,001 215129 144425,6 0,358 1,451 1,809 0,948 382630 73400 154925000 4/01/2004 0 0,000 0,094 0,001 8208 149994,28 0,965 2,158 3,123 1,108 515553 263900 155188900 5/01/2004 0 0,000 0,100 0,001 8726 139293 2,168 4,283 6,451 1,378 815719 133100 155322000 6/01/2004 0 0,000 0,112 0,001 9763 112158 2,154 4,617 6,771 1,092 791521 52800 155374800 7/01/2004 0 0,000 0,101 0,001 8813 75978 1,957 4,283 6,24 1,093 709549 82800 155292000 8/01/2004 0 0,000 0,076 0,001 6653 99393,8 1,964 3,528 5,492 1,044 664104 288800 155003200 9/01/2004 0 0,000 0,066 0,001 5789 86655,36 1,947 3,088 5,035 1,054 612745 103500 154899700 10/01/2004 261506,1 0,000 0,072 0,002 267900 75746,58 0,872 1,858 2,73 0,998 397846 161500 154738200 11/01/2004 162478,8 0,000 0,073 0,001 168872 21663,84 1,883 3,116 4,999 1,120 550345 746000 155484200 12/01/2004 0 0,000 0,066 0,000 5702 163307,7 3,195 4,976 8,171 1,164 969852 450900 155935100 13/01/2004 0 0,000 0,051 0,000 4406 172555,15 2,944 4,974 7,918 1,160 956894 125700 156060800 14/01/2004 0 0,000 0,054 0,000 4666 168922,41 2,963 4,966 7,929 1,175 955508 122900 155937900 15/01/2004 0 0,000 0,056 0,000 4838 136089,75 3,192 4,899 8,091 1,188 937795 325600 155612300 16/01/2004 0 0,000 0,048 0,000 4147 108650,4 1,982 4,161 6,143 1,157 739370 441500 155170800 17/01/2004 0 0,000 0,056 0,000 4838 102903,24 0,060 0,354 0,414 1,261 247623 74800 155096000 18/01/2004 23540,92 0,000 0,052 0,000 28034 68811,92 0,060 0,115 0,175 1,066 176034 501500 155597500 19/01/2004 719634 0,000 0,078 0,000 726373 67069,16 0,064 1,175 1,239 1,057 265444 270600 155868100 20/01/2004 385462,6 0,000 0,182 0,000 401187 67274,14 1,622 3,977 5,599 1,227 657041 757600 156625700 21/01/2004 308261,5 0,000 0,177 0,000 323554 56881,59 1,304 2,520 3,824 1,097 482056 3079700 159705400 22/01/2004 298444,8 0,000 0,209 0,000 316502 55958,4 0,088 1,514 1,602 1,046 284746 2250900 161956300 23/01/2004 75229,6 0,000 0,235 0,000 95534 39495,54 0,090 1,516 1,606 1,034 267592 1942700 163899000 24/01/2004 0 0,000 0,213 0,000 18403 104555,55 0,093 1,518 1,611 1,020 331874 3075200 166974200 25/01/2004 0 0,000 0,196 0,000 16934 96068 0,092 1,520 1,612 1,019 323386 1371700 168345900 26/01/2004 0 0,000 0,225 0,000 19440 100402,64 0,087 1,522 1,609 1,033 328671 1261000 169606900 27/01/2004 0 0,000 0,270 0,000 23328 155224 0,088 1,524 1,612 1,066 386603 781400 170388300 28/01/2004 0 0,000 0,181 0,000 15638 184779,75 0,084 1,524 1,608 1,074 416505 670900 171059200 29/01/2004 0 0,000 0,145 0,000 12528 181332,33 0,085 1,525 1,61 1,048 410984 487400 171546600 30/01/2004 0 0,000 0,122 0,000 10541 181775,94 0,086 1,526 1,612 1,058 412464 414800 171961400 31/01/2004 0 0,000 0,109 0,000 9418 181923,81 0,092 1,526 1,618 1,067 413908 161200 172122600 PRE- IMPOUNDMENT CONCEPT 134

Appendix F

Pre- impoundment concept

Background

Phosphorus removal mechanisms in a pre-impoundment dam

The pre-impoundment concept as discussed by FRD consist basically of a dam wall in the Crocodile River Arm of the Hartbeespoort Dam. The theoretical percentage of phosphorus removal depends on the wall height (and thus hydraulic retention time) - from about 20% for a wall equal to full water level (FWL) to about 65% at FWL + 10 m.

