Reservoir sedimentation and its mitigating strategies: a case study of Angereb reservoir (NW Ethiopia)

PurposeThe Angereb dam in northwestern Ethiopia was commissioned in 1997 to serve as a domestic water supply for 25 years. However, its sustainability is being threatened by rapid sedimentation. The overall objective of this study was to understand reservoir sedimentation in this tropical highland watershed and to propose its mitigating strategies that would contribute to the improved planning and management of reservoirs in similar regions.Materials and methodsThe reservoir’s surface area and capacity at every 1-m elevation difference were generated based on point (x, y, z) data collected by bathymetric surveys in 2005 and 2007. Rates of reservoir capacity loss and sediment yield during 1997–2005, 1997–2007, and 2005–2007 were calculated and the life of the reservoir was projected. Then an identification of sediment-mitigating strategies was performed by employing a multicriteria decision analysis technique.Results and discussionThe annual total capacity loss during 1997–2005, 1997–2007, and 2005–2007 was estimated at 4.02%, 3.16%, and 3.03%, respectively, and the relatively decreasing trend is attributed to the impact of limited soil and water conservation practices implemented in the watershed at the later stage of the dam project. Comparison of capacity–elevation–area curves between 2005 and 2007 showed that sediments were distributed across the reservoir floor, though most (68%) deposition occurred below the dead storage level. The actual life of the Angereb reservoir was projected to be 3 years, which means that the remaining dead storage capacity will be silted up completely by the end of the rainy season in 2011. The rapid sedimentation is due to both technical and environmental factors.ConclusionsBoth curative and preventive sediment management strategies were proposed: (1) removal of sediment using machinery or manual labor and promoting use of the sediments for farmland reclamation, and (2) implementation of specific area-targeted watershed management interventions. In the short-term, the reservoir life can be extended by raising the intake level of the pump suction pipe. For sustainable dam and reservoir design, top priority should be given to building a reliable sediment yield database, development and adoption of appropriate methodologies for predicting sediment yield, and capacity building of designers.

[1]  H. Leirs,et al.  Interdisciplinary on-site evaluation of stone bunds to control soil erosion on cropland in Northern Ethiopia , 2004 .

[2]  Sabine E Apitz,et al.  Assessing and Managing Contaminated Sediments: Part I, Developing an Effective Investigation and Risk Evaluation Strategy , 2005, Integrated environmental assessment and management.

[3]  Igor Linkov,et al.  Application of Multicriteria Decision Analysis Tools to Two Contaminated Sediment Case Studies , 2007, Integrated environmental assessment and management.

[4]  Jan Nyssen,et al.  Specific sediment yield in Tigray-Northern Ethiopia: Assessment and semi-quantitative modelling , 2005 .

[5]  Igor Linkov,et al.  Prioritization of sediment management alternatives using stochastic multicriteria acceptability analysis. , 2010, The Science of the total environment.

[6]  J. Poesen,et al.  Factors controlling sediment yield from small intensively cultivated catchments in a temperate humid climate , 2001 .

[7]  Subhrendu K. Pattanayak,et al.  Worth of watersheds: a producer surplus approach for valuing drought mitigation in Eastern Indonesia , 2001, Environment and Development Economics.

[8]  John R. Williams.  Sediment-yield prediction with Universal Equation using runoff energy factor , 1975 .

[9]  Nigussie Haregeweyn,et al.  Testing and evaluation of the agricultural non-point source pollution model (AGNPS) on Augucho catchment, western Hararghe, Ethiopia , 2003 .

[10]  R. Wenning,et al.  Risk‐based decision making to manage contaminated sediments , 2006 .

[11]  F. Lea,et al.  International Commission on Large Dams , 1936, Nature.

[12]  Jan Nyssen,et al.  Reservoirs in Tigray (Northern Ethiopia): characteristics and sediment deposition problems , 2006 .

[13]  Subhrendu K. Pattanayak,et al.  Valuing watershed services: concepts and empirics from southeast Asia , 2004 .

[14]  W. White.  Reservoir sedimentation and flushing , 1990 .

[15]  E. Veldkamp,et al.  Economic valuation of land restoration: The case of exclosures established on communal grazing lands in Tigray, Ethiopia , 2011 .

[16]  D. Walling.  The sediment delivery problem , 1983 .

[17]  F. Shah,et al.  Economics of reservoir sedimentation and sustainable management of dams. , 2001, Journal of environmental management.

[18]  Gerard Govers,et al.  Erosion models: quality of spatial predictions , 2003 .

[19]  W. White,et al.  The feasibility of flushing sediments through reservoirs , 1984 .

[20]  Suk Hyun Kim,et al.  A decision‐analysis approach for contaminated dredged material management in South Korea , 2010, Integrated environmental assessment and management.

[21]  Wcd.  Dams and development: A new framework for decision-making , 2000 .

[22]  H. L. Houérou,et al.  Restoration and rehabilitation of arid and semiarid Mediterranean ecosystems in North Africa and West Asia: a review. , 2000 .

[23]  J. Poesen,et al.  How soil conservation affects the catchment sediment budget – a comprehensive study in the north Ethiopian highlands , 2009 .

[24]  J. Poesen,et al.  Variability of dry sediment bulk density between and within retention ponds and its impact on the calculation of sediment yields , 2001 .

