Shimelis Behailu Dessu

Comparing flow regime, channel hydraulics, and biological communities to infer flow–ecology relationships in the Mara River of Kenya and Tanzania

Abstract Equatorial rivers of East Africa exhibit unusually complex seasonal and inter-annual flow regimes, and aquatic and adjacent terrestrial organisms have adapted to cope with this flow variability. This study examined the annual flow regime over the past 40 years for three gauging stations on the Mara River in Kenya and Tanzania, which is of international importance because it is the only perennial river traversing the Mara-Serengeti ecoregion. Select environmental flow components were quantified and converted to ecologically relevant hydraulic variables. Vegetation, macroinvertebrates, and fish were collected and identified at target study sites during low and high flows. The results were compared with available knowledge of the life histories and flow sensitivities of the riverine communities to infer flow–ecology relationships. Management implications are discussed, including the need to preserve a dynamic environmental flow regime to protect ecosystems in the region. The results for the Mara may serve as a useful model for river basins of the wider equatorial East Africa region. Editor Z.W. Kundzewicz; Guest editor M. Acreman Citation McClain, M.E., Subalusky, A.L., Anderson, E.P., Dessu, S.B., Melesse, A.M., Ndomba, P.M., Mtamba, J.O.D., Tamatamah, R.A., and Mligo, C., 2014. Comparing flow regime, channel hydraulics and biological communities to infer flow–ecology relationships in the Mara River of Kenya and Tanzania. Hydrological Sciences Journal, 59 (3–4), 801–819.

Effects of sea-level rise and freshwater management on long-term water levels and water quality in the Florida Coastal Everglades

Since the 1880s, hydrological modification of the Greater Florida Everglades has reduced water levels and flows in Everglades National Park (ENP). The Comprehensive Everglades Restoration Program (CERP) began in 2000 to restore pre-drainage flows and preserve the natural landscape of the Everglades. However, sea-level rise (SLR) was not considered in the development of CERP. We used long-term data (2001-2016) from the Florida Coastal Everglades-Long Term Ecological Research Program to quantify and model the spatial dynamics of water levels, salinity, and nutrients in response to changes in climate, freshwater management and SLR in the Shark River Slough (SRS), ENP. Results indicate that fresh-to-marine head difference (FMHD) was the single most important factor affecting marine-to-freshwater hydrologic connectivity and transport of salinity and phosphorous upstream from the Gulf of Mexico. Sea-level has increasingly exceeded ground surface elevation at the most downstream freshwater site in SRS, thereby reducing the FMHD. We showed a higher impact of SLR in the dry season when there was practically no freshwater inflow to raise FMHD. We also demonstrated effectiveness of inflow depends more on the monthly distribution than the total annual volume. Hence, the impact per unit volume of inflow is significantly higher in the dry season in preventing high salinity and marine-derived nutrient levels. We advocate that FMHD needs to be factored into water management decisions to reduce adverse and likely irreversible effects of SLR throughout the Everglades landscape.

Evaluation and Comparison of Satellite and GCM Rainfall Estimates for the Mara River Basin, Kenya/Tanzania

Water resources and climate change studies in data-scarce regions of the world are increasingly employing satellite rainfall estimates (RFEs) and rainfall outputs from general circulations models (GCMs). The reliability of these data sources is seldom verified with observed data prior to application. This chapter outlines the application of simple evaluation techniques to assess the potential of RFE and GCMs outputs as a potential rainfall information sources in the Mara River basin (MRB), Kenya/Tanzania. Results of the assessment show that proper care is required in comparing/mixing of results from studies using different RFE in the MRB. In general, RFE and GCMs are promising sources of information, but refining the estimates with a much improved algorithms is essential.

Climate Change Impact on Sediment Yield in the Upper Gilgel Abay Catchment, Blue Nile Basin, Ethiopia