The 20% reduction at FWL would most probably be due to the physical settling of particulate phosphate (mostly inorganic). Phosphorus removal due to settling would mostly occur with storm water flow (mainly summer time). The consequence of the particulate settling is that the remaining phosphorus would mainly be in soluble form. Other than particulate phosphorus, the removal of phosphorus from solution is due to the biological uptake of this phosphate during alge (or hyacinths) growth. This is evident in the increased percentage phosphorus removal when the impoundment dam is increased in volume. Eventually, part of the algal crop dies and settles as phosphorus rich biomass which accounts for the difference of phosphorus concentration between the in- and outflow from the pre-impoundment.

The phosphorus removal mechanisms involved in pre-impoundment is thus physical settling of particulate-phosphate and the growth and settlement of algae. For the pre-impoundment dam to remain functional, the sediment (both organic and inorganic) must periodically be removed. PRE- IMPOUNDMENT CONCEPT 135

Failure of pre-impoundment dam to remove phosphorus in winter

It is mentioned above that the particulate phosphate is removed by physical settlement and the dissolved phosphorus by biomass assimilation.

The flow in the Crocodile River is not a natural flow in the sense that in a natural river the base flow (in winter) comes from springs (usually phosphorus free) and the bulk of the summer flow from stormwater runoff from mainly undisturbed soils. Contrary to this, the base flow in winter in the Crocodile River is the compilation of effluents of more than eight sewage works, discharging on average > 464 Million l/day in 2004.

Other than stormwater, sewage eﬄuents in general contain virtually no inorganic particulate solids so that if it contains phosphate, the phosphate would be wholly in the soluble ortho-phosphate form. This means that during the dry (winter) season, all the phosphate reaching the pre-impoundment (or the Hartbeespoort Dam) would be in the soluble form. As soluble phosphate is mostly removed by biological intervention, and biological growth is very temperature (and light) dependent, only a small fraction of this phosphate will be removed by the pre-impoundment dam during the winter season.

From this it can be concluded that a pre-impoundment dam in the Crocodile River Arm to the Hartbeespoort Dam will fail six months in a year to remove any signiﬁcant amount of phosphorus.

Pre-impoundment - Alternative approach

Water budget for Hartbeespoort Dam

The long-term water budget for the Hartbeespoort Dam is given in table F.1.

From table F.1 it can be seen that from river inﬂow of 224 x 106 m3 per annum, 105.7 x 106 m3 (or 47%) was regulated discharges. River water through the sluice gates was 101.9 - 9.5 = 92.4 x 106 m3 (or 41.3%). Thus, in 1978 more water was discharged as controlled abstractions than water that left the dam via the sluices.

Since 1987 the annual inﬂow has increased due to more treated sewage discharged into the Crocodile River catchment. Although the ﬂow contributed by sewage in 1978 is not mentioned in the FRD report, the treated sewage in 2004 was for example about 170.2 x 106 PRE- IMPOUNDMENT CONCEPT 136

Inflows (x 106 m 3) River inflow 224 Precipitation 9.5 TOTAL in 233.5 Outflows (x 106 m 3) Sluices 101.9 Abstractions: Irrigation 82.3 Compensation water 16.9 Potable 6.5 Seepage 1.3 Total controlled abstractions 105.7 Evaporation 18.9 TOTAL out 227.8

Table F.1: Long- term water budget for Hartbeespoort Dam (1964-1978) m3/a. This treated sewage ﬂow is more than 60% more than the total controlled abstraction during 1978. Where the controlled abstraction of water from the Hartbeespoort Dam in 1978 was mainly for irrigation and compensation water, this situation is to be changed drastically in the near future. In this respect it is envisage that the Hartbeespoort Dam will have to supply water for a new power station (ESKOM) and a fuel from coal plant (SASOL) in the foreseeable future.

