C150094 Red Mesa Aquifer Groundwater Study 2002

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Red Mesa Aquifer Groundwater Study — Interim Report 2002 The general direction of groundwater flow is from northeast to southwest. Groundwater discharges either directly to the La Plata River or to Long Hollow and its associated draws, and then to the La Plata River. At the northern end of the study an outcrop of Cliff House Sandstone protrudes to the surface. No terrace gravels exist in this area east of Breen. The water table is effectively bifurcated in this area by impermeable sandstone bedrock. This is illustrated with a break of the groundwater contours near the outcrop. The water table contours represent the elevation of the water table. Contours that are more closely spaced represent a steeper water table surface, and vice versa. The May 2001 water table map shows more variations than the December 2001 map with regard to gradients and water table peaks and troughs. These variables are believed to be a response to deep infiltration of ditch seepage and irrigation water. When recharged, the water table is modified. The response is groundwater movement. Six months after the peak irrigation in May 2001, the December 2001 map shows a more uniform water table; there is less variability in groundwater gradients and fewer groundwater mounds and troughs. The elevation, gradient and shape of the water table in the terrace gravel aquifer is affected by recharge from irrigation practices. Similarly, water placed in recharge basins on Red Mesa could be used to change the character of the water table and increase base flows in Long Hollow. A groundwater divide is drawn on each map that is roughly coincident to Highway 140. The groundwater divides were based on the water table contours drawn from well data and describe the drainage to which groundwater would be reintroduced as surface water. Substantially more area of the aquifer flows to Long Hollow and its tributaries than to the La Plata River. During site visits for data collection, flows in Long Hollow tributaries were visually estimated. Flows were observed year round in Mooney Draw, Church Hollow, Spring Hollow and Third Canyon. Consistent flows in Long Hollow tributaries are evidence that groundwater inflows influence flow in Long Hollow throughout the year. 991-077/031 Wright Water Engineers, Inc. Page 9 Interim Report