OTHER SOURCES OF GROUND WATER
Besides different types of wells following may also sometimes becomes source of water for irrigation.
- Infiltration galleries
1. Infiltration Galleries.
- They are horizontal or nearly horizontal tunnels which are construct through water bearing strata along the river banks to collect the inflow of ground water from river.
- They are also know horizontal wells.
- The galleries are made of bricks, or stones.
- The galleries are laid at some longitudinal slope so that the water collect in the gallery is led out of gallery under gravity flow.
- Galleries are provid with man holes for inspection and maintenance.
- Infiltration galleries are not use for getting water for irrigation purposes.
- When ground water automatically comes to the surface and starts flowing it is call a spring.
- Springs are found in hills.
- They also supply very little quantity of water and as such are not adopt for irrigation purposes.
- Springs may be class into following three types:
(a) Artesian springs
(b) Gravity or shallow springs
(c) Surface springs.
- In the case of artesian springs underground water comes to the surface under hydraulic pressure.
- This spring is form when an aquifer lying under an impervious layer gets punctur or some how fissur.
- Gravity spring develops when ground water table gets exposed due to ups and downs in the surface.
- Surface spring is developed when an impervious stratum which is supporting the ground water reservoirs is out cropped.
- Formation of various springs is given in Fig. 8.22.
- In it a tunnel laid along the hill side to tap water from under ground springs.
- The tunnel has some longitudinal slope.
- As it lies in hard stratum it is
- usually not line
- . Water from Karez is led into an open channel at its down stream end and used as deemed suitable.
- Such tunnels are existing in Baluchistan and North West frontier in Pakistan.