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Surprisingly optimistic!
12,441 Posts
Discussion Starter #1
"Geological challenges in constructing the proposed Geba dam site, northern Ethiopia"

Objective: This initiative is intended to inspire citizens longing to see Mekelle's advancement towards becoming a world class city. Implementation of this proposal is one addition that would excel the development and growth of Mekelle city.
ቀንዲ ሽቶ ናዚ ተበግሶ እዚ ምስቲ ኣብ ሃገርና ዘሎ ዘይቀሃመ ሃይሃይታ ልምዓት ሓዱሽ ሓስብ ብምምንጫው ኩሎም ግዱሳት ዘጋታትና ሙሁራትናን ከምኡዉን መራሕትናን ብዝሓየለ ንልምዓት ንምጉስጓስን ዘለና ፀጋታት ኣብ ጥቅሚ ንከዉዕልዎ ንምልዕዓል እዩ። አንሆ ድማ ክምቲ ኣብ መእተዊ ዝተጠቐሰ ኣብ ዉሽጢን ኣብ ወፃእን ዝርከቡ ብዙሓት ኣሕዋትናን ዓሓትናን ርእሰ ከተማ ክልልና ዝኾነት ዉቅብቲ መቐለ ንምርኣይ ሃረር ኢሎም ይረኣዪ ኣለዉ። እዚ ሰናይ ተበግሶ ናብ ኵዉንነት ንምላዋጥ ግን ሃረርታ ጥራሕ እኹል ኣይኮነን:: ካብ መራሕቲ ክልልና ጀሚሩ ዉቅብትን በልፅትን መቐለ ንምራይ ዝሕልን ኩሉ ክረባለበሉ ይግባእ ብምባል ይላቦ።

Fig1. Image from Google satellite map and map with terrain including proposed lake (taken on 06/21/2011)(click on image to see enlarged view)
Lake Mekelle/Geba Reservoir statistics ( ኣገደስቲ ሓበረታታት )
· Location (ዝርከበሉ ቦታ): Northern Ethiopia, Tigray Region (ሰሜን እትዮጵያ, ከልል ትግራይ)
· Coordinates(ኩርንዓት ኣብ ምድሪ): 13°38’N 39°25’E Coordinates

Fig.2 coordinates; longitude and latitude of the proposed lake (click on image to see enlarged view)
· Lake type(ዓይነት ቃላይ): Reservoir (ሰብ ስራሕ ሓፅቢ/ ዲጋ/ግድብ)
· Basin country(ዋሕዚ /መገብቲ ሩባታት ዝርከበሉ ሃገር): Ethiopia (ኢትዮጵያ)
· Surface area(ስፍሓት ዝሽፍኖ መሬት): 106km2/10600hectares
- This is over 5X the size of lake Hashenge.
- Quite a few number of locals will be displaced.
- Mekelle-AbiyAdi road will be realigned preferably over the crest of the dam which potentially avoids dropping and picking altitude over the road course around the Geba gorge.

Fig. 3. Outlet of Geba River and inlets of the five Geba tributaries. For relative visualization, the origin (0,0 ) is set at the roundabout in front of Mekelle city municipality. The dam site is some 14km west of the origin. (click on image to see enlarged view)
· Surface elevation (ብራኸ ከብዲ ቓላይ): 1900 meters
It is possible to shrink or enlarge the size of the lake by decreasing or increasing the surface elevation. Remember the dam height will decrease or increase respectively. @ 1900 meters of surface elevation, with the exception of Mekelle-AbiyAdi road, the lake will not be in conflict with other existing infrastructures. Messebo Cement Factory will not be affected at all, which will be roughly 3.048km east from the water. Water yield of the 5 tributaries permitting, the achieved lake will not be too big nor too small to build. It is just about right, at least to my sense. Size of the lake is not something that can be upgraded later. So sensible decision should be done at the start.

