Reservoir Pmf Sma Analysis of A Rocky Mountain System – Santa Fe, Nm

The Santa Fe River drains from its headwaters in the Sangre de Cristo Mountains through the McClure and Nichols Reservoir system to the City of Santa Fe, New Mexico. The two-reservoir system is critical infrastructure for municipal water supply and for flood control and attenuation. In consideration of maintenance and stewardship of the reservoirs, and with recently updated Probable Maximum Precipitation (PMP) guidelines, a Probable Maximum Flood (PMF) hydrological analysis of the watershed was performed for maximum inflow assessments. The contributing 22.6 square-mile Santa Fe River watershed can be characterized as mature subalpine forest with rugged and undeveloped terrain. Surficial soil types are rocky, decomposed bedrock with high infiltration rates, overlaying fractured igneous bedrock lenses. Snowmelt runoff is dominant for non-storm hydrology, with groundwater storage and saturation dependent on recent snowpack history. The foothills are subject to convective storms and orographic lifting with common high-intensity, local precipitation events. High infiltration rates, groundwater storage fluctuation with snowmelt, and temporal precipitation distribution may indicate the importance of saturation-excess runoff mechanisms in addition to infiltration-excess runoff. Proposed watershed response models for the PMF included Soil Moisture Accounting (SMA) method within HEC-HMS to account for one component of precipitation losses. Specifically, SMA allows for saturation-excess runoff mechanisms in addition to more traditional infiltration-excess mechanisms with both groundwater storage and transfer to surface flow included. SMA has been proposed by others in applications to mountainous foothill watersheds in the Colorado Front Range, similar in characteristics and processes with the project watershed. These methods are applied to the specific characteristics of the Santa Fe River watershed with calibration parameters tuned to maximum precipitation and runoff events observed over the period of record. An overview is provided of the Santa Fe River watershed, its reservoir system and dam characteristics, the development of SMA model parameters, calibration of the model to local precipitation data, determination of PMP inputs, model results, and sensitivities. Discussion of SMA model performance compared with infiltration-excess methodologies is provided along with lessons learned for this specific case study as they pertain to PMF and PMP model inputs and results in the Southern Rocky Mountain Region.