THE POTENTIAL OF SAND & SUBSURFACE DAMS FOR RWH IRRIGATION IN DRY LANDS

Transcription

1 THE POTENTIAL OF SAND & SUBSURFACE DAMS FOR RWH IRRIGATION IN DRY LANDS 5 th AUGUST, 2014 ESKINDER FELEKE

2 OUTLINE: About RAIN Foundation Ground water damming Sand and subsurface dams Suitability of SD & SSD in Ethiopia

3 RAIN FOUNDATION: Found in 2003 Our focus is making the concept and practice of RWH familiar to people in areas that lack sufficient and safe water resources Works with partners to develop, spread and implement RWH systems for domestic, productive or environmental uses The THREE services of RAIN: - Advice:- provide concrete advice on all elements of RWH programs and projects - Intelligence or knowledge:- Spread knowledge - Implement:- develop and manages programs and projects

4 WHERE WE WORK: The Netherlands (HQ) Ethiopia Nepal Burkina Faso Mali Senegal Kenya Uganda

5 RAIN IN ETHIOPIA: Implementation: Sand and subsurface dams, RWH tanks, Birka, roof tops We work in Borena, Dire Dawa, Shinile, East & West Harege, Konso, Hamere, Debrezeyit, Work with: AFD, HCS, DEC, SEPDA, ERHA, MU, IWMI, MetaMeta, EWA, HoARC R & D: Traditional technologies, 3R, Best practices Capacity buildings: Knowledge sharing: Dgroup-/communities of practice/ (water4food), SEARNET Documentation and Promotion

6 GROUND WATER DAMMING HISTORY: The damming of water in sand rivers took place in North Africa some 2,000 years ago and in Arizona in the 1700s (Nilsson. 1988). Subsurface dams built in Tanganyika Railway to provide water for their steam locomotives around Thousands of sand dams built by various projects in Machakos and Kitui. From 1974 in Eastern Ethiopia- Dire Dawa (Adada, Ejaneni, Melka Belina, Gende Bira, Melka Jebdu ) & Gursum

7 BASIC PRINCIPLES: Storing water underground instead of storing it in surface reservoirs Storing water in the pore space of the aquifer in the riverbed and riverbanks It is composed of a cut-off wall by which the groundwater flow is dammed, Needs impervious formation below the ground water Water extraction by facilities (wells, intake shaft and pumps) or gravity flow Recharged in rainy seasons

8 WATER STORAGE: Water is stored in empty spaces between sand (voids) which are filled when a dry riverbed is flooded. The courser the sand the higher the volume of water that can be extracte Silt Fine Sand Medium Sand Coarse Sand Size (mm) < to to to 5.0 Saturation 38% 40% 41% 45% Water extraction 5% 19% 25% 35%

9 ADVANTAGES OVER SURFACE DAMMING: Loss of water due to evaporation is almost nil Contamination by insects and animals cannot take place Health hazards such as mosquito breeding are avoided It increases the capacity of traditional wells & boreholes Buffering It does not waste agricultural land because it is underground Siltation is not a problem for groundwater dams Maintenance is simple

10 FUNCTIONS: Increasing the water availability by storing water in the riverbed and banks for MUS Sand harvesting and rehabilitating of gullies Regional groundwater recharge: - In case of cascade of sand dams can cause a general rise in ground water levels in a larger area. -`it can also low yielding and dry up recharge boreholes

11 TYPES AND DIFFERENCES: 1.Sand dam 2.Subsurface dam Sand dam is located above the ground and subsurface below, It has additional components like apron, spillway etc Used when the topographical gradient is high Subsurface dams are located fully below the surface It only uses the storage capacity under the surface while with sand dam storage can be increased by increasing the dam height It isn t exposed to forces of flowing water no flooding risk Can be constructed with local materials (clay soils) It can be constructed by local community with minimum trainings

12 SAND DAM: It s an impervious barrier in a seasonal riverbed A dam constructed above ground (sand bed level). Used to store sand and part of the flood water transported during periods of flooding. It is constructed in layers to allow sand to be deposited and finer material be washed

13 HOW DOES IT WORKS: Sand storage dams aim to delay the quick runoff out of the area, Upstream coarse sediment accumulates, enlarging the sand layer of the riverbed, Part of flood water is dammed & allowed to deposit in front of the dam and water is stored in these sand deposit.

