While Sedimentation is the Main Concern for the country, Ethiopia’s National Flagship Project (GERD) is Set to Generate Power
- Although Ethiopia contributes more than 86 percent of the water share of Abbay (as it is called by the Western world ‘the Nile’), the river does not provide the required economic benefit to the country till now.
- The Grand Ethiopian Renaissance Dam is designed to trap 100 years of sediment inflow, but lack of sediment data and rapid land degradation may result in higher sediment yields than expected.
- The major impediment to sustaining the operation of GERD indefinitely is reservoir sedimentation. Due to its large hydrologic size, essentially all of the sediment that enters the GERD reservoir will be trapped unless turbid density currents can be released.
- About 83 percent of Ethiopia’s population lives in rural areas and many derive their livelihoods from agricultural and environmental resources, primarily rain-fed agriculture and cattle grazing.
- The key underlying strategy is to enhance productivity and economic value through optimal management of the best soils while converting the poorer and steeper soils to woodlands (eg firewood, building materials), pasture, or tree crops.
The national flagship project, the Great Ethiopian Renaissance Dam /GERD/ has successfully completed its preparation to start test power production in the coming days. Sources told Capital Ethiopia that the works on the dam to start test power generation is completed.
In the middle of November 2021 Sileshi Bekele /Ph.D./, Chief Negotiator and Advisor on Trans Boundary Rivers and GERD at the office of the Prime Minister said;
“Ethiopia is in preparation for the pre-power generation of the national flagship project, the Great Ethiopian Renaissance Dam/GERD/ within the maximum time cap of five weeks.”
The dam in its pre-power generation is expected to generate 700 MW. As Sileshi said, the overall construction progress of the dam has now reached 82 percent. As officials from the Ministry of Water and Energy explained that when the dam starts the first production of power it will cover 20 percent of the nation’s demand.
Financed by local sources, the GERD will be capable of producing as much as 5,250 MW of electricity, ranking it as one of the world’s largest dams and by far Africa’s largest dam by electricity production. Ethiopia has made the second filling in the past rainy season. The country has made a stand on equitable water use on the Abay/Nile River that is the source of the GERD.
The GERD is the source of an almost decade-long diplomatic standoff between Ethiopia and downstream nations Egypt and Sudan.
Despite the downstream countries mainly Egypt expressing its concern about its water flow Ethiopia strongly reassured that the project would not have harm on others and the country does not have the intention to affect others. To tackle the concerns, the three countries, Ethiopia, Sudan, and Egypt discussed for years, while the negotiation was interrupted majorly from reasons that mainly come from Egypt.
Ethiopia has also been facilitating comprehensive engagements to address the concerns of the riparian countries since the inception of the construction of the GERD. After discussions on UN Security Council, the three countries have come to the AU-led negotiations and perhaps the negotiations between Egypt, Sudan, and Ethiopia are still suspended since Ethiopia completed the second filling of the GERD.
“Ethiopia has never and will never accept any mediator and will never agree with unfair terms that seek to maintain the hydro hegemony of Egypt and Sudan,” said Sileshi, adding,
“Exerting unnecessary pressure on Ethiopia by intentionally politicizing and internationalizing the matter will not make Ethiopia accept the colonial-era treaty over the Nile River.”
Ethiopia contributes more than 86 percent of the water share for Abay, while the river does not provide the required economic benefit. With some cooperation and wisdom, it was initially possible that the ambitious GERD project could become both a great development project for the Ethiopian people and a model for cooperation between Ethiopia and its neighbors. Instead, the project has become a constant cause for conflict as the various actors vie for regional hegemony. Several senior government officials declined to give official information on the issue.
About Grand Ethiopian Renaissance Dam (GERD)
Key project features
- Reservoir volume: 74,000 Mm³ (original)
- Installed capacity: 6,450 MW
- Date of commissioning: 2022 (expected)
The Grand Ethiopian Renaissance Dam is designed to trap 100 years of sediment inflow. Lack of sediment data and rapid land degradation may result in higher sediment yields than expected. Reduction of sediment inflow through watershed management is key to achieving long-term sustainability. Debre Yakob watershed demonstrates a successful example of economically self-supporting watershed management.
The Grand Ethiopian Renaissance Dam (GERD) is a 6,450 MW hydropower project nearing completion on the Blue Nile in Ethiopia, located about 40 km upstream of the border with Sudan. It will be the largest hydropower project in Africa. Owned and operated by the Ethiopian Electric Power company, the 145-m-tall roller-compacted concrete gravity dam will flood 1,874 km2 at a normal pool elevation of 640 m, and will have a tributary catchment of 172,250 km2. With a volume of 74 km3 (of which 14.8 km3 is dead storage), the reservoir can hold about 1.6 years’ worth of average flow of the Blue Nile – 48.5 km3/yr – at the El Diem gage station, just below the border in Sudan (Conway 1997).
