Monitoring Effects of Wildfire Mitigation Treatments on Water Budget Components: A Paired-Basin Study in the Santa Fe River Watershed, New Mexico

Abstract:

A paired basin study in the Upper Santa Fe River watershed following forest restoration measured water budget components in a treated and untreated basin. The paired basin study was established to investigate questions that have arisen with regards to changes in the amount and timing of water yield following forest treatments. Precipitation, stream flow, soil moisture, chloride concentrations in precipitation and stream flow were measured to quantify the water budget components. While the study is ongoing, the results from six water years show a high degree of confidence in the techniques applied. The total inflow from precipitation for each integration period minus the outflow of stream flow, evapotranspiration, recharge and soil moisture leaves a remainder of less than 1%, thus most of the water is accounted for. Volume-weighted chloride concentration in precipitation ranges from 0.20 to 0.23 mg/L for the three integration periods. The annual volume-weighted chloride concentration in stream flow for the same periods ranges from 2.18 to 3.32 mg/L in the treated basin and 0.93 to 1.35 mg/L in the control basin. Based on the ratio of chloride in precipitation to the concentration in stream flow, evapotranspiration is estimated to be about 90 to 96 percent in the treated basin and 76 to 85 percent in the untreated basin for the three integration periods of the ongoing investigation. Higher evapotranspiration rates in the treated basin may be due to the change in vegetation or to a greater area at a lower elevation with a west facing slope. While no increase in stream flow in the treated basin from the forest treatments has been detected, the intensity of runoff appear to be reduced from pre-treatment to post-treatment conditions. With continued monitoring as the vegetation reestablishes to the desired “restored” condition, we will be able to track changes in the water budget.A paired basin study in the Upper Santa Fe River watershed following forest restoration measured water budget components in a treated and untreated basin. The paired basin study was established to investigate questions that have arisen with regards to changes in the amount and timing of water yield following forest treatments. Precipitation, stream flow, soil moisture, chloride concentrations in precipitation and stream flow were measured to quantify the water budget components. While the study is ongoing, the results from six years show a high degree of confidence in the techniques applied. The total inflow from precipitation for each integration period minus the outflow of stream flow, evapotranspiration, recharge and soil moisture leaves a remainder of less than 1%, thus most of the water is accounted for. Volume-weighted chloride concentration in precipitation ranges from 0.20 to 0.23 mg/L for the three integration periods. The annual volume-weighted chloride concentration in stream flow for the same periods ranges from 2.18 to 3.32 mg/L in the treated basin and 0.93 to 1.35 mg/L in the control basin. Based on the ratio of chloride in precipitation to the concentration in stream flow, evapotranspiration is estimated to be about 90 to 96 percent in the treated basin and 76 to 85 percent in the untreated basin for the three integration periods of the ongoing investigation. Higher evapotranspiration rates in the treated basin may be due to the change in vegetation or to a greater area at a lower elevation with a west facing slope. While no increase in stream flow in the treated basin from the forest treatments has been detected, the intensity of runoff appear to be reduced from pre-treatment to post-treatment conditions. With continued monitoring as the vegetation reestablishes to the desired “restored” condition, we will be able to track changes in the water budget.