Zhang et al. (2026) Mountain front recharge of a karst aquifer in the Denver Basin, southeastern Wyoming (USA): Recharge mechanism and multiyear drought impacts

Identification

• Journal: Hydrogeology Journal
• Year: 2026
• Date: 2026-03-26
• Authors: Ye Zhang, Christopher A. Akurugu, Noriaki Ohara, Mark E. Stacy
• DOI: 10.1007/s10040-026-03063-w

Research Groups

• Department of Geology & Geophysics, University of Wyoming, Laramie, WY, USA
• Department of Civil & Architectural Engineering & Construction Management, University of Wyoming, Laramie, WY, USA
• Stantec Inc., Fort Collins, CO, USA

Short Summary

This study investigated mountain-front stream recharge mechanisms to a karst aquifer in the Denver Basin, southeastern Wyoming, and the impacts of a multiyear drought (2017–2022) on aquifer water levels. It found that snowmelt-driven streamflow is the primary recharge source via fractures and conduits, and drought significantly reduced aquifer recharge, highlighting the critical reliance on mountain snowmelt.

Objective

• To examine the mountain-front stream recharge mechanisms to a karst aquifer in the Denver Basin, southeastern Wyoming, and to assess the impacts of a multiyear drought (2017–2022) on aquifer recharge and water levels in a context of negligible water use.

Study Configuration

• Spatial Scale: A semi-arid region in the Denver Basin, southeastern Wyoming, USA, specifically the approximately 69 square kilometer Belvoir Ranch, located about 25 kilometers southwest of Cheyenne. The study focuses on three subwatersheds (Lone Tree Creek, Goose Creek, and Duck Creek) at the mountain front, downstream from the Laramie Mountains.
• Temporal Scale: An 8-year period from 2016 to 2023, encompassing a 6-year drought from 2017 to 2022. Data were collected hourly and analyzed on annual and multi-year scales, often using water years (October 1 to September 30).

Methodology and Data

• Models used: Rating curves, Mann–Kendall trend analysis, Seasonal and Trend decomposition using LOESS (STL), Piper diagrams.
• Data sources: Existing geological maps, borehole drilling and logging records, geophysical surveys, and hydrochemical data. New monitoring data included hourly stream depths from six stream gauges, hourly groundwater levels from seven monitoring wells (one new, six existing), and manual water level measurements. Regional precipitation data were obtained from NOAA climate stations and snowmelt/rainfall data from Crow Creek SNOTEL. Hydrochemical data (pH, temperature, electrical conductivity, major ion concentrations) were collected from streams and wells.

Main Results

• In the northern subwatershed (Lone Tree Creek), stream and aquifer water levels exhibited annual cycles driven by spring snowmelt, with stream recharge occurring through fractures and conduits at sinks. Hydrochemical similarities between stream water at sinks and groundwater in wells over 1 kilometer downstream support this mechanism.
• Near-stream groundwater levels responded rapidly (hours) to streamflow peaks, while more distant wells showed a delayed response (1–2 months), indicating spatially variable hydraulic diffusivity and concentrated flow near the stream.
• A 6-year drought (2017–2022) significantly reduced streamflow and led to a mean decline of approximately 3.5 meters per year in aquifer hydraulic heads across all monitored wells. Statistical analyses (Mann–Kendall, STL) confirmed significant declining trends in both streamflow and groundwater levels.
• In the southern subwatersheds (Goose Creek and Duck Creek), recharge to the confined karst aquifer likely originates from a combination of local stream losses and subsurface inflow, potentially from the northern Lone Tree Creek area, supported by hydrochemical similarities.
• Recharge mechanisms for the unconfined aquifer portion could not be definitively determined, and local precipitation was not a significant recharge source.
• Despite above-normal regional precipitation in 2023, below-average mountain precipitation caused continued streamflow and aquifer depletion, emphasizing the critical dependence of the Denver Basin's water supply on mountain snowmelt runoff.

Contributions

• Provides a baseline understanding of natural mountain-front recharge mechanisms and multiyear drought impacts on a karst aquifer in a region with negligible water use, which is crucial for future water management.
• Elucidates the dominant role of snowmelt runoff from the Laramie Mountains in controlling aquifer recharge timing and magnitude.
• Highlights the spatial variability of recharge dynamics within the karst aquifer, influenced by streamflow rates, extent of stream-aquifer intersection, distance to streams, and subsurface permeability heterogeneity.
• Offers insights into the complex interplay of different recharge pathways (MFR, potential MBR, and limited DVR) in a semi-arid mountain-front setting.

Funding

• Groundwater modeling of the Casper Aquifer, Belvoir Ranch, Cheyenne, Wyoming Water Research Program (2015–2018).
• Shallow subsurface monitoring to improve recharge and hydraulic conductivity estimation for the Casper Aquifer, Belvoir Ranch, Cheyenne, Wyoming, USGS (2016–2017).
• Stream and riparian groundwater monitoring to improve recharge estimation for the Casper Aquifer, Belvoir Ranch, Cheyenne, Wyoming, USGS (2017–2018).

Citation

@article{Zhang2026Mountain,
  author = {Zhang, Ye and Akurugu, Christopher A. and Ohara, Noriaki and Stacy, Mark E.},
  title = {Mountain front recharge of a karst aquifer in the Denver Basin, southeastern Wyoming (USA): Recharge mechanism and multiyear drought impacts},
  journal = {Hydrogeology Journal},
  year = {2026},
  doi = {10.1007/s10040-026-03063-w},
  url = {https://doi.org/10.1007/s10040-026-03063-w}
}