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Sunday/Monday Runoff

02 Mar 2023 05:30 AM
Sunday night and into Monday of this week featured a significant rainfall event with a number of locations receiving over an inch of rain. A big question is how much of this rainfall infiltrated the ground vs immediate run off due to frozen soils. You have generally have guessed an answer to this by observing the various nearby rivers running at bankful or not after the event. Anyway, the Daily Erosion Project (an ISU research project closely tied with the IEM) runs a physical model called WEPP that attempts to use real-world inputs to analyze soil erosion on a daily time step. The featured map presents an output from this model system with the plotted ratio between water runoff and precipitation for the two day event. An immediate caveat is that the red area over northern Iowa is likely poorly simulated with model producing too much snow vs rainfall for the event. The rest of the area is extremely interesting with runoff percentages shown at very high values and even above 100% (snowpack being melted) due to frozen soils. There are areas south and east of Des Moines that indicate much of the rainfall did infiltrate due to model analyzing the frost being mostly gone. Areas further south in the red are likely completely frost free and good infiltration did occur.

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