PROJECT SUMMARY SHEET FOR ROTARY CONSIDERATION 10/21/08
Project Title:Katumoi Area Rainwater Harvesting Dams
Submitted by: Dr. Elijah Korich – Keiyo Soy Ministries
PGWI Champion: Tony Sauder
We are requesting this grant to help construct small dams to harvest rain water and runoff from the hills and mountains which will enable communities to irrigate their small farms or gardens and produce food for their families. ?Some locations will be amenable for constructing small shallow wells in the vicinity of the dams that could provide improved sources of water. ?We are also requesting funds for technical support for dam siting and construction techniques. ?There will be a capacity building component to training the communities on water and sanitation issues and study of construction and maintenance of dams.
Keiyo Soy Ministries (KSM) has had success in providing water to four schools, three shopping centers, and seven communities which have benefited from a 15-mile pipeline of gravity based water system, and two completed storage tanks.? The construction of a third tank will be completed by April 2009.? We have created hope by what we have accomplished in less than 8 years.? The communities are inspired and are taking full ownership and management of this water project. ?The only way we have succeeded is our ability to engage and train the communities to take full responsibility because this is their hope for their children’s future.
|Project Financial Requirements:||$7,500 for technical support and materials and transport for 3 initial dam sites|
|In Kind Provision:||KSM and community will provide up to
half of the cost and in-kind materials valued at more than $6000.
|Number of beneficiaries||3 communities with approximately 30 families (500 people) in this 1st phase|
|Partners in Kenya||KSM representatives, technical support from AIMtech and others with small dam expertise|
|Location Map||See attached|
Remote Sensing for dam sites by PGWI hydrogeologists and coordination of Kenyan dam expertise. ?Site and area visit to select dam sites and begin site preparation and community capacity building by PGWI/KSM team (2+ persons).? PGWI will also determine the feasibility for project expansion and coordination with ongoing water and sanitation efforts.
|Table 1. Small Dam Proposed Project Costs|
|Costs ($)||Costs ($)||In-kind|
|Technical Evaluation and Coordination|
|Topographic maps and remote sensing||250|
|Hydrogeologist site selection visit (travel)||2000||500|
|Kenya Sand Dam expertise||500||100||100|
|Implementation Costs (3 initial dams)|
|All terrain vehicle/materials transport||1500||500|
|Cement, rebar, formwork, non-local materials||3000|
Photos from proposed project area
Woman collecting water from stream bed and watercourse flowing after the rains.? These watercourses go dry and small dams can store water in the subsurface long after the rains have ended.
Map of Kenya showing Eldoret:???????????????????????????????? Terrain Map of Keiyo Valley east of Eldoret:
Project area ranging in elevation from 1500m to 2700m:
There are 2 general methods of employing local materials and adapting existing features to retain precipitation runoff and store water for use once the rainy season has ended.? Subsurface dams can be used in the sand beds of the dry creek beds (wadis) to intercept the shallow groundwater and maintain subsurface storage for abstraction by shallow wells.? Rock and earth micro dams are suitable for locations at the base of the hills where ravines reach the level plains.? The two methods are described in more detail in the following paragraphs along with how they can be employed as a source of water for livestock and dry season agriculture.? Shallow wells can be installed in the vicinity and when properly protected, they can provide an improved source of for domestic use.
Subsurface dams constructed in suitable dry creek or river beds with large sand storage volumes are ideal water retention facilities. Although the stored volume may be less than a surface reservoir, the stored water is protected from direct surface contamination and evaporation is limited, especially in deep coarse sands.? The subsurface dams are best constructed where the sand beds are 5 or more meters wide and 2 or more meters deep.? Local residents often have a good idea where water is retained within the dry creek bed for more than a month after the rains have ended.? These are often good locations to enhance storage with a subsurface dam.? In locations where there is ongoing irrigation of vegetables but the water supply is quickly exhausted, a subsurface dam can help increase the water supply.
Subsurface dams are constructed by excavating down to the least permeable layer of soil or bedrock.? The trench is backfilled with tamped or puddled clay.? In the absence of suitable clay, clayey soils and plastic sheeting can be employed.? Another option is to build an adobe cut-off wall with the upstream side plastered with a rich cement mortar, but this is not very economical.?