For these abstractions to be sustainable and reliable, the Hartbeespoort Dam will have to be manage in such a way that the maximum annual volume of storm water is of its inflow is made available for use. This means that the water level will be mainly always below the TWL so that very little if any water will leave the dam as overflow during the rainy season. Under such conditions the Hartbeespoort Dam can be considered as very large flow equalisation basin.

The concept of ﬂow equalisation

Flow equalisation simply is the damming of a variable inflow rate to achieve a constant or nearly constant outflow rate. For equalising a variable inflow an equalising basin of specific minimum volume is required. This minimum equalisation volume required, is a function of the time variations in the inflow rate measured over a period of time - the greater the PRE- IMPOUNDMENT CONCEPT 137 time variation of the inflow, the larger the minimum equalisation volume required and vice versa.

Equalisation can be operated as an in-line or an off-line system. In the in-line system, all the flow goes through the equalisation basin. In the off-line system the required constant outflow is taken directly from the variable inflow. If the variable inflow rate is more than the constant outflow, water is diverted to the equalisation basin, and if the constant outflow rate is higher than the inflow rate, the difference of flow is taken from the equalisation basin. The minimum volumes of the equalisation basins mentioned above are the same. The two systems are schematically shown in figure

The minimum size of an equalization basin is usually expressed as a fraction of the total ﬂow over a cyclic period - for wastewater it is usually a 24 hour period and for a impoundment, a year. In wastewater treatment the fractional volume is typically between 10 and 20%.

The volume of an equalization basin varies continuously accordingly to the relative inflow and outflow rates at any moment in time - when the outflow rate is lower than the inflow rate, the equalization basin is in a fill mode; when the outflow rate is higher than the inflow rate the equalization basin is in a discharge mode and there is no change in equalization volume when the outflow rate is equal to the inflow rate.

Applying the ﬂow equalization concept to Hartbeespoort Dam

Pre-impoundment without ﬂow diversion

With the planned new power station and a new Sasol factory which are to receive their water from Hartbeespoort Dam, the total water demand from the dam will increased to such an extent that very little or no water will leave the dam over the stormwater weir. This means that the Hartbeespoort Dam will function as a sort of an in-line equalization tank but with a large ”dead” volume fraction (dead volume is the volume not required for ﬂow equalization).

As the ”dead” volume fraction (with regard to flow equalization) of the dam will be the major part of the dam, the phosphate rich winter overflow of a usual pre-impoundment dam will have the same effect on eutrophication as what the present situation is. Figure PRE- IMPOUNDMENT CONCEPT 138

Figure F.1: In- and oﬀ-line ﬂow equalization

F.2 shows the flow distribution from a usual pre-impoundment dam. The outflow from the pre-impoundment follows the total length of the dam before reaching the outflow.

Figure F.2: Usual pre- impoundment

Pre-impoundment with ﬂow diversion

A modification of the usual pre-impoundment is recommended. In this modification the pre-impoundment dam is constructed to act only as a particulate phosphate trap (which PRE- IMPOUNDMENT CONCEPT 139 is important during the rainy season). The soluble phosphate rich water is diverted to the Hartbeespoort Dam wall through submerged pipes. At the Hartbeespoort Dam wall the bulk of this ”by-passed” flow will accumulate more or less in the vicinity of the dam wall where this water will be first to leave the dam as controlled outflow. Figure F.3 schematically shows this concept.

Figure F.3: Pre-impoundment with ﬂow diversion

As the Hartbeespoort Dam will act similarly to an equalization basin, the water level of the dam will, change continuously. During the rainy (summer) season the dam will gradually fill so that it reach its maximum (usually overflow) level at the end of this season. During the following (autumn-winter) season the water level will gradually drop until this level is a minimum at the end of the dry season. The actual level fluctuations will depend on the volume of inflow and the corresponding volume extracted during that particular year.

