Seepage and Evaporation Determination Using a Liquid Level Interferometer (Laser)

Abstract

A liquid level interferometer has been built to measure changes in water level to an accuracy of /8. A novel magnetic suspension is used to position the floating retroreflector of a laser interferometer. Direction sensing is achieved by dual optical channels phased near quadrature by means of an absorbing beamsplitter. The interferometer (laser) has been used to measure very accurately the drop in water level of a lined reservoir. The drop in water level thus provides a precise method of measuring evaporation. It was found that this drop in water level essentially ceased when the relative humidity approached very closely or equaled 100 percent during early morning calm periods. This provides a method of determination of seepage loss. In an unlined reservoir during calm periods when the relative humidity is 100 percent any remaining drop in water level is due to seepage. The laser can measure this rate.