SITUATION ANALYSIS OF PROBLEMS FOR WATER QUALITY MANAGEMENT IN THE LOWER ORANGE RIVER REGION WITH SPECIAL REFERENCE TO THE CONTRIBUTION OF THE FOOTHILLS TO SALINIZATION. by T. Volschenk1), M.V. Fey2) & H.L. Zietsman3) 1) Soil Science Division, ARC Infruitec-Nietvoorbij, Stellenbosch 7599 2) Department of Soil Science, University of Stellenbosch, Stellenbosch 7602 3) Department of Geography and Environmental studies, University of Stellenbosch, Stellenbosch 7602 Final report to the Water Research Commission and Northern Cape Department of Agriculture and Land Reform JULY 2005 ISBN No.: 1-77005-378-6 Report No.: 1358/1/05 TABLE OF CONTENTS EXECUTIVE SUMMARY iv ACKNOWLEDGEMENTS xiii LIST OF TABLES xv LIST OF FIGURES xviii 1 INTRODUCTION 1 1.1 Objectives 6 1.2 Structure of the report 6 2 LITERATURE 7 3 WATER QUALITY OF THE LOWER ORANGE RIVER 11 3.1 Introduction 11 3.2 Data collection, retrieval and processing 11 3.3 Results and discussion 13 3.3.1 Status of water quality monitoring sites 13 3.3.2 General classification of river water quality 14 3.3.3 Trends in river water quality. 20 3.3.4 Trends in drainage water quality 32 3.3.5 Salt retention in the Boegoeberg to Onseepkans river reach 35 3.4 Conclusions 38 4 SALT GENERATION POTENTIAL OF SOILS IN THREE CONTRASTING AREAS UNDER IRRIGATION 40 4.1 Introduction 40 4.2 Materials and methods 41 4.3 Results and discussion 43 4.3.1 Field soil properties and exchangeable cation content 43 4.3.2 Laboratory weathering by equilibration 48 4.3.3 Soluble salt composition 54 4.3.4 Laboratory weathering by leaching 55 4.3.5 Effect of gypsum and manure applications on soil salinity 57 4.3.6 Composition of drainage water from selected catchments 57 4.4 Conclusions 60 5 IDENTIFICATION AND CLASSIFICATION OF CULTIVATED AREAS UTILIZING SATELLITE IMAGERY 62 5.1 Unsupervised image classification 62 5.2 Vegetation Indices 64 5.3 Higher resolution satellite imagery 69 6 IDENTIFICATION, CLASSIFICATION AND VERIFICATION OF POTENTIALLY SALINIZED AREAS UTILIZING AERIAL SURVEY IMAGERY 71 6.1 Spatial sampling strategy 73 6.2 Orthorectification of imagery 75 6.3 Object-oriented image classification 77 6.4 Verification of potentially salinized areas 86 6.5 Conclusions 89 7 WATER QUALITY AND SOIL SALINITY MANAGEMENT 91 7.1 Situation assessment 92 7.1.1 Management practices 92 7.1.2 Institutional structure and catchment management 93 7.1.3 Water quality management strategy 93 7.2 Options for water quality and soil salinity control 95 7.2.1 Minimization of irrigation return flow 96 7.2.2 Drainage water management 101 7.3 Guidelines for water quality and soil salinity management specific for the Lower Orange River Water Management Area 103 7.4 Conclusions 103 8 CONCLUSIONS 107 9 REFERENCES 111 10 ARCHIVING OF DATA 119 11 LIST OF PUBLICATIONS AND OTHER TECHNOLOGY TRANSFER ACTIONS 120 APPENDIX A Drainage water quality data 121 APPENDIX B Soil analysis data 124 APPENDIX C The potential effect of salinity on grapevine production 144 EXECUTIVE SUMMARY Introduction Sustainable and efficient use of water is implicit in the 1998 National Water Act of South Africa. The most feasible manner in which to achieve this is by integrated water resource management through licensing water and allowing larger user participation in management of the water resource. Water resource management is to be performed by two types of institutions, namely a Catchment Management Agency (CMA) and a Water User Association (WUA). The function of the CMA is integrated catchment management according to a catchment management strategy (CMS). One CMA is foreseen for each of the 19 water management areas (WMAs) in South Africa. The WUA will form at a more local level than the CMA to coordinate different users in the day-to-day management of an irrigation scheme, a river or a catchment. Water quality is related to water quantity and should form a part of integrated water resource management. The national water quality management framework policy is therefore aligned with the National Water Act. Integrated water quality management comprises several facets, but water quality planning ultimately determines its principles of action. Catchment assessment studies continually serve to provide information regarding the physical and socio-economic cause-and-effect relationships underlying the principal water related problems in the WMA and its sub-catchments. Such studies enable the water quality manager to formulate a catchment water quality management strategy. The strategic management of water quality at the WMA and sub-catchment level is collectively governed through 19 CMSs. This is to facilitate alignment between WMAs, or sub-catchments within a WMA, where water quality impacts on downstream-users. Such joint management of catchments is considered a necessity in the case of the Orange River which is the largest and most strategic water resource in South Africa. One