Probable phosphorus load reduction with a pre-impoundment with ﬂow diversion

The following assumptions are made:

1. Most of the soluble phosphate in the Crocodile River originates from treated sewage

2. The Total phosphorus in storm water is the sum of insoluble particulate (sediment) phosphate and soluble phosphate. 20% of the phosphorus in stormwater is in the insoluble particulate form

3. The soluble phosphate load in stormwater is all from treated sewage origin PRE- IMPOUNDMENT CONCEPT 140

4. All particulate phosphate in the Crocodile River is removed by settling in the Pre- impoundment dam

The only uncertainty on the probable phosphorus removal by this system is the fraction of soluble phosphate load that is discharged into the Hartbeespoort Dam during stormwater flow (i.e. when the Hartbeespoort Dam is in a filling mode). The percentage of phosphorus removal for increasing soluble fraction removal during filling is shown in table F.2.

Percent of soluble P load in outﬂow Percentage of inﬂow P load removed with con- during rainy season trolled discharge 0 55 10 59 20 64 30 68 40 73 50 77 60 83

Table F.2: Percent P load reduction for diﬀerent fractions soluble P in outﬂow during the rainy season

Table F.2 shows that a minimum of 55% and a probable maximum of up to 83% of the phosphorus load in the Crocodile River can be prevented from entering the Hartbeespoort Dam by the proposed Pre-impoundment with ﬂow diversion system.

Advantages of pre-impoundment with ﬂow diversion

1. Particulate phosphate and debris is removed in the Pre-impoundment dam where it can be removed - thus no more debris and phosphate rich sediment into the Hart- beespoort Dam.

2. No soluble phosphate input into the Hartbeespoort Dam during the dry (winter) season - during this season there is a net outﬂow from the dam and as the diverted water is discharged at the dam wall, all this water (plus the balance of the demand from dam water) leaves the dam as controlled outﬂow.

3. During filling (rainy season), excess (difference between in- and outflow rates) water is discharged near the dam wall. Here the surface area volume ratio of the dam is PRE- IMPOUNDMENT CONCEPT 141

a minimum - light energy becomes a growth limiting factor which will reduce the growth potential of blue-green alge.

4. The quality of the out ﬂowing water will in general be better than what it is at present - will contain less organic (blue-green) algae pollution than at present.

5. Only maintenance require for this system is the periodic removal of debris and inorganic sediment from the Pre-impoundment Dam.

Source: W.A. Pretorius. Pre-impoundment - begroting. Report DWAF, July 2007. REPORT UNESCO 142

Appendix G

Report Unesco PreparationMasterThesis: “Ecohydraulicmodellingofthe HartbeespoortdamandCrocodileRiver” Student:MichaelDeClercq 6Septemberto11October2009 Venue:Hartbeespoort–SouthAfrica

TableofContents 1. Introduction...... 3 1.1. Outlineoftheproblem...... 3 1.2. Objectiveofthethesis...... 3 1.3. ObjectiveofthetriptoHartbeespoortSouthAfrica...... 3 2. Overviewofthemeetings...... 5 2.1. Description...... 5 2.2. Contactdetailslist...... 7 3. Programofactivities...... 9 4. Overviewofthetotalcosts...... 14

