KITUI SAND DAMS

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Ground Water Dams.Ground water dams are impermeable structures constructed across ephemeral riversmainly to impede subsurface flow in the riverbed sands. This water flows at a lower ratethan the surface water in the river channels. Thus less interference to the surface flows ofwater in the river channel.Pressure difference in water is responsible for it’s flow. In water, the pressure differenceis created by height difference. However, besides the pressure difference, the media offlow is important in determining the flow speed. For the water to be stored in a material,the material should have pore spaces. In these the water is stored. When these pore spacesare interconnected, there is the connection of waters with different pressure. Water athigher levels will flow to attain equilibrium. Thus creating higher water heads willpromotes flow of water. In building ground water dams and increasing the level ofstorage in the sands raises this level hence promoting the flow to the banks and upstreamthe river from the dam. This mainly increases the storage capacity of the river channel byaccumulating the base flow and storing it in the sand. Since the banks are mainly madeup of soil, infiltration is possible due to the raised water heights in the sands. Rocks thatare porous and permeable also facilitate the flow of the water and its storage. Thus thecritical height of the dam is highly recommended for maximum utility of the dam. Theconnection of this impermeable structure to the impermeable country rock stops all theflow in the channel thus accumulating the subsurface water to the level it finds way out ofthe assumed trough that is filled with sand. Sand is made up of 40% air spaces. Thispercentage of the total volume of sand stored in the channel is considered as water. Dueto the other materials in the banks the amount of time the water is stored in the channelgives it sufficient time to infiltrate to the less permeable materials in the banks and at thebase of the river channel.Water stored in these materials is not exposed to a lot of evaporation thus there is apossibility for it being stored in the material for along time. This makes it possible for thewater stored in these materials to last to the next rainy season. This promotes the stabilityof water in the river channel. Because of water accumulation in a variety of materials,overtime, this level is saturated thus raising the water table in the area. Dams built in aseries interconnect this saturation and create a continuous aquifer in the river channelsides.Dam building involves creation or extension of naturally occurring obstructing materialsfor the ground water flow. Typically, river channels are characterized by presence ofsome portions in the rivers that happen to be the point of last resort for abstracting waterin the driest periods. In other words, water-abstracting points in river channels shift, asthe year gets drier. This shifting is attributed to the existence of these natural barriers andthey shift as the height of these barriers comes near the riverbed surface. The deepestbarriers hold the water for the longest period of the year. This depends on the water restlevel in the sand of the river and the amount of water stored in this sand and also on theamount of abstraction of the water. Thus the bigger the trough between two barriers andthe depth of the barrier determines the amount of water stored in them.20
Sand filling the riverA12 B34CBedrock Beneath the riverbedKey:1, 2, 3, 4. WRL in different periods in different season of the year.A, B, C, Different storage obstruction portions.In 1, The Water Level is just near the surface of the river so water is foundeverywhere.In 2. There is very little water in BIn 3 & 4 Water is found in A & B as the troughs are deepest.The principle behind the functioning of the dams is based on the storage of water in thesand of the river. Sand is good for storage due to its high porosities, which rangesbetween 35-40%. Thus of the total volume of the river basin covered by the sand behindthe dam this percentage is water given that porosity is the ratio of the total volume of thespaces in a material not occupied. The water that infiltrates in the sand takes it up. Thistakes only a small percentage of the flowing water in a river. Thus increasing the volumeof this sand creates a higher storage space for water. Given the prolonged period of timethe water stays in the channel, there is adequate time to allow for both lateral and verticalinfiltration and thus recharging the groundwater resources available. In principle, aridareas never receive enough rainfall to allow groundwater recharge from the surfaceinfiltration. Recharge is mainly from surface waters. This is due to inadequate and shortspans of rainfall. High temperatures in these arid semi –arid areas causes a lot water lossthrough evaporation and thus most surface water bodies store water for a short time.21
Page 1 and 2: SASOL FOUNDATIONFIELD OFFICELIASON
Page 3 and 4: SECTION 1INSTITUTIONAL FACTORS3
Page 5 and 6: Metamorphic and igneous rocks of th
Page 7 and 8: comes in have been the method of ex
Page 9 and 10: Usually, many people only think abo
Page 11 and 12: anticipated sand dam project in the
Page 13 and 14: Cost Of Sand DamsContrary to the po
Page 15 and 16: TrainingTraining is an integral par
Page 17 and 18: Each site gives 5 participants for
Page 19: SECTION 11TECHNICAL CONSTRUCTION AN
Page 23 and 24: infiltration, surface flow begins a
Page 25 and 26: decreases leading to a rise in the
Page 27 and 28: ∆i = ϖ =∆xwfxf− wi− xi‘K
Page 29 and 30: Discharge.This is the water that fl
Page 31 and 32: Soft Porous MaterialParent rockNatu
Page 33 and 34: It is assumed that the channel is a
Page 35 and 36: A, B, C Represent different energy
Page 37 and 38: Cross section area of dam is = A dA
Page 39 and 40: ) Pre Hydraulic Design.At this stag
Page 41 and 42: L j = Hydraulic Length.This length
Page 43 and 44: CONSTRUCTION.Setting the trench.Thi
Page 45 and 46: avoid filling the reservoir upstrea
Page 47 and 48: 5) Masonry comprising Hard core and
Page 49 and 50: 0.5mSection X-X49
Page 51 and 52: 0.73m56 26 30.73mH dH d1.0m 1.0m1 4
Page 53 and 54: Plan and section view of the finish
Page 55 and 56: Key.1 W dc 75cm when off the ground
Page 57 and 58: VOLUME DERIVED FORMULAS FOR MAJOR D
Page 59 and 60: v) Blinding slab V b0.10.6mLdV b =
Page 61 and 62: Cement is also in V e , V us , V b
Page 63 and 64: Number of rings per evaragecolumns.
Page 65: Summary of derived formulas.• V w

KITUI SAND DAMS

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