Shoreline-area ratio as a factor in rate of water loss from small sloughs

Abstract

Data collected from 1963 to 1969 at Melfort, Saskatoon and Swift Current, Saskatchewan, have established that rate of water loss from small sloughs varies directly with the length of shoreline per unit area and, therefore, inversely with the size of individual sloughs. This relationship may be caused by lateral seepage to transpiring marginal vegetation, soil evaporation and to groundwater.Maximum daily rate of shoreline-related water loss near Melfort is just over half (0.10 inches) that at Saskatoon and Swift Current (0.18 and 0.17 inches). The daily rate of shoreline-related seepage loss to groundwater is estimated to be 0.02 to 0.04 inches per 1000 ft of shoreline per acre on heavy lacustrine clay at Melfort and double to triple that (0.07 inches) on sandy lacustrine material at Saskatoon and on medium textured glacial till at Swift Current. Therefore, during the growing season up to 60 per cent of the shoreline-related water loss at Saskatoon and Swift Current and 60 to 80 per cent of this loss at Melfort can be attributed to transpiration by marginal phreatophytic vegetation and evaporation from the soil surface.Shoreline-related water loss accounts, on the average, for 60 per cent or more of total water loss in sloughs 0.10 acre or less in size and for not more than 30 to 35 per cent of total loss in sloughs larger than one acre. It is, therefore, a major contributing factor to the rapid drying of all sloughs in the final stages of their existence.The Y-intercept value from the regression of water loss on shoreline per acre provides, for the period from June to September, an estimate of daily lake evaporation. On the average this estimated rate deviates from measured daily lake evaporation by +0.008 inches at Saskatoon and −0.012 inches at Swift Current. Further refinements of this technique should increase its accuracy.