Monitoring and Modelling of Water Flow and Quality at the Hoffselva DEMO Site (Oslo)
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Monitoring and modelling of water flow and quality at the Hoffselva DEMO site (Oslo) Mads Arntsen Civil and Environmental Engineering (2 year) Submission date: June 2016 Supervisor: Tone Merete Muthanna, IVM Co-supervisor: Peggy Zinke, IVM Norwegian University of Science and Technology Department of Hydraulic and Environmental Engineering Abstract Hoffselva is one of the main rivers in Oslo, flowing from Holmenkollen in the north and down to the fjord by Bestumkilen. Due to low capacity of the pipes in the sewer network, the river is experiencing a rapid frequency of emissions to the river through combined sewer overflows (CSOs). The water quality is poor due to the CSO emissions and other emissions. The municipality of Oslo wants to reach the target of good chemical and ecological state within 2021, set by the national water regulation. The on-going EU-project DESSIN (Demonstrate ecosystem services enabling innovation in the water sector) aims to improve the water quality by using innovative local treatment solutions that enable cost efficient, sustainable mitigation of overloaded sewer systems and thereby increasing the value of eco system services. The aim of this master thesis is to contribute to the project by setting up, calibrating and applying a 1D hydrodynamic and water quality model for Hoffselva, and to investigate and discuss the potential influence of improved water quality from CSO spills on selected water quality indicators in Hoffselva. To fulfill the objectives, the author has used modeling programs like MIKE URBAN, HEC-RAS and ArcGIS: ArcMap. An existing model in MIKE URBAN has been used to model the activity of combined sewer overflow events during a selected 9-days rain period from the Autumn in 2014. An one-dimensional steady and unsteady simulation model were built in HEC-RAS to simulate the hydrodynamics of the river, and to make a basis for the water quality simulations in the water quality module in HEC-RAS. The CSO activity modeling for the selected event in MIKE URBAN showed three active CSO (out of 24) in the southern, urban part of the catchment. The results are consistent when compared to the CSO frequency history. Several problems with numerical instability occurred in the unsteady simulations. The unsteady model had to be reduced and simplified to successfully run an unsteady simulation for the lower part of the river. The first unsteady simulation in HEC-RAS gave higher discharge values in the hydrographs than what were observed. After some calibration, the simulated values made a good visual fit with the observed values. The water quality analysis had to use the hydraulic plan from the steady flow simulation due to an unknown error massage with the unsteady flow data. Different scenarios were made to simulate the water quality under different river conditions for a selected CSO event. The results were consistent with previous reports about poor water quality in the river. The local treatment solution was able to reduce the concentration peaks, but due to the background concentrations in the river, the water quality remained poor for the river Hoffselva in the investigated scenarios. Based on the findings, future work should measure the water quality during different rain events / scenarios, and compare the observed results with the simulated results from the model. Future work on the models should focus on using more detailed measurements as input to the models, as appropriate information about the river discharges is essential. It is suggested to make an unsteady calibrated model for the whole river network in order to have the opportunity to simulate multiple active CSOs at the same time. I II Sammendrag Hoffselva er et av hovedvassdragene i Oslo. Hoffselva renner fra Holmenkollen i nord, og sørover til utløpet ved Bestumkilen i Indre Oslofjord. Som følge av lav kapasitet på avløpsnettet, opplever elva hyppige utslipp fra overløp langs elva. Vannkvaliteten er dårlig som følge av alle overløp-utslippene og andre kilder til utslipp i elva. Oslo kommune har et ønske om å oppnå målet i Vannforskriften om god kjemisk og økologisk tilstand i alle vassdragene innen år 2021. Det pågående EU- prosjektet DESSIN (Demonstrate ecosystem services enabling innovation in the water sector) arbeider med å forbedre vannkvalitet ved bruk av innovative og lokale behandlingløsninger som muliggjør kosteffektivt, og bærekraftig klimatiltak for overbelastede avløpssystemer og dermed øke verdien til økosystemtjenester. Formålet med masteroppgaven er å bidra til prosjektet ved å sette opp, kalibrere og benytte en 1D hydrodynamisk modell og en vannkvalitetsmodell for Hoffselva, og undersøke og diskutere potensiell påvirkning av forbedret vannkvalitet for overløp-hendelser ved å se på utvalgte