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Rainfall and Streamflow Analysis of Depression Losses at the Rocky Flats National Wildlife Refuge

This study is centered around the analysis of rainfall and streamflow data collected from a watershed located within the Rocky Flats National Wildlife Refuge. The data was systematically filtered and cleaned to avoid skewness and potential error. Afterwards, a statistical analysis of the data was conducted which led to the creation of detailed relationships between rainfall and streamflow with the intention of updating historical depression loss values. Mile High Flood District (MHFD) gives up depression loss values of 0.2-0.6 in. for open fields, with a recommended value of 0.4 in. This means that we can expect 0.2-0.6 in. to get temporarily captured in depression storage, preventing it from becoming runoff. Now, when we look at the highest and lowest (non-zero) rainfall depths captured by the closest rain gage, in relative proximity to the watershed, which did not result in a flow event, we see these values are 2.48 in. and 0.04 in., respectively. This is significant because the largest value that did not result in a streamflow event is magnitudes larger than that of the recommended value of 0.4 in, indicating much of the captured rainfall must have been lost elsewhere. The relevance of this analysis is not to be underestimated, as it allows for the understanding of the threshold at which a flow event occurs. Additionally, there were 13 streamflow events in the 5-years’ worth of data that were captured with a delayed start time. Of the 13 events, the average delay time from the first instance of rainfall to the first detection of streamflow was 04:51 [hh:mm] with a standard deviation of 04:26 [hh:mm]. The data was further filtered and any time delay above 300 minutes was removed. This led to only 9 rainfall events that led to streamflow being analyzed. The time delay average and standard deviation of these events was 02:16 [hh:mm] and 01:21 [hh:mm], respectively. The investigation of depression losses in open fields presented a unique opportunity to examine the intricate relationship between rainfall depth and flow events. It was recognized that just before the threshold for flow events was reached, a significant quantity of rainfall was lost in depression storage. Therefore, the rainfall quantity was recorded for these 9 specific instances of delay time. The rainfall depth average and standard deviation are 0.64 in. and 0.50 in., respectively. These values allow for a much clearer comparison between the depression loss values given by MHFD and the data from the observed watershed.