Study of sustaining groundwater resources through percolation ponds during droughts in India

The vagaries of climate change are already being felt in many countries including India. Droughts and floods have perhaps become more common. The time series of rainfall data for c. 100 years in a semi-arid region of India shows (Fig. 1) that every fourth year is a drought year and every seventh year is a year of surplus water causing floods. Thus it becomes imperative for a country like India, situated in the monsoon region (other monsoon countries include Korea, Philippines, China, Japan, Bangladesh, Pakistan, Sri Lanka, Malaysia) to develop adaptive measures to counter the climate changes.

Percolation ponds as artificial recharge structures

A percolation pond or tank is an artificial recharge structure constructed across a monsoon stream with the purpose of harvesting surface runoff caused during the monsoon period. These structures are simple earthen dams to impound surface runoff (Fig. 2a). Generally these earthen dams are a few hundred metres long and a few metres high. Typically the water area for such ponds is less than one square kilometre and storage capacity is less than half a million cubic metres. Due to evaporation losses, only a certain fraction of impounded water (defined as the percolation efficiency) is expected to percolate through the pond bed to the ground-water. The efficiency of such structures is expected to be governed by factors such as geology, climate, rate of silting, age of tank etc. The purpose of this investigation was to determine how effective these structures are and how various governing factors control the efficiency of these structures. Although there are a very large number of such structures in hard rock areas of peninsular India and a huge investment is made in such structures, there are only a few scientific studies.

A qualitative change in the study of such structures was made as a new method was developed to estimate their efficiency based on the chloride balance (Sukhija et al. 1997). This method, in contrast to the conventional water balance method, overcomes the problem of estimating evaporation from the surface reservoir, which is either estimated

Average rainfall (758 mm)

Drought year (every 4th year on average)

Surplus year (every 7th year on average)

1500 1300

1 900

1500 1300

1 900

ft T f

tf* T tl

i , î i Tir

11 ni i i tu u*\

L hi uní k ■ mi v Mpv » ^ y î 11 /. v r

M vi i !

M win1

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

Fig. 1. Rainfall pattern in Nalgonda district (Andhra Pradesh, India) for the last 100 years (1901-1996) showing drought every fourth year and excess rainfall in every seventh year.

PERCOLATION TANK

PERCOLATION TANK

1. At time T1 EVAPORATION

M°nsoon Streaifl

1. At time T1 EVAPORATION

M°nsoon Streaifl

Schematic diagram of a percolation tank

PERCOLATION (not to scale) At time T, Chloride in the Tank = V1C1

Scale to measure the water level

Schematic diagram of a percolation tank

PERCOLATION (not to scale) At time T, Chloride in the Tank = V1C1

2. At time T2 EVAPORATION = f(V, - V2) [Chloride = 0]

0 0

Post a comment