Assessing the Drivers to Understand Changing  Recharge Dynamics in the San Luis Valley, CO

This study aims to develop a method for analyzing groundwater recharge processes by combining water level, pumping, diversion, InSAR, and snow parameters derived from a physically based snow distribution model, along with geochemical data, to reduce uncertainty and reveal recharge dynamics in the SLV. We will also assess the time delay between snowmelt and groundwater response in our study. The objectives of this study are to:

• Examine valley-wide recharge variation due to snowpack changes, snowmelt timing, and rate using gridded model outputs, SNOTEL sites, and SNODAS data products.

• Assess the time delay between valley-wide groundwater recharge and snowmelt.

Assessing groundwater storage loss and aquifer properties in San Luis Valley, CO utilizing in-situ and satellite data

Sustainable groundwater management requires accurate tools to assess changes in aquifer storage as climate extremes intensify and water demand grows. Currently, inadequate in-situ data and uncertainty in storativity estimates limit such assessments. We address these challenges by integrating in-situ observations with Interferometric Synthetic Aperture Radar (InSAR) to estimate aquifer properties and groundwater storage change in Colorado’s San Luis Valley. We estimate storativity for management subdistricts based on the relationship between pumping and water levels, comparing a constant net inflow assumption against a refined time-varying net inflow regression that incorporates climate drivers. Both approaches yield consistent results across diverse hydrogeological settings, producing storativity estimates ranging from 0.03 in primarily confined aquifers to 0.21 in unconfined aquifers. Our results reveal a declining trend in groundwater storage, with a total storage loss of 6.3×108 m³ from coarse-grained layers for our studied subdistricts from 2010 to 2023, driven primarily by drought conditions. We further quantified the partitioning of storage loss, finding that in regions with significant pumping from confined aquifers, inelastic compaction accounts for a much higher portion of the total water withdrawn (39%) compared to regions where pumping is mainly from the unconfined aquifer (9%). In that case, gravity drainage is the dominant mechanism. Conversely, confined aquifers with no long-term depletion show elastic deformation patterns, with no storage loss in fine-grained units. This research offers a transferable framework for assessing groundwater storage loss and prospects for sustainability in data-limited regions and supports adaptive management in water-stressed basins worldwide. 

Quantifying urban water sources from city streams in the Denver metropolitan area from water stable isotopes analysis

Urban streams in the Denver, Colorado, USA region flow more often than undeveloped grassland streams. We sought to identify the sources of this increased flow using water stable isotope data and an analysis of streamflow responses to rain events. We collected and assessed 402 urban stream, 522 tap, and 38 precipitation samples across 2019, 2021, and 2022. Two endmember mixing analysis was utilized to obtain the percentage of precipitation-derived groundwater and tap water contributing to urban baseflow. Our endmember mixing results revealed that a major portion of stream water came from tap water, through excess lawn irrigation returning to the stream and leaking water pipes. The average portions of streamflow that come from tap water and lawn irrigation return flow were 76% and 47% respectively across 2019, 2021, and 2022. Uncertainty related to estimation of tap contribution and lawn irrigation return flow ranged from 3 – 29%. We also observed an increasing correlation between lawn irrigation return flow in urban streams and imperviousness of the watersheds in the Denver area. In semi-arid and arid cities in the USA, including in Denver, urban irrigation consumes a large portion of city water. Through an analysis of spatiotemporal variations in streamflow, we observed that tap water is a larger contributor to urban streamflow than increased stormflow during most months. The joint contributions of tap water and directly-connected impervious area driving increased stormwater lead to profound alterations in the urban streamflow regime compared to grassland streamflow. This study provides insights into how urban irrigation and stormwater together increase streamflow, aiding water managers in implementing effective water management strategies in water-scarce cities.