Original:Rural Water Supply in Nepal (Hydrology-Water Cycle Course)
coua Technical Training Manual No. 1 Publish,?d by: Remote Area and Local Development Department, His Majesty’s Government of Nepal/ Swiss Association for Technical Assistance/ United Nations Children's Fund Kathmandu Nepal Available from: United Nations Children's Fund P.O. Box 1187 Kathmandu Nepal Reproduced by permission of UNICEF/Nepal. Reproduction of this microfiche document in any form is subject to the same restrictions as those of the original document.
Prepared And PAbZished By @mote Area And Local DsveZopment Department, HMG SATA - Swiss Association For Technical Assistiance UNICEF - United Nations Children's Fund Kathmandu 1977
HYDROLOGY - WATER CYCLE COURSE l- Dgfinition Byd:rology is the science of distribution and behaviour of water in nature* Hydrology is a part of climatology. The cycle of water (hydrologic cycle) is without beginning and end and consists of the following: Precipitation , All water from the atmosphere deposited on the surface of the earth as either rain, snow, hail or mist. Surface run off The water which is derived directly from precipitation and passes over ground into water courseso It ,is the precipitation less the losses from infiltration and evaporation. Evaporation, transpiration Combined loss of-water from land and water-surfnce by evaporation and vegetation transpiration. Percolation ,The term percolation describes the passage of water into9 through and out of the ground. Infiltration is the entrance of the water into the ground and its vertical movement down to the ground water table,, while percolation (or ground water flow) is applied to the movement of vater after it has reached the ground water table,
2, Climate Concerning the year, the mai': climatic features in Nepal, Gandaki Zone, are as follows: - The raining seas& of the year, from,April to September (monsoon) . The dry season of the y3ar, from October to April. 7 49 QuanUty and variation of rainfall. in Gandaki Zone, Nepal Iiainfall quanflties can be mapped as for example the following diagram for Pokhara town rainfall in 1975; The: rainfall varies greatly throughout the year and also from one year to the other as well ao from one station to another,
4. Rainfall, run off and infiltration The quantity of water running f+om an area into streams and finally into the sea is not the same as the rainfall. The quantity of rsinfall will be shared into: - direct evaporation - transpiration through vegetation - infiltration - run off Infiltrated water It forms the ground water and through its natural filtration it can be used directly as drinking water, only as far as protective, measurements for catchment sre hdoDtedo The characteristics of the yield of a spring depend on the type of soil and sub-soil,, From rocky area the <quantity of water will directly depend upon the rainfall. Surface springs will also dry up.shortly after the monsoon and supply again after the first rains. Springs from deep porous and water-holding covers, or from far distant catchment areas, are more regular# but their lowest supply quantity does not correspond with the lowest rainfall* Run off Similar characteristics can be found in streams. Rocky areas provide flood and low water according to the rains. Porous and water-holding soils supply the streams with underground water and the quantity may 'still d&crease after the first rains. Quanf;ity of water may also varies because of the snow when the melting time arises.
Important lakes in Gandaki Zone In Pokhara is tire Pewa lake which is partly used fcr hydra-electric purpose with the help of a dam at the lake outlet. Ngar Pokhara there are also two lakes : Begnas lake - Rupa lake In the north - west of Manang district is located the '2%lchi lake
6, Water source8 JO I 6.1 Importance of water The water is very essential for : - life - health and sanitation - as raw material for food production - farming - cattle I The water conservation and the sanitation are importaat to everyone9 6.2 Ground-water 2. The ground-water ie the water which by percolating through the ground reaches the, ground water tablea The quality of the ground-water depends OA: a) The thickness of the stratum which oovers the watebearing soil, this is Important because of lndlreat contaminations like waete water, latrines and fertiliaese, etc... ’ b) The poroeity of the sub-eoi& whioh influsnoee the natural filtration pro0e8se~ The quantify of ground - water depends OA I ‘a) The intake area& It is important to realieo that the - topographloal basin does not nroessarily correspond with the geological or hydrologioal dx8ainage are8o b) 4 d ~m-1 rainfall percolation. This depends on the nature of the intake are%, (kind of vegetation like forest, fa+m, bueh, 97ass fW,d, eta..) Perviousness of tile gro~dr T’ni~ depends on the kind of ma.terie.1, stratification and its homogenety, Storage capacity-of the ground. This depends on the same factors as perviousness and the intake area. 6.3 Springs ff ground-water leaves the ground without artificial help, we call it spring-water. Spring - water is usually the best water quality . Whenever a water supply is planned, first investigation should be made with possibility to pee a spring. The quality and the quantity of the sprirlg depends ens a) Intake area b) Annual rainfall percolation - 12 - continuous flow of a 2prind depends on the following points : a) Thickness of the stratum cover3 Perviousness of the ground c> Storage capability of the ground Example of a srrina influence bv a single rain-trallz Thin snr 5ng - * Y ~ ~~-~ - -v _ not have a constant flow: U- - .___ ------ ‘=- w - A thin stratum covers the water bearing soil - The saturated stratum has a great perviousness (cracks and - The water - bearing soil has little storage capability (few pores which could be filled with water) Examnle of a spring influenced onlv bv annual rainfall. This ' will have a good continuous flow volume : - A thick stratum covers the water - bearing soil - The saturated stratum has a small perviousness. fissure spring ‘8) - - The water - bearing soil has a big storage capability - 13 - . Variation of ground water table and posi tiron of springs according to seaeon . Legend : Saturated stratum Eil o” l P- Clays --a- Wet season water table -x- DV sea8on water table Remarks : Impermeable stratum SPRING 1 : SPRING 2 : SPRING 3 : wet season = large flow Dry season t small Flaw Wet Dry wet Dry season 6eason season season normal flow dry ( no water ) normal flow normal flow - 14 - VARIQUS TYPE OF SPR INGS ~ Type 1. Type 2 . SPRING Under water ~ --. I during wet season , Legend : Impsrmeable stratum Saturated stratum -x- Ground water table Type 3. LEGEND : Impermeable stratum Saturated s.tratum ITsq Pervious stratum -x- Ground wstor table 5,4 Wells A well is a round hole dug in the ground up to a certain distance in the saturated stratum. Wells make it possible to use the underground water for economic applications as for water suppliei or irrigation purposes0 The quality of the water obtained from a well depends on : a) The thickness of the stratum which covers the water - bearing soil. b) The porosity of the sub-soil, . The quar_tity of water obtainable from a well depends on : a) The intake area I b) The annual rainfall percolation c) The perviousness of the ground d) The storage capability of the grounda The different types of wells are as follows: 4 b) The shallow well which draws the water from the permeable stratum between surfaae and the first impermeable stratum, The deep well which draws the water from a deep saturated stratum unaffected by surface impurities. The artesian well which has the similar characteristics as the deep wellerdept that It taps water under pressure which will bring the water to the surface under its own heads TYPE OF WELLS. a = shallow well b deep well - C = artesian well i i Legend : py Impermeable stratum c‘ ..r.r**.: ) -: ; *.' 5 . Smturated rtratum Pervious stratum -x- Ground water fable - 18 - 6.5 Rivers The run-off water or stream -flow is the water which is gathered into rivulets, brooks, streams or rivers, The volume and variation of run-off are influenced chiefly by the rainfall and its distribution by the size, shape, cover and general topography of the \ . catchment area, by the nature and condition of the ground. The melting of the snow also influneces the flow of rivers. For drinking purpose, the water of rivers should be treated by sedimentation and filtratioao Chemical products, (chlorination) can be added for elimination of bacteria. It will be the same for lake water@