Streamflow and precipitation data and characteristics of selected storms for four stream basins in West Virginia, 2017-2020

In cooperation with the West Virginia Division of Transportation, Department of Highways (WVDOH), precipitation and streamflow were measured at four streamgages in West Virginia to compute time of concentration (Tc) and compare it to Tc estimates made using accepted methods. Precipitation and streamflow data were collected during 2017-2020. Storms were identified and classified through an iterative process relying heavily on inspection of graphs. Three hydrograph time metrics that represent Tc were computed for this study: time to rise, time to recede from a high point on the hydrograph to an inflection on the recession, and the time between an inflection on the hyetograph and an inflection on the recession of the hydrograph (PI-to-RI). Seven-minute running averages were used to compute time metrics for the sites with flow data collected at 1-minute intervals. Storms were designated as beginning when precipitation began. A new storm was designated if six or more hours had passed since the previous rain. Periods of intermittent rain were classified as part of the same storm if breaks were less than six hours. Inspection of graphs confirmed that for all sites and storms, a six-hour break in precipitation was enough time for stormflows to end. Subsequent periods were included in the previous storm until another storm began or until flows reached zero. Cumulative total precipitation was computed for each storm. Storms that did not result in measurable flow were identified and excluded from further analysis. This process through this step resulted in the identification of 529 storms. Storms were then ranked by peak flow. The storms with the smallest peaks and therefore the least relevance for design were discarded. The 50 biggest storms from each site were retained for analysis. Three types of hydrograph time metrics were delineated: time to rise, time to recede, and PI-to-RI. To be counted, the rise needed to be (1) at a steady rate, (2) clearly the result of a specific spate of rain, (3) visually distinct, and (4) representative of a meaningful change in flow magnitude. Time to recede was assessed similarly, with the additional constraint that when repeated or sustained rain fell during the recession and caused flow to rise, the event was excluded. The time between PI-to-RI was determined as the difference between a (1) final inflection on the hyetograph before a visually distinct storm peak and (2) the inflection on the receding limb of the hydrograph from a steep decrease in stormflow to a part of the hydrograph with a flatter slope. Hydrograph events were included in analyses if (1) their maximum values were above the flow threshold for the site, (2) the event was not affected by snow, (3) the slope of the rise or recession was consistent and steady during a relevant part of an event, (4) the flow record during the hydrograph event was complete without estimated values, (5) the event in question represented a meaningful change in flow, (6) for recessions, rain that continued while flow receded was minimal and did not appear to interrupt the recession with secondary rises in flow, and (7) whether changes between successive unit flow measurements during the hydrograph event were primarily either increases or decreases, indicating it was primarily stormflow, or largely stable, which characterized minor rises and recessions that exceeded flow thresholds only because they began when baseflow was already high. Quality-assurance metrics were developed and computed to show how well the hydrograph time metrics met these criteria; these metrics are included in this data release.