Irrigation water pricing policies to reduce and finance subsurface drainage disposal

Abstract

Disposal of water collected in agricultural subsurface drainage systems has normally been done without direct charge to the farmer. In some cases, drainage water disposal costs are becoming very high so that the institution of incentives for the farmer to reduce drainage volumes and pay for their safe disposal are appropriate. The consequences of various irrigation water pricing policies on optimal irrigation application, profits and drainage volumes were analyzed for cotton grown under three levels of irrigation uniformity. The unregulated case led to applied water and drainage flows that exceeded the economically efficient levels. A direct charge on drainage waters equal to their disposal costs induced economically efficient water application but required a drainage water volume monitoring system. A flat fee on irrigation water could be set to induce an economically efficient water application; but in this case, the revenues generated by the imposition of the extra charge greatly exceeded the costs of disposal. Selection of the flat fee to equalize revenues and treatment costs resulted in excessive irrigation compared to the economically efficient levels. Tiered water pricing, whereby the unit water price is increased as volume increases, is another option. When the seasonal crop evapotranspiration was selected as the level to impose the tiered pricing, the tiered price could be selected to induce economically efficient applications. However, the revenues generated by the tiered price were less than the costs for disposal. Water pricing policies suffer from being sensitive to irrigation uniformity. Investment in irrigation technology to improve irrigation uniformity is justified, and the level of investment increases as the costs for drainage water disposal increase.