Despite the recognizable impacts urbanization has on stream morphology and flow patterns, there are many challenges when it comes to accurately predicting and quantifying these impacts. This is especially true for non-perennial streams in semi-arid rangelands. Non-perennial streams tend to lack complete records for streamflow presence and absence. Quantifying how stream channels change in developing landscapes can be problematic without a historical pre-development baseline to compare to. This project focuses on a non-perennial stream channel in West Stroh Gulch, located in Parker, Colorado, an area south of Denver, U.S.A. West Stroh Gulch is a semi-arid rangeland slated to undergo housing development within the next few years. Stream presence and absence is recorded at multiple locations along the stream network with time-lapse photography. Recorded precipitation events and corresponding photos are reviewed to quantify what storm intensities and cumulative depths do, or do not, trigger a flow response. Additional visual observations including soil moisture, standing water, and snow cover are recorded. After more than two years of field camera monitoring, one precipitation event with a total depth of 92-mm and maximum 60-minute intensity of 50-mm per hour triggered streamflow in the channel. In comparison, there were 79 other rain events with depths ranging from 1-mm to 44-mm and intensities from 1-mm per hour to 34-mm per hour that did not lead to flow. Time-lapse observations will continue through the stages of development to capture future stream channel responses to precipitation events and a changing landscape. In addition to continuing time-lapse photography observations, a hydraulic model of the watershed will be built. Topographic pre-development data collected with drone flyovers is used to construct a DEM (Digital Elevation Model) surface of the watershed. This pre-development DEM surface will be combined with SWMM generated post-development flows in the hydraulic model to predict post-development changes to the channel morphology. Model predictions can be compared with actual channel changes over time. Combining model predictions with ongoing observations will create a valuable case study of predicting pre to post development changes in a semi-arid rangeland’s non-perennial stream.
Graduate student Civil Engineering, Colorado State University