The major impediment to sustaining the operation of GERD indefinitely is reservoir sedimentation. Due to its large hydrologic size, essentially all of the sediment that enters the GERD reservoir will be trapped unless turbid density currents can be released. Given the national importance of the GERD project as a sustainable source of power, together with the economic and social consequences of degraded land use in the watershed, land management to reduce erosion will result in long-term benefits at multiple levels.
For the recent sediment yield reported at El Diem and estimating a specific weight on the order of 1.0 t/m3 for sediment deposits, the reservoir’s dead storage capacity is sufficient to trap ~100 years of inflowing sediment. This is an accepted conventional design criterion, but it does not result in long-term sustainability. At reservoirs with a large capacity: inflow ratio, such as GERD, the feasible methods of sediment management are typically limited to the release of turbid density currents and the reduction of sediment inflow through watershed management. This latter approach is the topic of this case study, which focuses on the Debre Yakob demonstration watershed (‘learning watershed’) in the Lake Tana sub-basin.
Hydrology and Sedimentation
The basin of the upper Blue Nile tributary to the dam drains the Ethiopian highlands. The Blue Nile has a single wet season and the flow is highly seasonal, as shown in figure 1. The Ethiopian highlands range from about 500 to 4,533 m in elevation, with average rainfall varying regionally from 600 to 2,200 mm/year.
Sediment concentration peaks one month prior to the discharge peak. Trend analysis at the El Diem gage showed a 61 percent increase in sediment load, from 91 Mt/yr for the 1980-1992 period to 147 Mt/yr for the 1993-2009 period, and was associated with a significant increase in suspended sediment concentration, especially during the rising limb of the wet season. The recent sediment yield is 835 t/km2/yr across the 176,000 km2 watershed tributary to the El Diem gage. A recent study by the Water and Land Resource Centre (WLRC) using a very detailed modeling approach indicates that sediment entering GERD will be in the order of 287 million M3/year, much higher than previous predictions.
Dams have traditionally been designed under the design life paradigm which entails estimating the sedimentation rate and traps efficiency and provision of sediment storage volume equivalent to the design life (typically 50 to 100 years). This old, common, and incorrect assumption is sediment deposition in the active storage space is as prevalent and common as the dead storage space, particularly in large reservoirs. The benefits of water resource projects oftentimes fall short of original expectations owing to the sedimentation of reservoirs. Globally 1 – 2 percent of the storage volume is lost annually, but in Ethiopia, 2% reservoir siltation will be a conservative estimate.
About 83 percent of Ethiopia’s population lives in rural areas and many derive their livelihoods from agricultural and environmental resources, primarily rain-fed agriculture and cattle grazing. Over 90 percent of the cropland consists of small-scale rain-fed household production systems. Ethiopia’s dramatic population expansion over the last 50 years, and future predictions of a growing population (see figure 2), have placed extreme pressure on the land, resulting in accelerated erosion, soil degradation, and rural impoverishment. Land degradation occurred because the production system was based on continuously expanding land for cultivation, rather than increasing the production per unit area, as described in the Abbay basin (Zeleke and Hurni 2001):
As cultivated land was expanded at the expense of other land use and land cover units, grassland declined, resulting in less available fodder and a decrease in the number and quality of livestock. This led to a shortage of animals required for plowing and transport, as well as to a reduction of income and food from animals and their products. This series of related impacts indirectly affected the traditional land management system. When livestock and fodder were plentiful (in the 1950s), manuring was an important practice in the area. It increased soil fertility and hence production without extra cost to the farmer except for labor. After fodder availability and livestock had decreased, manuring (traditionally called hura) was gradually reduced. Moreover, manure is now in greater demand than ever not only because of the lower number of livestock but also because its use as a source of fuel has increased due to the reduction of fuelwood.
Bare lands were used as grazing land. Livestock was forced to stay on these land units, especially during the cropping season, although there was little for them to feed on. This is one of the practices adopted by farmers when the population grows and land becomes scarce. The farming system remains traditional while most of the grasslands are converted to cultivated lands. In this case, both livestock and cultivation took over marginal lands, eventually leading to even more severe land degradation.
The Ethiopian highlands within the GERD watershed are considered to be one of the severest cases of watershed degradation in the world. Sediment yields in the Lake Tana sub-basin, where the Debre Yakob site is located, average about 2,500 t/km2/yr, and in the areas of highest erosion, hazard sediment yield may be as high as 6,500 t/km2/yr. Areas with the highest erosion potential have been analyzed and identified using the SWAT model, together with climatic time series and GIS spatial databases of soil characteristics.
