This chapter, applicable only to the Coachella Valley Water District, is necessary because of the special and unique problems of imported ground water recharge of ground water basins within such district and the necessity of the payment of part of such expense by a water replenishment assessment. This problem is not common to all districts formed under this division. It is therefore hereby declared that a general law cannot be made applicable and that the enactment of this chapter as a special law is necessary for the solution of problems existing in the Coachella Valley Water District.