The intent of the subsurface dam is to store enough water and to induce recharge into the surrounding soils so that water can be withdrawn from a lined shallow well in the bank of the dry creek.? In cases where the banks consist of clayey soils, an infiltration trench can be excavated and filled with sand to transmit the water to the well.? It is also possible to install a perforated PVC pipe buried in the dry creek bed to transmit the water directly to the well.
The well can be economically constructed using 1 m diameter concrete rings which can be caissoned into the soils beneath the water table.? The rings can be constructed at a central site for quality control and security and then transported to the well sites with donkey carts. ?Examples of typical subsurface sand dams from Rainwater Catchment Systems for Domestic Supply (Gould & Peterson 1999) are shown below:
Rock/Earth Micro Dams
Small dams for intercepting runoff can be located in locations within a ravine to maximize storage and minimize the length of the dam required.? They can also be used to raise the level of the sand dam and increase the storage capacity.? These dams are called micro dams because they are usually limited to 1.5 to 2 meters (m) in height.? When placed in ravines they are intended for small catchments areas of at least 1 km2 in watersheds with steep slopes (+15%).? There might be smaller catchments that are sufficiently rocky with steeper slopes that may generate enough run-off.
Since the basic structure of the dam includes a dry rubble-stone nearly vertical downstream face and are generally designed to overflow over the entire crest, the design and sizing of a spillway is not required.? The site is prepared by excavating a trench to the impermeable basement rock or clayey soil, if encountered.? An impermeable cutoff trench is constructed using clay or clayey soil and plastic sheeting (see figure following this section).? If available, it is preferable to transport water to better compact the clayey soils in the dam structure. ?The top of the dam wall or crest can be finished with a cemented cap or masonry and mortar if suitable large flat rocks are not available.
If the bedrock surface appears to be fractured or if suitable clayey soils can not be obtained in the vicinity, then plastic sheeting can be buried in the bed of the ravine and on the upstream side of the dam.? Due to the expense and potential short life of the plastic sheeting, every effort should be made to select suitable sites.?
A photo of a typical dam and well structure as constructed in Chad is shown below, followed by sketches for dam and well ring construction:
Potential suitable sites for subsurface dams will be identified initially with remote sensing using satellite images or aerial photography if available.? The final locations will be selected based on a prioritization of need, site characteristics and community project ownership.? A survey of dry season water holes and local resident knowledge will be used to identify the best candidates.?? Since an ideal dry creek may have a series of potential locations, the best 3 candidates will be chosen for this first phase of the project.? Each subsurface dam, depending on the site conditions will be expected to take about 2 weeks for a crew of 15 to construct.? The well rings would take a couple of weeks to make and cure by a mason and a helper but could be installed by a crew of 6 in 3 days.
The wells would be placed so that they would be the source of irrigation water for vegetable gardening.? Since it is likely that such wells may be used occasionally for drinking water, it is advisable that the well be constructed with a raised mound of excavated soils so that water will run away from the well.? If there is no potable water source available the wells will be covered and protected with a concrete apron.
Rock/Earth Micro Dams
The dams can be constructed by hand with digging implements, wheel barrows and donkey carts to transport clayey soils and water if needed.? Each dam, depending on its length or size can take 2 to 4 weeks for a crew of 20 to construct.? The only outside materials required would be plastic sheeting, drums to hold water, a few bags of cement and possibly HDPE flexible tubing if irrigation by gravity is possible.
The dams would not be sanitary for potable water use since they will collect a lot of refuse, especially if animals are around or if there are defecation areas upslope.? The sides of the reservoir area should be fenced in with thorns, or other suitable material only allowing access for livestock at the upstream edge of the reservoir. ?Once the rains have ended and there is opportunity for dry season gardening, the vegetable plots can be irrigated using flexible HDPE tubing.? If the dam is not located at a sufficient elevation for gravity irrigation, then the water will have to be carried directly from the reservoir.? Typically suitable dam sites in the ravines do not have suitable locations for a well to extract water filtered by passing through soil.? Stones can be arranged to protect the reservoir banks and to extract water more easily.? In any event, the longer the water body lingers into the dry season, the more potential there is for transmission of water born diseases and contact with the water should be limited.
Subsurface dams that have been installed in other semi-arid regions of Kenya have been reported to have improved the environment and vegetation by inducing infiltration of runoff that would otherwise be lost to evaporation downstream.? In the case of temporary storage of surface water, this water is available for livestock and vegetable irrigation and will be located away from homes.