Earthquakes occur due to increased pore-pressure in adjoining rocks which lowers ir shearing strength resulting in release of tectonic strain. Draining out water from weaker adjoining rocks actually reduces pore pressure.

A reservoir planned, designed and constructed for one purpose is called a single purpose reservoir whereas a reservoir planned and constructed to serve various purposes toger is a multipurpose reservoir. A small storage reservoir constructed within a city water supply system is called distribution reservoir

The ghat area is one where rainfall is 200 cm or more and in non-ghat areas rainfall is less than 200 cm. The formulas are-
For ghat areas, Yield = (0.85P ? 30.48)
For non-ghat areas, Yield = [P (P ? 17.78)] / 254 where P is rainfall in cm.

The cost per unit storage of dam initially decreases reaches to a certain minimum value and n increases when height of dam is increased. This lowest point on curve gives economical height for which cost per unit storage is minimum.

Since retarding reservoir is not always filled much of land below maximum reservoir level will be submerged only temporarily and occasionally. The automatic regulation of outflow depends upon availability of water. The maximum discharging capacity should be equal to maximum safe capacity of channel d/s.

Useful storage can be defined as volume of water stored in a reservoir between minimum pool and normal pool level. Dead storage is water stored in reservoir below minimum pool level. It is not of much use in operation of reservoirs.

Trap efficiency of a storage reservoir is defined as ratio of total sediment deposited in a given period to total sediment inflow in that period. It can be defined as percentage of sediment deposited in reservoir in spite of taking precautionary control measures.

Surcharge storage is uncontrolled storage which is volume of water stored between normal pool level and maximum pool level. It is that portion above crest of dam?s spillway which cannot be regulated.

The monsoon duration factor (m) for a bad year is 0.5 and that of normal year value is 1.2. For a good year, monsoon duration factor is 1.5.

The site should be such that a deep reservoir is formed because of lower land cost per unit of capacity, less evaporation loss, and less possibility of weed growth as compared to shallow ones. The basin should have a narrow opening so that length of dam is minimum.