c. Turbid Water. Water from muddy streams can be improved in quality by
digging intake galleries along the bank. A trench is dug along the bank deep enough so
that water from the stream percolates through the soiI into the trench. The trench is
filled with gravel to prevent the sides from collapsing. The intake strainer is placed in
the gravel below the water line (see figure 6-4). The amount of work required to
construct the gallery is justified by the reduction in the amount of chemicals needed to
quality of the water obtained.
Figure 6-4. Gravel-filled gallery intake.
a. Types of Wells. Because ground water usually has fewer contaminants than
surface water, wells are considered excellent water sources, if the quantity is adequate.
Several types of wells may be used. The type used depends on the nature of the soiI
formations above the water table, the equipment available, and the depth to the water
table. Wells may be of the following types:
(1) Dug wells. Dug wells are the oldest type of well and are stiII found in
abundance in rural areas worldwide where the water table is not so deep as to make
digging impractical. Dug wells are usually excavated by hand; therefore, no tools more
sophisticated than a pick and shovel are required. Since they do not penetrate very far
into the water table because of the difficulties in manual excavation below the water
level, many dug wells faiI in times of drought. They are, therefore, considered relatively