[25]  J. Poesen,et al.  Sediment yield variability in Spain: a quantitative and semiqualitative analysis using reservoir sedimentation rates , 2003 .

[26]  Subhrendu K. Pattanayak,et al.  Ecological and Economic Analysis of Watershed Protection in Eastern Madagascar , 1997 .

[27]  R. Dikau,et al.  Reservoir siltation in the semi‐arid highlands of northern Ethiopia: sediment yield–catchment area relationship and a semi‐quantitative approach for predicting sediment yield , 2006 .

[28]  E Ferguson,et al.  From comparative risk assessment to multi-criteria decision analysis and adaptive management: recent developments and applications. , 2006, Environment international.

[29]  G. Fleming.  DESIGN CURVES FOR SUSPENDED LOAD ESTIMATION. , 1969 .

[30]  John A. Dearing,et al.  Soil erosion on agricultural land. , 1990 .

[31]  J. Dearing.  Sediment yields and sources in a welsh upland lake-catchment during the past 800 years , 1992 .

[32]  E. Veldkamp,et al.  Restoration of Ecosystem Carbon Stocks Following Exclosure Establishment in Communal Grazing Lands in Tigray, Ethiopia , 2011 .

[33]  E. Veldkamp,et al.  Effectiveness of exclosures to restore degraded soils as a result of overgrazing in Tigray, Ethiopia , 2007 .

[34]  J. Deckers,et al.  Rural Poverty Dynamics and Impact of Intervention Programs upon Chronic and Transitory Poverty in Northern Ethiopia , 2010 .

[35]  J. Syvitski,et al.  Geology, Geography, and Humans Battle for Dominance over the Delivery of Fluvial Sediment to the Coastal Ocean , 2007, The Journal of Geology.

[36]  Assessment of sediment distribution pattern in the Tungabhadra reservoir using satellite imagery , 1994 .

[37]  Carl B. Brown,et al.  Discussion of "Sedimentation in Reservoirs" , 1944 .

[38]  Tony Prato,et al.  Multiple attribute decision analysis for ecosystem management , 1999 .

[39]  Mary Logan,et al.  Risk-Based Decision Making to Manage Contaminated Sediments , 2006, Integrated environmental assessment and management.

[40]  Jordan Furnans,et al.  Hydrographic survey methods for determining reservoir volume , 2008, Environ. Model. Softw..

[41]  Jan Nyssen,et al.  Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia , 2010 .

[42]  J. Tavolaro.  A sediment budget study of clamshell dredging and ocean disposal activities in the New York bight , 1984 .

[43]  J. Poesen,et al.  Sediment‐bound nutrient export from micro‐dam catchments in Northern Ethiopia , 2008 .

[44]  Jan Nyssen,et al.  Human impact on the environment in the Ethiopian and Eritrean highlands—a state of the art , 2004 .

[45]  Zhaoyin Wang,et al.  Strategies for managing reservoir sedimentation , 2009 .

[46]  D. Walling.  The response of sediment yields to environmental change , 2009 .

[47]  J. Poesen,et al.  Sediment yield variability in Northern Ethiopia: A quantitative analysis of its controlling factors , 2008 .

[48]  Y. Mohamed,et al.  Sediment management modelling in the Blue Nile Basin using SWAT model , 2011 .

[49]  H. Sichingabula.  Problems of sedimentation in small dams in Zambia , 1997 .

[50]  Adel Guitouni,et al.  Tentative guidelines to help choosing an appropriate MCDA method , 1998, Eur. J. Oper. Res..

[51]  G. Morris,et al.  Reservoir sedimentation handbook : design and management of dams, reservoirs, and watersheds for sustainable use , 1998 .

[52]  Huib Hengsdijk,et al.  Modeling the effect of three soil and water conservation practices in Tigray, Ethiopia , 2005 .

[53]  L. Gaspar,et al.  Reconstructing the history of sediment accumulation in the Yesa reservoir: an approach for management of mountain reservoirs , 2009 .

[54]  W. H. Wischmeier,et al.  Predicting rainfall erosion losses : a guide to conservation planning , 1978 .

[55]  W. Dietrich.  Settling velocity of natural particles , 1982 .

[56]  M. G. Anderson.  Encyclopedia of hydrological sciences. , 2005 .

[57]  Bart Muys,et al.  Sediment deposition and pedogenesis in exclosures in the Tigray highlands, Ethiopia , 2006 .

[58]  A. R. Orme,et al.  The physical geography of Africa , 1997 .

[59]  Melvin J. Dubnick.  Army Corps of Engineers , 1998 .

[60]  J. Poesen,et al.  The sediment delivery problem revisited , 2007 .

[61]  P. Allen,et al.  Multifrequency Acoustic Profiling for Water Reservoir Sedimentation Studies , 1999 .

[62]  M. Jansson.  A global survey of sediment yield , 1988 .

[63]  R. K. Ambers.  USING THE SEDIMENT RECORD IN A WESTERN OREGON FLOOD – CONTROL RESERVOIR TO ASSESS THE INFLUENCE OF STORM HISTORY AND LOGGING ON SEDIMENT YIELD , 2001 .

[64]  O. Slaymaker.  The sediment budget as conceptual framework and management tool , 2003, Hydrobiologia.

[65]  D. Walling.  The sediment yields of African rivers , 1984 .