Question

What are the necessary conditions for sea water intrusion into aquifer? What are the different types of open wells and explain the construction of open well with impervious lining?

Answer 1

8.1Introduction

Water well is a hole or shaft, usually vertical, excavated into the earth for bringing groundwater to the surface (Todd, 1980). Wells also serve other purposes such as for observation/exploration, artificial recharge and disposal of wastewaters (very restricted these days due to environmental concern). Wells of horizontal extent (known as ‘horizontal wells’) are sometimes constructed because of special groundwater situations. Horizontal wells are advantageous in the situation where groundwater is to be derived primarily from infiltration of streamflow (e.g., collector wells) or in the situations where aquifers are thin, poorly permeable or underlain by permafrost or saline water (e.g., infiltration galleries, and small-diameter perforated pipes drilled into hillsides). Interested readers are referred to Todd (1980), Raghunath (2007), Michael et al. (2008) and Sarma (2009) for the details about different types of horizontal wells.

This lesson deal with various functions of wells, classification of water wells, advantages and disadvantages of open wells and tubewells/borewells, and the selection of sites for well drilling and type of well.

8.2 Functions of Wells

Wells are used for a variety of purposes, which are as follows:

(1) To supply water to meet domestic, municipal, industrial and agricultural requirements.

(2) To control seawater intrusion.

(3) To remove contaminated water from a polluted aquifer.

(4) To lower water table for construction projects.

(5) To relieve pressure under dams.

(6) To drain agricultural land or urban land.

(7) To inject surface water or once used groundwater into the ground for augmenting groundwater resources. That is, to artificially recharge aquifers at rates greater than the natural recharge.

(8) To dispose of wastewater or hazardous wastes into isolated aquifers. This function of wells is highly restricted these days due to its detrimental effects on environment.