Reservoir Sedimentation Impact
- Reduces storage and energy production, discharge capacity, and flood attenuation capabilities.
- Safety of dams – increases loads on the dam and gates,
- Damages mechanical equipment (moving parts),
- Creates a wide range of environmental impacts.
Hence it is necessary to account for the loss in active reservoir storage space early on in the life of a project and to recognize its impact on the reliability of water and on flood control.
Lost active storage area in Rosier Dam/Reservoir
- Rosier has been the sediment sink of Abbay before the construction of GERD. Over 122 MCM/yr. reach the border
- Rosier decreased from 3.3 BCM to 1.9 BCM/yr (Lost 1.44 BCM or 40% of the storage in 41 years)
- The total amount of sediment delivered in 41 years was 5 billion tons or 3 BCM.
- Large economic loss to Sudan, in addition to the high maintenance costs of sediment clearance in front of the turbines to facilitate hydropower production Omer, et al 2013
- Rosiere was the first trap to the sediments coming from the upper catchment in Ethiopia before GERD.
- Roseires reservoir has already lost more than one-third of its storage capacity due to sedimentation in the last four decades.
This is a large economic loss to Sudan, in addition to the high maintenance costs of sediment clearance in front of the turbines to facilitate hydropower production. During the flood season, the dam’s turbine intakes become blocked with debris and sediment. After a severe blockage in 1981, which prevented hydropower generation for several days, consultants from USAID were asked to make recommendations on reducing the sediment and debris impacts on reservoir operations. This led to debris clearing and dredging equipment acquisitions in 1982. In 1988, blockage occurred again during the flood season between July and October.
Thus, much more is at stake than the issue of reservoir sedimentation, because the degraded soil conditions result in rural poverty and food insecurity. It is essential to maintain this soil on the farms to support productive and sustainable agriculture, just as it is necessary to keep it out of the reservoir to sustain long-term hydropower production.
Sediment management strategies
- Prevention – retain the soil where it comes from (the field) – SLM
- This also improves the lives of farmers ENTRO (2007) projected that Mandaya reservoir would lose some 40% of its gross storage capacity through sediment deposition within 50 years if not reduced by watershed management or if the Karadobi dam is not constructed (upstream) and traps a considerable amount of sediment.
- To save GERD – upstream cascading dams should be constructed at the earliest possible
The Debre Yakob watershed encompasses about 325 ha and is located at 11º 16’ 59″ N latitude and 37º 13’ 45″ E longitude. Rainfall averages about 2,300 mm/year. It was selected as a ‘learning watershed’ by WLRC in 2012 to serve as a demonstration site for a variety of interventions aimed at improving land management practices in a way that would substantially improve the economic circumstances for farmers, while simultaneously reducing soil erosion. Typical of the region, the Debre Yakob watershed was severely degraded by overgrazing, resulting in soil denudation and gullying. To transform the local watershed, the first order of business, and the greatest challenge, was to achieve a shift from free-grazing across the entire landscape, to the use of enclosures and cut-and-carry feeding of the livestock (figure 3). Without relieving the continuous grazing pressure, it would not be possible to achieve the re-vegetation needed to control erosion.
There was considerable initial skepticism in the Debre Yakob community, which had no prior experience with a cut-and-carry livestock management system. Many believed it would not work. However, by working closely with cooperating farmers in one area of the watershed, and by providing the initial funds to build check dams and plant vegetation to stabilize gullies, it was possible to demonstrate that the check dams would accumulate eroding soil and grow luxuriant vegetation (figure 4a and 4b). By the end of the first wet season, the amount of forage production was exceeding the needs of the livestock that, previously, had barely survived when grazing freely. Feeding in one of the livestock enclosures is shown in figure 5.
The key to long-term success in watershed management lies not in the building of erosion control structures, but in changing the economic activities of the community to embrace sustainable production systems.”
With grazing pressure removed, re-vegetation occurred rapidly in the moist soil held by the check dams. Vegetation also began to recover on the upland soils once the livestock was confined and young plants were not immediately consumed by wandering animals. Vegetative growth enhanced soil infiltration capacity and improved soil structure, leading to higher soil moisture levels and, in turn, more vegetation, establishing a positive feedback loop of land restoration.
By eliminating free grazing and producing sufficient forage to support the livestock, the community saw the benefits of changing their production systems. Attention then turned to enhance the value of farm production through multiple avenues. The most important management strategies employed at Debre Yakob are:
- Gulley rehabilitation coupled with community agreements for livestock management incorporating a zero/controlled grazing system linked to cut-and-carry forage production on closed areas, gullies, farm terraces, and around homesteads.