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1. Introduction 1.1.Outlineoftheproblem TheHartbeespoortdamislyingontheCrocodileriverintheNorthWestProvinceofSouthAfrica. Itsuffersaveryseriouseutrophicationproblem. Wikipedia(source:http://en.wikipedia.org/wiki/Eutrophication): “Eutrophicationisfrequentlyaresultofnutrientpollution,suchasthereleaseofsewageeffluent, urban storm water runoff, and runoff carrying excess fertilizers into natural waters. Eutrophication generally promotes excessive plant growth and decay, favors certain weedy speciesoverothers,andmaycauseaseverereductioninwaterquality.Inaquaticenvironments, enhanced growth of choking aquatic vegetation or phytoplankton (e.g. algal blooms) disrupts normalfunctioningoftheecosystem,causingavarietyofproblemssuchasalackofoxygenin the water, needed for fish and shellfish to survive. The water then becomes cloudy, colored a shadeofgreen–blue.Humansocietyisimpactedaswell:eutrophicationdecreasestheresource value of rivers, lakes, and estuaries such that recreation, fishing, and irrigation are hindered. Healthrelated problems can occur where eutrophic conditions interfere with drinking water treatmentandirrigationwater.” The Crocodile River leads down the water from the upwards situated residential area of Johannesburg and Pretoria, where to many contaminations enter the river. This results in the fact that the water of the Hartbeespoortdam is so much loaded with contaminations (phosphorusandnitrogen)thatisnotusableanymorefortheirrigationofthedownwardlying agricultural land. A model of the dam should be worked out in order to look for possible scenariostosolvetheproblemofeutroficationasaccurateaspossible.Forthispurpose,infirst instanceareliablewaterdischargemodelisneeded.

1.2.Objectiveofthethesis Purposeofthemodelistosimulatevariousscenariosoveralongerperiodwiththeaimtowork outhowtheeutroficationprobleminthedamcanbesolvedinthebestway.Itshouldhelpto predictthefuturedevelopments,tracethecriticalpointsandassignpriorities.Itshouldbenefit forthecurrentresearchprojectsandanaidfordevelopingfutureplans. Inthefirstpart,purposeistomakeahydraulicmodeloftheHartbeespoortdamanditsmain supplyingriver,theCrocodileRiver.Inthesecondpartofthemodelling,anecologicalmodelis made(algaemodel,pollutionspreadingmodel)andtriedtobelinkedwiththehydraulicmodel.

1.3.ObjectiveofthetriptoHartbeespoortSouthAfrica AstudentisintendedtoinvestigatethewaterqualityproblemsoftheHartbeespoortdamand CrocodileRiver.Supportedbyalocalsupervisorandbymeetingseveralinvolvedstakeholders (scientists, engineers, management people), he is expected to make a clear outline about the ecologicalandhumanimpactoftheeutrophicationprobleminthedam.Atthesametime,data (topographical,hydraulical,biological,chemicalandhydrological)canbecollected. Usingthecollecteddatasets,amathematicalmodeloftheriverbasinanddamreservoirwillbe built.Tobuildthemodel,thestudentcanusetheavailablesoftwarethatisdevelopedbythe

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LaboratoryofHydraulics(UniversityofGhent).Themodelthathastobebuiltismeanttobea baseforfurtherdevelopmentofsolutions. Tobuildanecohydraulicmodel,thedataneededforthemodelthatshouldbecollectedconsists offourmajorparts.Thesefourdifferentcategoriesare: Topography:allgeometricaldatasuchascrosssections,longitudinalprofiles,altitudes etc. Hydrology: all meteorological information such as rainfall and evaporation rates, dischargeseries,waterconsumptionanddemandetc. Hydraulics:constructionandmanagementcharacteristics Biologicalandchemicaldata:allparametersinfluencingbiologicalgrowth