According to Intergovernmental Panel on Climate Change (IPCC) future projections, precipitation and temperature will increase over eastern Africa in the coming century. This chapter presents basin-level impact of climate change on sediment yield in Upper Gilgel Abay catchment, Blue Nile Basin, Ethiopia, by downscaling HadCM3 global climate model using Statistical Downscaling Model (SDSM). IPCC-recommended baseline period (1961–1990) was used for baseline scenario analysis. Future scenario analysis was performed for the 2020s, 2050s, and 2080s. Globally, HadCM3 model is widely applied for climate change studies and it consists of A2 (medium high emission) and B2 (medium low emission) scenarios. Impact assessment on sediment yield was done by Soil and Water Assessment Tool (SWAT) hydrological model. SWAT model performance in simulating daily sediment yield for the study area was satisfactory with Nash–Sutcliffe Efficiency (NSE) of 0.58 and 0.51 for calibration and validation periods, respectively. Mean annual changes of precipitation and temperature (maximum and minimum) were applied to quantify these impacts. The result of downscaled precipitation and temperature reveals a systematic increase in all future time periods for both A2 and B2 scenarios. These increases in climate variables are expected to result in increase in mean annual sediment yield of 11.3, 16.3, and 21.3 % for A2 scenario and by 11.0, 14.3, and 11.3 % for B2 scenario for the 2020s, 2050s, and 2080s, respectively. This increase in sediment yield is double the increase in stream flow due to climate change for all time periods. Future work need to consider also impact of land use change on the catchment for future sustainable development plan.

Climate Change Impact on Stream Flow in the Upper Gilgel Abay Catchment, Blue Nile basin, Ethiopia

According to Intergovernmental Panel on Climate Change (IPCC ) future projections , precipitation and temperature will increase over eastern Africa in the coming century. This chapter presents basin-level impact of climate change on stream flow in Upper Gilgel Abay catchment , Blue Nile basin, Ethiopia , by downscaling HadCM3 global climate model (GCM) using statistical downscaling model (SDSM). IPCC recommended baseline period (1961–1990) was used for analysis of baseline scenario. For future scenario analysis time periods of the 2020s, 2050s and 2080s were used. Globally, HadCM3 model is widely applied for climate change studies and it contains A2 (medium–high emission) and B2 (medium–low emission) scenarios. The impact assessment on stream flow was done using the soil and water assessment tool (SWAT ) hydrological model. The performance of SWAT model in simulating the stream flow was shown with a Nash–Sutcliffe Efficiency (NSE) of 0.76 and 0.78 for calibration and validation periods, respectively. Mean annual changes of precipitation and temperature (maximum and minimum) were applied to quantify these impacts. The result of downscaled precipitation and temperature reveals a systematic increase in all future time periods for both A2 and B2 scenarios. These increases in climate variables are expected to increase mean annual stream flow by 7.1, 9.7, and 10.1 % for A2 scenario and by 6.8, 7.9, and 6.4 % for B2 scenario for 2020s, 2050s, and 2080s, respectively. Future work need to consider impact of land use change on the catchment for future sustainable development plan.

Groundwater Recharge and Contribution to the Tana Sub-basin, Upper Blue Nile Basin, Ethiopia

The Tana sub-basin exhibits one of the huge groundwater reserve zones in Ethiopia. While there is effective three months of precipitation, Lake Tana receives year-round recharge from the four major rivers in the sub-basin: Gilgel Abay, Gumara, Ribb, and Megech . Hence, the groundwater contribution to the Lake Tana is quite important to the aquifer-dependent ecosystem and environmental flow requirement in the area. However, the contribution of the groundwater resource to the Lake Tana water body is not well studied, and useful information for development planning and management is not available. The purpose of this study was to develop information that can better inform decision making on groundwater abstraction and/or lake water uses in the Tana sub-basin considering the volume of the groundwater contribution to the Lake Tana water body. Accordingly, the study combined stream flow simulation and baseflow separation. The stream flows at the junction of the lake water body are generated by the application of Soil and Water Assessment Tool (SWAT). The groundwater contribution of the streams is defined by baseflow separation using a reclusive digital filter method. The groundwater contribution to the Lake Tana water is through lateral flow from the vadose zone and return flow to shallow aquifers. The contribution of the four major rivers’ catchment area; Gilgel Abay, Gumera, Ribb, and Megech Rivers, is 718, 414, 451, and 350 mm/year, respectively. This accounts up to 60 % of the total annual in flow to the Lake Tana water body through stream flow.

