PERMFILE105974 - Laserfiche WebLink

Home Browse Search

numerous counties (currently I'm working with Park, Lorimer and San Miguel County governments), cities, private non-profit and for profit organizations including water conservation and conservancy districts, gravel mine companies and ski azeas. I have been called to testify as an expert at several U.S. Senate hearings, and in numerous federal, and local court cases. At CSU I teach ripazian ecology, and train scientists in approaches for analyzing complex land and water use changes, just like the Milner gravel mine project. I have read the analysis of potential ground water level changes provided by consultants for the mining company. I was surprised to find that they opinions aze well outside the expected range of responses for the system in question. The reports suggest that although pits will be excavated and dewatered, little or no water table decline under floodplain azeas supporting cottonwoods would occur. This is quite simply unrealistic. Floodplains, especially the Yampa River floodplain, contain thick gravel deposits (hence the site of the gravel mine) that aze freely connected to the river. As river stage rises and falls, ground water levels under the floodplain rise and fall indicating the connectivity of the substrate. Pumping water from a lazge gravel pit will create a large cone of water table depression under the floodplain that could extend considerable distances from the pit. This issue is much too critical for guesses and opinions. Scientists have appropriate tools for analyzing this problem and arriving at realistic predictions. A simple ground water model of this site can be created for predicting the range of water table responses to pit dewatering. I have used models of this sort for a wide range of analyses, and a model can be developed by a ground water expert, such as my colleague Dr. William Sanford in my department (Earth Resources) at Colorado State University, in a matter of days. Model development requires topographic data, data on the hydraulic conductivity of the substrate, and scenarios on the range of water elevations to be produced in the pit. Most of this data exists today. The model will eliminate the guesswork presented in the consultant reports and provide you with a more realistic analysis of potential ground water changes. The second issue is the sensitivity of cottonwoods to water table decline. The literature used in a report by Kelly Coffer, "Response of cottonwoods (Popu/us spp.) to different alluvial water table regimes" is based almost entirely on research by Dr. M;chael Scott and myself. While Mr. Coffer represents some of our research results accurately, his review is not complete and not objective. Cottonwoods are extremely sensitive to water available in the upper portion of the soil profile as well as water table depth. In analyzing potential hydrologic effects on cottonwoods both subjects must be analyzed. If dewatering will keep water tables below the upper 3 feet of soil, these soils will not be wetted during spring runoff as the river rises, and a water source that cottonwoods rely on during the summer will be eliminated. When water tables fall even small distances (1-3 feet in gravel soils) below their deepest roots the second major water supply for trees will be eliminated. If either one of these water sources is eliminated trees will experience severe water stress. By stress I mean dieback of leaves, branches and roots. When cottonwood leaves yellow, indicating their impending death, it is too late to implement floodplain hydrologic 2