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2. Overviewofthemeetings 2.1.Description DuringthestayinSouthAfrica,Imet alotofpeoplewhowereprofessionallyinvolvedinthe issue of the Hartbeespoortdam eutrophication problem. What follows is an overview of the activitiesandmeetingsIhadduringmyfiveweekvisit. The first week of the stay, I focused on gathering general knowledge about the dam and its problems.Thefirsttwodays,IhadappointmentswithMr.FrikkieBotha.Heisaretiredchemical engineer,whoismakingamasterthesisonthemanagementofthedamrehabilitationprogram. Hegavemealotofliterature,sotwodaysofliteraturestudywerenecessary.Thefirstdayswere alsousedtoexplorethedamreservoir,thedamwallandthesurroundingarea.Togetherwith Mr.Botha,themeetingsforthesecondweekwereplanned. Thesecondweek,IhadsomeappointmentswithlocalpeopleinvolvedintheHartbeespoortdam issue. Dr.ZoranCukicisaconsultantandisspecializedinriveranddamsedimentation.Asalotofthe nutrientsarefixedtosedimentation,thisisanimportantpartoftheprobleminthedam. Prof.BraamPieterseisprofessorinbotanyattheNorthWestUniversity.Hespecializedinthe ecophysiologyoffreshwateralgae,anddidresearchprojectsonHartbeespoortandRoodeplaat Dams.Thebulkofhisresearchactivitieswere,however,focusedontheVaalRiversystem,where hedevelopedanunderstandingofconditionsinfluencingthegrowthofplanktonicalgae,aswell asconditionsresponsibleforthedevelopmentofalgalblooms. WilliePotgieterisanenvironmentalengineer,workingasaconsultant.Heisresponsibleforthe Fundraising,Engineering,SocioEconomicModelling&DecisionMakingofthe“Harties,metsia me”–remediationprogram. PetrusVenteristheDeputyRegionalDirectoroftheCrocodile–WestMaricoarea,whichthe Hartbeespoortdammakespartof.Heisthemostknowledgeablepersononthedamissue. The17thofSeptemberIwent,togetherwithtwoFETWaterstudents(BertSchepensandJan Putteman – “Hydraulic modelling of the Lower Orange”) and Mrs. Annette Wentzel, to the annualmeetingoftheWaterResearchCommissioninMidrand(Pretoria).TheWRCpresentedits newonlineknowledgedatabase.Thedatabasecontainsallthedocuments,studiesandreports published at the WRC. The meeting was an excellent opportunity to meet all kinds of people (professors, scientists, consultants, government officials,) involved in the water and environmentalissuesofSouthAfrica. ThedatabankwasoneofthemostimportantsourcesofinformationformyMasterthesis.

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Figure1:Presentationofthenewdatabase(photobyJanPutteman)

Thenextday,IwenttotheWRCofficetoobtainsomeelderreportsoftheWRC,astheyweren’t availableonthenewinternetdatabase. Mondaythe21stofSeptember,inthemorningwe(me+theothertwoFETWaterstudents) visitedthelibraryoftheUniversityofPretoriatogetsomemorearticlesandpublicationsabout Hartbeespoortdam,modellingandeutrophicationproblems.Lateronthatdaywewenttothe nationalofficeofDWAFtotalkwithpeopleofthefloodsection(Mr.BrunkDuplessis).Theyalso providedflowdataandwaterleveldata.WealsometMr.EddievanWyk,whoisagroundwater specialistandMrs.NicoleneFourie,whohelpeduswithGISdata(=GeographicalInformation System) data of the Crocodile River basin and the dam reservoir (cross sections, longitudinal profiles,…). Therestofthethirdweek,Ispendonliteraturestudy,internetresearchandplanningtherestof mytrip.Alsothefirstpreparationsweremadeforacross–SouthAfricanroadtriptoCapeTown. The fourth week, I picked up a rental car so I would be able to drive to the meetings myself (beforeIhadtogowithotherpeopleorborrowthecarofMrs.AnnetteWentzel.OnMonday afternoonImetupwithMrs.NicoleneFourie,whohadpreparedtheGISdataforus. In the afternoon I visited Pretoria city centre and the Rietvlei Nature Reserve. In this nature reserve, the Rietvlei dam is situated. This dam suffers the same problem as the Hartbeespoortdam, bud in a much smaller scale. They developed some small measures to opposethealgaegrowthandeutrophicationproblem.Itisoneofthecasestudiesthatareuseful formyMasterThesis. OnTuesdaytherewasalargescalewatersamplingonthedamreservoir.Menco,alocalresearch company,ismakinganalgaemodelofthedam.Purposeofthesamplingistotakethesamples on the same moment a satellite passes by. Afterwards the results of the water quality of the samples coming from all over the dam is compared with the satellite picture. In that way, scientistwillbeabletolinkatintofgreenonthepicturetoaquantityandqualityofthealgaein thereservoir. Helpingwiththissamplingwasagreatopportunitytoseethewaterandtheriparianzonevery closely.Itgavemeabetterviewonthedamecosystem.

