MANAGING WATER IN SMALL PRAIRIE WATERSHEDS: LAND USE,RUNOFF AND DEPRESSION STORAGE

摘要

In the semi-arid northern prairies the partitioning of snowmelt water and rainfall betweeninfiltration and runoff is highly sensitive to climatic variability and land use. Most of the runoff is stored indepressions within small closed watersheds and rarely or never contributes flow to major rivers. Virtuallyall the infiltrated water is retained in the soil where it supports crops and other vegetation and is thusreturned locally to the atmosphere through evapotranspiration. A small but important portion of theinfiltrated water continues through groundwater flow systems to be discharged to surface water elsewherein the landscape.For water management purposes the depressions and uplands in small closed prairie watersheds shouldbe viewed as one interconnected unit. The two principal types of management options are: a) changes ofland use (e.g. tall stubble, minimum tillage) which affect snow accumulation and infiltration and b) changesof depression storage (e.g. drainage). Both of these are on-going all through the prairies, with significantimplications for the hydrology of wetlands and streams. The hydrology of small prairie watersheds is nowwell enough understood to allow the laying out of some general guidelines for water management.However, the effects of changes of land use on infiltration, particularly for frozen ground, are as yet poorlyunderstood and the hydrological effects of depression storage need improved methods of quantificationand modeling. Climate variability and adaptation to climate change pose an additional challenge to watermanagement.