14 IN WET SEASON: IN DRY SEASON:

15 TYPES OF SD: Base on the type of construction materials used; Stone masonry: A dam built of concrete blocks or stones It is also durable and suitable for relatively high dam height (25m Max.) Reinforced concrete: A dam consisting of a thin wall made of reinforced concrete It is a durable structure It s relatively expensive but suitable for any dam height Earthen made dam: A dam consisting of impermeable soil material (mostly clay or black soils) Although earth dams are most cost-effective, they cannot store large quantities of water which makes them less suitable An earth dam can easily be damaged and even destroyed by underground flow Earth dams are not popular and are seldom used (only for minor works)

16 MASONRY CONCRETE

17 BASIC COMPONENTS OF SD

18 SUBSURFACE DAM: It is under ground water dam Structure that intercept or obstruct the natural flow of groundwater or base flow and provide storage for water underground The Maximum storage volume remains the same overtime Used in areas where flows of groundwater vary considerably during the course of the year, from very high flows following rain to negligible flows during the dry season

19 TYPES OF SSD: Base on the type of construction material used there are six type of subsurface dams; Clay or soil Burnt bricks Masonry Concrete blocks Reinforced concrete and Geo-membrane

20 SD/SS DAMS IN ETHIOPIA: First Phase EPID of MOA Concentrated in selected river basin Focus on SWC, water storage & Agriculture Second Phase EWWCA/ SIDA Experience sharing in Kenya Machakos & Kitui Districts 1983 Focus on Water supply & irrigation Third phase 1993-todate NGO & MoWR (Regional Govt) Additional means of water source Water supply, irrigation, conservation and ground water recharge

21 SOME OF THE DAMS IN EE:. Year Latitude Construct Site Region (N) Longitude (E) ed Constructed by 1 Adada Dire Dawa Pro. Admi ' 16.47" ' 45.17" 1974 EPID 2 Awalle 1 Dire Dawa Pro. Admi ' 40.51" ' 42.01" 1975 EPID 3 Awalle 2 Dire Dawa Pro. Admi ' 34.82" ' 49.25" 1975 EPID 4 Bombas EH, Oromia R ' 36.34" ' 10.68" 1981 EWWCA ERO 5 Gursum EH,Oromia R ' 52.58" ' 59.46" 1982 EWWCA ERO 6 Gendebelina Dire Dawa Pro. Admi ' 58.18" ' 21.04" 1983 EWWCA ERO 7 Ejaneni Dire Dawa Pro. Admi ' 17.28" ' 14.83" 1984 EWWCA ERO 8 Kore Somali R ' 52.58" ' 59.46" 1984 EWWCA ERO 9 Melkajebdu Dire Dawa Pro. Admi ' 10.73" ' 47.12" 1985 EWWCA ERO 10 Lege Birra Dire Dawa Pro. Admi ' 35.40" ' 52.71" 1993 LWF 11 Bishanbahe Dire Dawa Pro. Admi ' 3.88" ' 35.87" 1993 LWF 12 Biyo Gurgur Shinille, Somali R ' 02.82" ' 59.77" 1999 HCS 13 Biyo Kobobe Shinille, Somali R ' 37.44" ' 11.76" 2003 MoWR,Somali R 14 Amaretu Shinille, Somali R ' 37.69" ' 35.62" 2003 MoWR,Somali R 15 Gad Shinille, Somali R ' 35.60" ' 39.20" 2009 HCS

22 SUITABILITY IN ETH.

23 IMPLEMENTATION IN ETHIOPIA: Dire Dawa and Shinle - (GO, ERHA, HCS, LWF etc) East Harerge (Gursum, Chinaksen, Babile) - (GO, ERHA, HCS, LWF etc) Metehara - GTF Borena (AFD, CARE etc) South Omo (AFD, SEPDA) Afar (?)

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