Flood Forecasting and Stream Flow Simulation of the Upper Awash River Basin, Ethiopia Using Geospatial Stream Flow Model (GeoSFM)

The Geospatial Stream Flow Model (GeoSFM) has been widely applied in data scarce regions for flood forecasting and stream flow simulation with remotely acquired data. GeoSFM was applied in the Upper Awash River basin (UARB) with observed input data set. GeoSFM sensitivity to observed input data quality, subbasin partition, and change in parameter were investigated. Results demonstrated that GeoSFM is sensitive to the size and number of subbasins. Among the eight model parameters, the basin loss and curve number are the most sensitive in UARB. GeoSFM evaluation using a split sample of 10 years observed daily discharge showed satisfactory performance, Nash-Sutcliff Efficiency 0.67 and 0.70, coefficient of determination, 0.60 and 0.65 for calibration and validation, respectively. The monthly average simulation captured 76 % of the observed variability over 10 years. Comparative analysis suggested increasing partitions improves performance in capturing flooding events and the single basin scenario can potentially be used for flood forecasting or resource assessment purposes. The 60 % coverage of vertisol in the basin and low quality of observed data affected model performance. Further evaluation of GeoSFM in heterogeneous soil type and land use/cover can help to identify the influence of dominant physical characteristics. In general, GeoSFM offers a competent platform for stream flow simulation and water resource assessment in data scarce regions.

The Nile River and Transboundary Water Rights

The Nile River is a transboundary river shared by 11 countries: Burundi, Egypt, Democratic Republic of the Congo, Eritrea, Ethiopia, Kenya, Rwanda, South Sudan, Sudan, Tanzania and Uganda. Among the riparian countries, Ethiopia is the largest contributor to the Nile River accounting to 82% of the annual flow. Nile River water rights are complex as a result of the basins geography climate and political history. Pre-colonial, colonial and post-colonial claims and assertions of water rights are being challenged due to growing population, awareness and water demand. The Blue Nile is the largest of the tributaries, a collection of tributaries in the Ethiopian Highlands, flowing through settlements, farm fields and natural landscapes. Water demand in the basin is continuously growing as a result of population growth, climatic factors, and small to medium scale irrigation and water harvesting schemes. Small dams and control structures are being built on tributary rivers for both hydropower and irrigation. Ethiopia has been investing on multiple dams on Nile river tributaries and is building a major dam, the Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile since 2011. Although, there are over thirty dams and water control structures on the Nile and tributaries, dams on the Blue Nile raise attention as it is the main source of water for the Nile, The GERD has brought to the forefront the question of water rights of the Nile with a tug of war between Ethiopia and Egypt with the main concern of downstream flow reduction as the result of the dam. Negotiations and agreements have been murky as water rights and water sharing is not addressed directly. This chapter outlines the history of water rights, water use and water controls in the Nile basin, and current realities associated with the construction and operation of the GERD.

The Grand Ethiopian Renaissance Dam on the Blue Nile

The Nile Basin is one of the largest basins in the world shared by eleven countries. The principal tributaries of the Nile River are theWhite Nile, flowing from the Great Lakes region of Central Africa and the Blue Nile (Abay), Sobat (BaroAkobo) and the Atbara (Tekeze), flowing from the highlands of Ethiopia. Ethiopia contributes close to 85% of the Nile river flow. The Nile basin is entering into a new era of challenges and opportunities primarily driven by population explosion, food and water shortage, increase in water demand and water use, climate change, and complicated water right issues. More importantly, upstream countries started to assert their right to develop the Nile water resources challenging the long-held water right hegemony of Egypt and Sudan. Ethiopia unilaterally launched the construction of Grand Ethiopian Renaissance Dam (GERD). The sheer size and storage capacity of GERD has initiated dialogue and diplomacy towards understanding of the current reality in the basin as well as the absolute need of co-operative water resource development. This chapter provides an overview to the Nile basin along with the social, economic, environmental and political implication of GERD. The book mainly focuses on the Blue Nile basin, the GERD design, filling and operation in association with the larger Nile basin.

Grand Ethiopian Renaissance Dam Analysis

The Grand Ethiopian Renaissance Dam is the first major dam in the Blue Nile (Abay) River of Ethiopia. GERD is a combination of 175 m high roller compacted concrete gravity dam and a 50 m high concrete faced rock fill saddle dam under construction by Ethiopia. The gravity dam is built across the natural course of the Blue Nile River and the saddle dam provides the design storage and water level due to the relatively low relief of the dam site. The dam is being built at the most downstream site of one of the four potential dam sites proposed by a 1964 feasibility study of the Blue Nile basin development conducted by United States Bureau of Reclamation. The dam has been under construction since 2011 with 70% completed at the beginning of 2018. The installed power generation capacity of 6,000 MW is expected to be generated by 16 Francis Turbines each with 375 MW capacity located at the foot of the main dam. The design flow rate of 4305 m3 s−1 is about 3 times the average flow. At the average flow rate, the expected average annual energy production is 15,700 GWH. The suitability of the dam site, dam design, major components and operations are discussed.