If a1 = 10 and an = an-1 + 1 then find the value of a4.

Saturated thickness is the measure which define the volume of water in an hydrogeologically defined aquifer. The rock bearing the aquifer has pores which are also filled with water contributing to the volume of water in an aquifer. The saturated thickness between 1975 and 1990 are 32.77m and 22.48 respectively, hence there is decrease in 10.29m. Also, the saturated thickness between 1995 and 2010 are 25.08m and 12.27m respectively, so there is decrease in 12.81m.

The decrease in saturated thickness is significant between 1995 and 2010 although the population remain the same over this time as that in 1975 and 1990 this may be due to conservational strategies adapted by the population or because of natural reasons like the aquifer received adequate levels of rainfall to maintain the volume of water, water entered from other sources like river, lakes and pond in maintaining the overall volume of the aquifer. Conservational strategies involves replenishment of waste water for reuse and prevention of excess loss of water.