USGS Washington Water Science Center
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Flooding in the lower part of South Prairie Creek, near Tacoma, has increased in recent years, and residents are concerned that increased logging and development in the upper part of the basin may have caused the increased floods. The Pierce County Surface Water Management Utility, which is responsible for alleviating the effects of flooding caused by changes in land use, is interested in determining if there has been a change in the flooding potential in the basin and in estimating the discharge and areal extent of flooding in the lower portion of the basin that can be expected to occur under current conditions. Also, the county is interested in the effects of floods on several design options being considered to reduce erosion and overbank flooding on one stretch of the creek.
To help provide a better understanding of the situation, the USGS is computing the changes in the number of acres developed and clearcut within the watershed over the last two to three decades and determining if there is any concurrent trend in the flooding potential of the basin that cannot be attributed to climatological or hydrological changes. If a trend is found, The USGS will estimate new flood discharges for various flood probabilities and map the areas inundated by the estimated floods, and will determine the effects on design options.