at Coon Creek Hollow, Vale Street , Coon Rapids
STORET SiteID = CoonCreek_CoonHollow

Notes: Coon Creek is a major drainage through central Anoka County. This monitoring location is the closest to the outlet to the Mississippi River that is accessible and does not have backwater effects from the Mississippi during high water. Development in the watershed ranges from only moderately developed areas with one-acre lots to dense urban areas near the monitoring location. The stream is about 30 feet wide and 1.5 to-2 feet deep at the monitoring site during baseflow. Both stream water levels and flow are available for this site.

Coon Creek has flashy responses to storms (see hydrograph on next page). Water levels rise quickly in response to precipitation, but return to baseflow conditions more slowly. The quick, intense response to rainfall is runoff from the urbanized downstream watershed near the monitoring station. The slower return to baseflow is p rob ably due, in large part, to water being release more slowly from the less-developed upstream portions of the watershed. Several example storms serve to illustrate this phenomena. A 1.79inch storm on 6/28/2005 caused water levels to increase 18 inches in the first two hours, and increase another seven inches in the following two hours. The peak water level following this storm was achieved within 4 hours of the first increase in water. It took about 3 days to return to pre-storm water levels. A second example is a 1.47inch storm on 8/26/2005 . Water levels rose 33 inches in the first four hours and peaked only two hours later. It took about 7 days to return to pre-storm water levels. Other larger storms, such as a 3.52 inch rainfall on 9/21/2005 had even more dramatic responses. During that rainfall water levels rose 17.5 inches in the first two hours and peaked after only four hours, but the falling side of this hydrograph was many days long (and prolonged by additional smaller rainfalls). The discussion above is obviously simplified because it neglects to consider the phenology of each of the storms. It only serves to emphasize that this stream responds quickly and dramatically to storms but water levels fall much more slowly.

A rating curve was developed in 2005 so that stream flow estimates can be calculated from the continuous water level record (see next page). A rating curve is the mathematical relationship between water level and flow. This mathematical relationship is determined by taking manual measurements of stream flow during many different water levels. Under extremely high water levels flow measurements could not be safely taken, so the rating curve is only considered accurate for water levels less than 822.0 ft msl (i.e. flows >38.19). In 2005 stream flows ranged from 6.65 cfs to over 38.19 cfs. Given that the maximum water levels in 2005 were 1.26 feet greater than the capacity of the rating curve it is likely that the highest flows in 2005 had flows of >50 cfs.

*Note: Not all monitored years are listed. Please refer to mapping utility for complete data.