- Area closures to rehabilitate degraded hills that used to serve as grazing lands even though they were not productive. This requires protecting the land against free grazing (animal exclusion areas as part of the zero-grazing arrangement) but cut-and-carry is allowed through agreements among the communities.
- Homestead development interventions are designed to enhance household income and empower women as well as households. It incorporates sub-components such as home garden, and improved fruit tree agroforestry system, forage plantings around the household compound, introduction of new crops (papaya, avocado which has a good export market, hops for beer which has a good local market, etc.), bee-keeping, small-scale poultry, dairy and animal production, compost-making, fuel-saving stove (figure 6) and improved water sources (shallow well or pond).
- Permanently vegetated soil and water conservation terraces were established between fields and planted with fruit trees and forage bushes to make these ‘conservation’ features economically productive (see Figures 7 and 8).
- Techniques to improve soil moisture capacity and fertility through the use of mulches, composting, etc.
- Small nurseries produce biological materials such as trees, forage bushes, grass, fruit, and other seedlings for transplanting.
At Debre Yakob, the economic benefits to farmers provided by the technology package are clearly evident, not only in terms of increased production but also in purchasing power. Among the earliest signs of improved living standards is the replacement of the thatched roofs with corrugated iron sheets. As development proceeds, financing structures to facilitate productive investment become more important, for example, to allow the purchase of a communal truck to transport products to market instead of selling to a middleman at depressed prices.
While many of these activities do not directly influence soil management, they are all part of a farming technology package that makes responsible land management self-sustaining. The key to long-term success in watershed management lies not in the building of erosion control structures, but in changing the economic activities of the community to embrace sustainable production systems. To be productive and sustainable these systems must retain topsoil on the farm. As a result, erosion control occurs as a natural and self-sustaining product of a successful farming system, as opposed to a top-down program aimed at benefiting a downstream hydropower reservoir and sustained by costly subsidies. The importance of focusing on the household economic unit is underscored by the differences between unsuccessful and successful long-term interventions in Ethiopia (Zeleke 2015):
In the past focus was given only to the rehabilitation of watersheds and less was done on activities that enhance income at the household level. This was proved wrong over time as rehabilitation intervention alone didn’t enhance income within a short time and as a result, many watershed development interventions fell back to previous situations. Over the years we have learned that any watershed development intervention should have economic development interventions as a major component of the watershed development plan and this was best organized in the form of homestead development intervention. We have seen that many households graduated from food insecurity through the combination of rehabilitation and economic development interventions.
The key underlying strategy is to greatly enhance productivity and economic value through optimal management of the best soils while converting the poorer and steeper soils to woodlands (eg firewood, building materials), pasture, or tree crops. Multiple avenues need to be pursued to enable the farmer to enjoy higher income and enhanced economic security, providing self-sustaining economic incentives derived from the land itself which guides farmers to maintain and improve soils and sustain vegetative cover without additional external incentives.
Reducing sediment yield by changing land use requires a significant and sustained effort, potentially requiring the intervention of tens of thousands of small farmers. Realistically, an intervention on this scale can only be achieved through the participation of multiple entities including government, NGOs, and the private sector. In some cases, with small watersheds and known erosion hot-spots, there may be the opportunity for effective unilateral action by the dam owner. However, more typically a watershed management project is not a go-it-alone project for the dam owner but may involve many organizations at multiple levels, from the local community up to the national government level. For example, to address land management issues in the North Fork of the Feather River (California, USA), hydropower owner PG&E joined in a formal memorandum of understanding with 17 other organizations (Morris and Fan 1998).
Hydropower producers can play key roles in this process by using their available funds to help develop and demonstrate viable technology packages and to sustain work at demonstration sites which can then be copied and disseminated throughout the watershed by others through both formal workshops and informal means. An economically successful system is likely to be adopted by others, on their own, given access to the information, and provided learning opportunities. This is already happening at Debre Yakob Learning Watershed.
In selecting project areas for intervention, it is essential to understand the natural background rates of erosion and sediment yield and to select for intervention those areas where the erosion rate has been greatly accelerated by poor land-use practices, and where interventions can be applied successfully and sustainably. Tools such as the SWAT model coupled to GIS databases can be extremely helpful in preparing a sediment budget and identifying areas of greatly accelerated erosion. Equally important is the development of locally-relevant technology packages that are economically self-sustaining.
Watershed management programs are not always successful. Key factors that point to long-term success at Debre Yakob include the development of technology packages that are economically self-supporting because they increase on-farm income, and a climate with sufficient moisture to achieve rapid re-vegetation. The establishment of such learning watersheds in different parts of hydropower catchments helps to educate and change the attitude of local communities, experts, and policy-makers. This facilitates the expansion of successful technology packages into other areas.