LOW COST METHODS TO DEVELOP RATING CURVES IN A SMALL IOWA WATERSHED

Dry Run Creek is a watershed under high pressure from its surrounding community with its headwaters located in farm fields and urban drainage ditches. It is subject to flash flooding and erosion and is on the DNR’s list of impaired waters. Various low cost methods are examined to measure discharge that could be duplicated in other small watersheds. A rating curve is developed on 11 sites around the watershed to allow future studies to more easily assess discharge. The average velocity at most sites ranges from .2 to .4 m/s with an average discharge of 0.1 m³/s (3.5 cfs). Many methods face challenges varying from unstable stream banks causing fluctuations in sediment deposits to bent gauges caused by debris from flash flooding. In one site it is difficult to get into the stream and is being measured from a bridge. In some sites depth s are measured by painting gauges on existing structures. Other difficulties occur where the stream is too wide and deep during high flows. Nutrient loading is a concern because larger studies have shown that a significant amount of the nutrients causing hypoxia in the Gulf of Mexico have come from Eastern Iowa. Methods demonstrated in this study could be utilized to perform more studies on small watersheds and understand their role in the nutrients being loaded into the Cedar River and possibly identify areas that are higher contributors and begin to assess ways to remediate.