| OCR Text |
Show PART VIII TECHNOLOGICAL ADVANCEMENTS Harvesting of trees in the spruce-fir, lodgepole pine, white fir- Douglas fir, or aspen vegetation types can result in increased stream- flow. Research in the snowpack zone of the commercial timber types has shown that specially designed timber harvest practices can increase water yields from the area treated by significant amounts. These practices, which modify snow accumulation patterns and snowmelt rates, reduce evaporation losses and prolong the snowmelt period. Thus, more of the precipitation is available for streamflow and at a time when it is most needed downstream. Specially designed timber harvest practices can be complementary to weather modification projects by causing more efficient use of the increased precipitation. Without any specially designed treatment, much of the precipitation in the snow zone returns to the atmosphere through evapotranspiration. Similar opportunities for water yield improvement through vegetation management exist in many areas of noncommercial forest and in brush lands in the Upper Colorado Region. However, the potentials and limitations of each area much be carefully considered. For example, studies in the pinon-juniper vegetation type indicate that type conversion by removal of the pinon-juniper overstory and establish- ment of a range grass-type does not increase streamflow measurably. Due to a combination of factors including limited precipitation, soil characteristics and-associated water-holding capacities, plant rooting depths, and high potential evapotranspiration, the replacement vegeta- tion uses as much water as the pinon-juniper. The principal benefit of such treatment is to utilize available water to better meet the needs of man. Under certain circumstances, mechanical treatment and revegetation of severely depleted watersheds may result in some decrease in total streamflow due to the reestablishment of riparian vegetation along stabilized stream channels and to the stabilization of revegetation of adjacent slopes. The primary benefits of this activity are the decrease in soil loss and attendant debris and sediment and the modification of extreme high and low water flows. Any reduction in streamflow has to be regarded as the cost, in water, of protection from floods and sedi- mentation, stabilization of age-old soil and of stream channels, increased range forage, improved wildlife habitat, and protection of fishery and recreation values along the stream. Snow management in the alpine zone as an operational tool offers promise for improving timing of water yields. Research is actively being pursued in the Rocky Mountains to develop methods for controlling snow accumulation and snowmelt. Current techniques involve installa- tion of snow fences, avalanche control, and application of materials to retard evaporation and control rate of snowmelt. 37 |