vannkvalitetsindikatorer i Hoffselva. Til å utføre oppgavene, har forfatteren benyttet modelleringsprogrammer som MIKE URBAN, HEC-RAS og ArcGIS: ArcMap. En eksisterende MIKE URBAN modell fra 2011 har blitt brukt til å modellere overløpsaktivitet i løpet av en 9-dagers periode fra høsten 2014. En en-dimensjonal stasjonær og ikke-stasjonær simuleringsmodell ble laget i HEC-RAS for å simulere hydrodynamikken i elva, og for å bli brukt som grunnlag til vannkvalitetsimuleringen i vannkvalitetsmodulen til HEC-RAS. Simuleringen av overløphendelser i MIKE URBAN viste at tre (av 24) overløp, i den urbane delen sør i avløpsnettet, var aktive for simuleringsperioden. Resultatene stemmer godt overens med tidligere overløphistorikk fra perioden før 2011. Den første ikke-stasjonære simuleringen gav høyere vannføring i elva enn hva som ble observert. Etter litt kalibrering, oppnådde modellen en god visuell passform mellom simulert og observert vannføring. Vannkvalitetsanalysen måtte benytte de hydrauliske resultatene fra den stasjonære strømning simuleringen, som følge av en error i programmet som oppstod ved bruk av den ikke- stasjonære strømning simuleringen. Forskjellige scenarioer ble laget for å simulere vannkvaliteten under forskjellige forhold i elva for overløphendelsen. Resultatene samsvarer med hva andre rapporter har kommet frem til: dårlig vannkvalitet i Hoffselva. Den lokale behandlingen ved overløpet klarte å redusere toppene av forurensningen, men pga. bakgrunnskonsentrasjonene i elva, forble vannkvaliteten tilnærmet uendret. Basert på erfaringer underveis, bør fremtidig arbeid inkludere vannkvalitetsmålinger og vannføringsmålinger under forskjellige regnhendelser, og benytte måleresultatene til å sammenligne og kalibrere modellen. Fremtidig arbeid med modellene bør fokusere på å benytte detaljerte målinger da informasjon om vannføringer er helt essensielt for å få til en god modell. Det anbefales å etablere en ikke-stasjonær hydrodynamisk modell for hele elvenettet for å kunne simulere flere overløp-utslipp samtidig og for å få variasjon i vannføring over tid. III IV Preface This master thesis is submitted in the Department of Hydraulic and Environmental Engineering at the Norwegian University of Science and Technology (NTNU). The master thesis is a part of a 2-years master degree within the study programme Civil and Environmental Engineering. It accounts for 30 ECTS, and it was conducted during the spring 2016. It contains the work of the author under supervision of Postdoctoral Fellow Peggy Zinke and secondary supervisor Associate Professor Tone Merete Muthanna from NTNU. It has been a lot of work and many challenges along the way, but that is also one of the main reasons why I chose this topic. I was triggered by the big potential to explore and learn from the project, as it is a part of something bigger. The use of modeling programs is something I have an interest for, and I have learned a lot from the work in this master thesis. One of my criteria’s was that necessary supervision should be in place in order to conduct the different tasks along the way. I have met a lot of interesting and helpful people along the way which have given me extra encouragement and energy to keep working. I have experienced how much this important topic means to the different participants in the project, and how the different interests all relate to the same topic. Among all the people I have encountered and met along the way, I would especially like to thank some of you. I would like to thank: - Oslo VAV for their kindness and willingness to share and provide information, and to accommodate a one week stay at their office. Especially thanks to Samatar Abdi Mahammud for supervision on the MIKE URBAN modeling. - Ashenafi Seifu Gragne for the help with HEC-RAS, and for his work with the calibration of discharges, and all the good talks and discussions along the way. - Samuel Vingerhagen from SWECO for the supervision with the HEC-RAS model - Inrigo Water AS, represented by Cheng Sun and Viggo Bjerkelund, for providing information about their treatment solution. - Herman Helness and SINTEF for providing information and support during the master thesis period. Lastly I would like to thank my supervisor, Peggy Zinke, for giving excellent guidance and having faith in me. She has been an important support with encouraging attitude and always some thoughts on how we can make things work out, for which I am very thankful. V VI List of content Abstract ....................................................................................................................................... I Sammendrag ............................................................................................................................. III Preface ......................................................................................................................................