Fig. 4. Geba River as seen north just south of the proposed dam site. The green arrow shows altitude of 1900meters. (image taken from Google earth on 06/28/11) (click on image to see enlarged view)
· Perimeter(ስፍሓት ከብዲ ቓላይ): 226km
A 226km of waterfront line can be developed to waterfront properties with and without private access to the water, in addition to numerous view properties. This will attract real estate investors, builders, and buyers which will stir the local economy in creating jobs and encourage businesses. It will definitely generate humongous revenue to the city for generations to come. A master plan developed should be adhered at all cost. In order to avoid contamination of the lake, sewage system should be adopted and septic shouldn't be permitted to developments within a few distance to the lake. The waterfront line should compromise the following.
1. Few waterfront properties with private access for business such as a resort hotel, boatyard, boat launching etc…
2. Substantial waterfront properties with private access for residence (north side of the lake on the banks of the three narrow branched extensions of the lake)
3. The public shouldn’t be denied majority of water front access. With the development of parks and hiking trails around most part of the lake, waterfront should be for the enjoyment of the public.
4. A limited number of floating house community should be allowed with strict rules and regulations.
· Crest of dam (ዉርዲ ግድብ): 1250 meters

Fig. 5. The red line shows the possible crest line (image taken from Google map on 06/29/11) (click on image to see enlarged view)
· Dam height (ቁመት ግድብ): 250 meters
Lake Mekelle/Geba reservoir can be created by constructing a dam across the Geba River. Surplus/flood water during the rainy season will be collected to create the lake. At air distance of some 14km west from the roundabout in front of Mekelle City Municipality, the dam can be earth dam with water discharging structure (cheaper?). The twisting nature of the river course at the proposed dam site and the fact that the river flows in a deep gorge is advantageous to build an earth dam even if it will score a height of up to 250 meters measured from the river bed. Quarry of fill material (if suitable) can be developed atop the hill on both side of the gorge at the dam site. The fill material can be lowered to the gorge using hauling technologies such as conveyor belts that potentially reduces the use of dump trucks that would cut cost.
Both the reservoir and dam at Tekeze are threatened by increasing sedimentation caused by environmental degradation upstream. Even though Geba River is not one that contribute its share towards this problem for now, it will be for future developments.

“Geba (drainage area: 5180 km²), is a tributary of the Tekeze river. The catchments had drainage areas between 120 km² and 4330 km² (mean: 1068 km²) and represented a range of environments. Annual rainfall ranges from 700 mm to more than 1200 mm. The estimated area-specific sediment yields (SY) varied between 400 and 2500 ton/km²/yr (average: 1404 ton/km²/yr).”
The table below is an “Overview of the Total Runoff and Sediment Export during the measuring period (12/07/2006-10/09/2006) and their uncertainties. ‘Error’ refers to the relative error on the calculations and was assed by Monte Carlo simulations. ‘% predicted’ refers to the share of the total runoff/SY that was predicted, based on rainfall data. These predictions could not be validated. Values for Middle Geba are probably over predicted.”

