The Shingle Creek and West Mississippi Watershed Management Commissions annually monitor water quality in the lakes and stream of the watersheds. The Commissions’ technical staff obtains most stream water quality data.
Water quality is related to the volume of water flowing to and through the streams draining the watershed and is influenced by the amount of precipitation received and the type of precipitation events. 2006 was a below average precipitation year. The timing of events and rainfall intensity also play a part in determining water quality. This annual variability is why on-going, long-term monitoring is necessary to determine what is an actual trend and what is just natural variation.
The Commissions’ 2006 primary stream monitoring program was conducted in two locations. The 2006 outlet-monitoring site was located on Shingle Creek at 45th Avenue. This site was designated as SC-0 and collects drainage from about 41 square miles, or 92% of the watershed. The upper watershed site was designated Site SC-2 and collects drainage from about 22 square miles, or 50% of the watershed. It was located on Shingle Creek upstream of Zane Avenue near the Brooklyn Park-Brooklyn Center border.
Site SC-1 is located on Shingle Creek at Queen Avenue near the border between Minneapolis and Brooklyn Center. Site SC-1 collects drainage from about 31 square miles, or 70% of the watershed. The United States Geological Survey (USGS) maintains this site as part of the USGS National Water Quality Assessment Program. The Commission and the USGS collected storm event samples at this location up until 1999 when water quality monitoring was discontinued. The USGS continues to monitor flow at this site and monitored for chloride and conductivity in 2006. Flow and other parameters at this site can be monitored real-time at http://waterdata.usgs.gov/mn/nwis/uv?05288705.
The 2007 Water Quality Report
provides more detail on the Commissions’ stream monitoring activites.
Water Quality – Shingle CreekShingle Creek 2-year 3-hour rain event
On August 19, 2009 the northern suburbs in the Shingle Creek watershed experienced a 2-year 3-hour rain event, receiving 1.8 inches in 3 hours. On that day, Brooklyn Park City staff took photos of Shingle Creek at the Village Creek development between Zane and Regent Avenues at the height of the event and Wenck staff took photos a few hours after the event. Since one of the Commission monitoring stations (SC-3) is just upstream of this development and the Crystal Airport rain gauge is nearby, this was a good opportunity to graphically and pictorially demonstrate stream “falshiness.”
One of the major difficulties in managing an urban stream is that they tend to be very responsive to precipitation events. Storm sewers efficiently carry runoff to the stream, which rises rapidly. The engineered shape of modified channels such as Shingle Creek conveys the stormwater rapidly downstream at high velocities. The stream level falls nearly as rapidly as it rose, often with small secondary peaks as stormwater ponds and other storage areas discharge later in the event. When the stream returns to much lower base flow, the engineered channel is usually overwide, and the stream depth can fall to only a few inches.
This “flashiness” can be destabilizing to streambanks. It is also hard on aquatic organisms as they may have few natural refugia left to shelter them from the sudden increased stream flows. Channels are engineered to efficiently carry high flows, and at low flows are very low or even dry. The flashiness of urban runoff is one of the key stressors in most urban stream biotic TMDLs, including Shingle and Bass Creeks.
Figure 1 is a storm event hydrograph that shows streamflow and precipitation starting at about 10:00 a.m. on August 19 through 11:00 p.m. Streamflow was recorded in cubic feet per second (cfs) at 15 minute intervals, and precipitation was recorded in inches per hour. A light rain started falling in the late morning, with about 0.2 inches received in about three hours. Flow started increasing in the Creek almost immediately, and the level logger at SC-3 shows a stream stage increase of about four inches. As the storm grew in intensity, 0.42 inches of rain fell in the first hour (noon-1 p.m.), 0.94 inches in the second hour (1 p.m. – 2 p.m.), and 0.41 inches in the third hour (2 p.m. – 3 p.m.). Streamflow increased from 4.7 cfs to 268 cfs in two hours, and stream stage rose another 3.4 feet. After 3 p.m. the precipitation tapered off and streamflow fell, but stayed at about 20 cfs for the next few days as upstream ponds, wetlands, and other storage areas discharged. Figures 1 - 5