of the most comprehensive river assessment studies performed in South Africa namely, the Orange River Replanning Study, indicated potential for water quality related problems in the Lower Orange WMA, particularly in the river reach between Boegoeberg and Onseepkans. The lower Orange WMA is located in an arid area with limited rainfall that is characterized by high evaporation losses. The tributary inflows in the area are intermittent, and only contribute to river flow during periods of unusually high precipitation in the Lower Orange River basin. The salt contribution of these rivers and natural streamlets to the Orange River during such events is unknown. The bulk of the surface water of the Lower Orange WMA is found in the main stem of the Orange River and almost all of its surface water originates from Lesotho, the Vaal WMAs and the Upper Orange WMA. Both the water flow and water quality in the Orange River have been severely affected by extensive upstream developments due to transfer of good quality water out of the Orange River in Lesotho and the Upper Orange WMA, high salinity irrigation return flows along the Orange River and inflow of poor quality water from the Vaal River. Furthermore, a considerable amount of salt (ca. 3 million tons) originating from irrigation water has been withheld from the Vaal River, and subsequently the Orange River, by the Vaalharts irrigation scheme since its inception in 1935. It is feared that this salt may cause serious problems for irrigation farmers downstream if the storage capacity of its ultimate sink is exceeded, resulting in highly saline groundwater flows. IV In the Lower Orange WMA, irrigation is the dominant water use and comprises 94% of the total water requirement compared to 3%, 2% and 1% thereof, respectively, for urban, rural and mining purposes. Nearly all irrigation developments are dependent on water from the river. More than 35 000 ha of land are cultivated between Boegoeberg and Onseepkans, with grapes (60%) and cotton (ca. 20%) constituting the main crops. Other crops include lucerne (8.2%), wheat (7.9%) and maize (3.5%). Most of the irrigation water is applied to high value orchard type crops of which yield and quality may be negatively affected by water deficits or excessive salinity. The irrigation water is therefore needed with a relatively high assurance of supply and should be of acceptable quality. Irrigation return flow constitutes an important part of the overall water balance of the Orange River and may be as high as 30% of water applied to the land. In comparison, urban and industrial return flows are minimal. Water quality of the return flow is generally poor. The magnitude and salinity of irrigation return flow to the river and canal systems, the extent and salt load of irrigation-induced recharge of groundwater, as well as the possible inflow of groundwater to surface water along the river are important factors dictating river salinization, especially in arid areas. Such information is still unknown for the Lower Orange WMA, but its availability is considered essential to devise appropriate strategies for sustainable management of catchments. Both surface water degradation and salt retention are considered to be potential problems in the Lower Orange WMA which may impact on sustainability of agriculture. A study of water quality of the Orange River confirmed increases in salt concentration downstream from the Gariep Dam (121 mg L-1) to the Orange River Mouth (326 mg L-1) in 1995 and expressed special concern about the increase in salinity between Boegoeberg and Kakamas. Simulation using the Water Quality Model for the Orange River Catchment furthermore projected that by 2030, salt concentration would increase by about 25% at Boegoeberg Dam and Kakamas. This is ascribed to the effect of irrigation return flow from the Boegoeberg area on the reduced flow in the river. In the river reach from Boegoeberg Dam to Onseepkans, where grapes represent 90% of the crop value, the actual salt concentration regularly exceeds 500 mg L-1 (0.77 dS m-1), but remains below 750 mg L-1 (1.15 dS m-1) on all but a few occasions. From an interpretation of available salinity guidelines, this study concluded that since the periods when salt concentration increases beyond 750 mg L-1 are of short duration, this should not have a long-term effect on permanent crops. Salinity research on grapevines in the Breede River Valley, however, indicated that grapevines are more sensitive to salinity than suggested by international salinity guidelines. This is important information to consider when evaluating the effect of salinity on crop production. The water quality situation downstream of Vioolsdrift was furthermore identified as a definite cause for concern and may have international implications as the Orange River is shared between South Africa and Namibia over hundreds of kilometers.