ENVIRONMENTAL PROFILE | CHAPTER 3


WATERSHEDS AND STORMWATER


The significant surface waters in Cedar Falls are mostly rivers and streams (Figure 3.3). Major waterways in the planning area include:


• Cedar River • Dry Run Creek • Black Hawk Creek


Past and current land uses have compromised the quality of many of these water- ways, and some are listed as impaired waters for their intended uses. A description of each of these waterways follows.


Cedar River


The Cedar River is 338 miles long in its entirety, originating in southeast Minnesota and flowing southeast to the Iowa River, which discharges to the Mississippi River. The river flows through the northern third of the Cedar Falls planning area (Figure 3.3). The 2010 draft impaired waters document (IADNR 2011) lists this river as impaired at the Cedar Falls impoundment and downstream to La Porte City, at the southeast corner of Black Hawk County. The impaired use is “primary contact recreation” due to elevated bacteria levels. In other rivers that are impaired for bacteria the source has been one or more of the following: confined livestock facilities, wastewater treatment facil- ity discharges, failing individual septic systems, application of manure on cropland,


and wildlife.


Dry Run Creek Dry Run Creek and its several tributaries drain about half of the planning area (Fig- ure 3.4). Several detailed studies have been conducted on Dry Run Creek by the IADNR, Black Hawk SWCD, and the University of Northern Iowa. In brief, Dry Run Creek is classified as a third order, Class B warmwater stream. The mainstem of the creek is 22 miles long, with a total of 50 stream miles when considering all its tribu- taries in the watershed. The entire Dry Run Creek watershed (which extends south- west of the Cedar Falls planning area) is 15,248 acres, with 11,085 acres inside the planning area. Fifty-five percent of the watershed is cropland, with most of this in upper tributaries. Bottom and banks of the stream are scoured, and many urban reaches are armored.


There are 33 inches of rainfall annually in Cedar Falls. In 1850 about 10 percent of the year’s rainfall ran into the stream; the rest evaporated, was taken up by plants, or infiltrated and recharged groundwater (Black Hawk SWCD 2009). Groundwater was slowly discharged to the stream and maintained stream levels between rains. Today, even small storms (<0.5 inches, which occur many times each year) quadruple the flow in Dry Run Creek and raise the stream ¾ foot. In 2002, 22 percent of the entire watershed was urban and 9 percent was impervious. Studies have shown that 20-50 percent more water leaves urban areas when compared with rural areas (IADNR 2010). In downtown Cedar Falls and other high-impervious areas (20-60 percent impervious), up to half the year’s rainfall flows directly into Dry Run Creek rather than infiltrating and recharging the groundwater (Black Hawk SWCD 2009). In addition, much of the


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