The image above followed by thoughts are taken from study conducted by Physical and Regional Geography Research Group, Catholic University of Leuven in collaboration with Mekelle University. To learn more follow the link M_Magnitude and dynamics.pdf
The first five catchment listed on the table drain to the proposed Geba river dam; hence fractionally avoiding sedimentation problem downstream at Tekeze.
2.1. Tourism industry
Located close to the Regional capital Mekelle, Lake Mekelle will attract tourists and city-dwellers creating a new form of industry that can engage locals in business such as resorts, fishing, boatyard, boat launching, marina, diving sports etc... There will be a variety of marine life and birds around the lake.
2.2. Appreciated value of properties
The presence of water body near the city will boost dwelling preference that would drive up the supply of properties. This will generate substantial revenue for the city through lease income and property tax.
The water table around the lake will rise which has a positive impact on the environment. Mekelle city water supply depends mostly on deep water wells. Rising water table might improve the yield of water wells. This all depends on the geological aspect of the Geba basin around the proposed lake. The degree of water seepage and other geological factors will also determine the realization of the lake. In addition to a feed to the water wells, water from the dam can be diverted to a water treatment plant for Mekelle city water supply. Below is a helpful link of studies conducted on the geology of Geba basin available on the World Wide Web. Map.pdf
Parallel to the benefits harvested above, the situation will create a hydro power generation potential that can run side by side to the existing benefits. Since the lake is not intended primarily for power generation, in order to utilize it for power, the overflow/surplus water should only be used for such purposes. This will keep the lake at the said elevation (1900) through out the year. If the elevation is volatile because of the use of excessive water for power generation, the primary reason of creating the lake would be impossible.
Based on my limited understanding, I feel that the very basic portion of the proposed initiative includes cost of relocating people, cost of constructing the earth dam (if cheaper?) that includes some sort of water discharging structure, and cost of realigning Mekelle-AbiyAdi road. Then follows the rest gadgets such as dealing with the pollution coming via May-Illala since it drains to the lake.Two kinds of major pollution threats which are industrial and biological are anticipated. Industrial being the worst, biological threats are some how dealt by the environment itself to some extent. I had no doubt that if there exists any industrial pollution, it can be solved by enforcing codes with out incurring additional cost whether or not this initiative is implemented. Any other pollutions such as biological waste(if any) would cost Mekelle City Adminstration as two major works has to be done. The first is to assure that storm drains of the city are free from any possible contamination of biological waste. The second thing is a whole big story that there should be waste/sewer line that collects biological waste and convey it to waste treatment plant where the waste is processed. Lets anxiously wait until pro's give us some insight.
Different departments of the city that include Works and Urban Development Bureau, Water Supply and Sewer services, Parks Administration and others which benefit primarily from this project should be steak holders. EEPCO (Ethiopian Electric Power Corporation) which benefits from the side project of power generation in addition to ease of sedimentation on future Tekeze River projects should be a steak holder. Mekelle University should potentially use the lake for existing faculties and new faculties that will be created tuned around marine life. This will put the university to be part of the steak holders. The ultimate beneficiary who is the general public should also play an important role for the implementation of this project.
It has been months since this initiative is posted. Thousands of people have viewed it from different parts of the world. As far as I know, there is none official response from local authorities. One thing that concern any citizen should not be why it is not done right away. Rather, it will be a great failure if action, that paves the way to develop this initiative, is not taken today. Any lucky generation (today's generation had a great opportunity) will do it any time. Authorities and citizens should strive at least to accomplish the necessary detail studies on the possibility of the lake. If the feasibility of the lake is positive, even if it is not constructed right away, it can be included in the master plan so that the area will be preserved with out any developments. Not all cities and towns are blessed with such opportunity. Mekelle city's great opportunity should not be ruined.
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Surprisingly optimistic!
12,441 Posts
Discussion Starter #2
In Ethiopia efforts to alleviate the problem are being made by both the federal government and local administrative bodies, including the proposed Geba dam to be built across the Geba River, 25 km northwest of Mekelle city (Fig. 1). The dam will have a crest length of 1,000 m, a height of 80 m and a reservoir capacity of 350 million cubic metres. It is designed both to supply water to the city and surrounding populations and to regulate the flow of the river. Currently, Mekelle city is supplied with groundwater mainly from the Aynalem well field, some 5 km to the south east. In 1998, 11 wells were drilled and pump tested for 72 h. It was concluded that total output was some 220 l/s, with each well providing between 15 and 30 l/s. However, since 2002, the water level has declined continuously (Water Works Design and Supervision Enterprise, WWDSE 2007).

3,989 Posts

Apparently, it will be a large dam with a much reservoir larger than the city of Mekelle itself. I wonder why the project does not include generation of electricity which could have easily produced 100 megawatts.

708 Posts
How can you use the reservoir for electricity if you need to use the water for residential and industrial use? If you use it for electricity, the water would flow away.
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