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On Wednesday I had an appointment with Mr. Hannes Pretorius. He is a local engineer responsible for the operation of the Hartbeespoortdam. He gave me general info on thedam wall,waterlevelcontrolandhistoryofthedam. OnThursdaythefirstofOctoberIvisitedthe“CradleofHumankind”.Thissiteissituatednorth westofPretoriaandisUNESCOWorldHeritage.Thefirstcompleteancienthumanskeletonwas foundinthisarea. NextdayIdidsomesightseeingbycar.PurposewastotakeasmanypicturesoftheCrocodile Riveraspossible.Thiswasnotaneasyassignmentatall.Mostoftheriparianzonewasprivate propertyorwashiddeninanareawithoutroads.Idecidedsailingtheriver wouldbeamore successfuloperation. OnSaturdayIstartedmyroadtriptoCapeTown.Purposeofthistripwashavingamoregeneral viewonthecountryanditslargedifferences.IleftintheverydryGautengProvinceandendedin themorewetcoastalareaofCapeTown.DuringthetripIrealizedtheproblemsofdroughtthe country suffers and the importance of the dams to provide water to people and agriculture duringthewholeyear.TheendofthedayIreachedGariepDam,thelargestdaminSouthAfrica. OnSundaythe4thofOctober,IvisitedtheGariepDamandcontinuedmytripthroughtheKaroo desertuntilBeaufortWest.The5th,6thand7thIvisitedCapeTownandthesurroundingarea.On WednesdayeveningIflewbacktoPretoria(Lanseria). On Thursday I was going to meet Mr. Hannes Pretorius again for a visit tothe Hartbeespoort damwallitself.Unfortunatelyhecancelledthismeeting.NextdayIhadameetingwithDr.Carin vanGinkel.ShedidaPhDongrowthofthe“cyanobacteria”,themostimportanttypeofalgaein the Hartbeespoort dam. She provided me general information on algae growth and types of algaegrowingintheSouthAfricandams.ShebroughtmeincontactwithMrs.ErasmusMarica (DWAF)whoprovidedmethealgaedata. Saturday,thepenultimatedayIrentedaboatsoIcouldseesomeinterestingplacesonthedam reservoir(rivermouths,birdbreedingplaces,damwall,…).Itgavemeaclearviewonthedam ecosystem.WealsotriedtosailontotheCrocodileRiver.Unfortunatelythewaterwasn’tdeep enoughsowecouldn’tgothatfar. Sundaywasthelastday,soitwastimetopackmysuitcasesandhavingthelastmealtogether withmylocalsupervisors,JohanandAnnetteWentzel.

2.2.Contactdetailslist (seenextpage)

PreparationMasterthesisHartbeespoortdam ProvidedData contactperson Organization email Weatherdata CharlotteMcBride SouthAfricanWeatherservice [email protected] Digitalelevationmaps NicoleneFourie DWAFdivisionGIS [email protected] FlowDATA SibanyoniFrancinah DWAFdivisionflowdatamanagement [email protected] BrunkDuPlessis DWAFdivisionflowdatamanagement Dataonwaterquality ErasmusMarica DWAF [email protected] Dataonzooplankton ErasmusMarica DWAF [email protected] Dataondamwalldetails HannesPretorius LocalDWAF [email protected] Dataongroundwater Eddievanwijk GroundwaterdivisionDWAF PublicationsWRC WRC Publications UniversityofPretoria InformationonalgaeinHartbeespoortdam KarinvanGinkel Independent [email protected] Biologicaldataandwaterqualitydata MornédeJager Menco [email protected] JohanMaré [email protected] GeneralInformationHartbeespoortdam eutrophicationproblem Prof.BraamPieterse NorthWestUniversity [email protected] Dr.ZoranCukic Metago [email protected] GeneralInformationHartbeespoortdam+ FETWater supervisionofthestayinSouthAfrica AnnetteWentzel coordinator [email protected] FrikkieBotha independent [email protected]