Monitoring Changing Lag Time and Flow Duration at a Developing Site in Parker, Colorado
Urban development can have a large impact on watershed hydrology as pervious surfaces are replaced by impervious surfaces. This can cause noticeable changes in runoff and the shape of a watershed hydrograph in response to storm events. We are monitoring West Stroh Gulch, a 0.6 mi2 watershed in Parker, CO, as it develops into residential housing. As construction has progressed, we have observed decreasing lag time and increasing flow duration.Ìý
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To track these changes, we are using precipitation data obtained from Gauge-Adjusted Radar Rainfall (GARR) data and time series flow data from a streamgauge on site, paired with photographs from flow-monitoring cameras set up along the watershed. Generally, the lag times have decreased over time. The average in 2023, when development activities began, was 5.72 hours. Comparatively, the average lag time in 2025 was 2.18 hours, after the main stormwater infrastructure was installed and connected. ÌýFurthermore, the flow duration has increased from an average of 5.88 hours in 2023 to 24.13 hours in 2025. This monitoring will be continued through post-development of the site in order to identify changes in watershed hydrology, and its response to rain events.