Monitoring Techniques

Continuous Water Level Recorders

MCWD uses pressure transducers (aka Level TROLLs) to measure stream stage in stilling wells located next to the streams.  The stream stage or water level is then used to calculate discharge of a stream. There are currently 9 units at various locations within the watershed.  This data is crucial for the calibration of the District's XP-SWMM model.

Stormwater Sampling

In addition to recording continuous stage measurements, at some of the stream locations, the Level TROLLs are connected to equipment that collects stormwater samples.  When the Level TROLLs detect a determined amount increase in stream stage within 30 minutes, equipment is triggered at the end of the storm event, the samples are collected immediately and sent off for analysis (TP and TSS).  The resulting event mean concentration (EMC) is crucial for the calibration of the District's PLOAD model. 

Telemetry

In 2007, the MCWD successfully installed land line phone telemetry at 3 locations along Minnehaha Creek, including the Grays Bay outfall (CMH07), I-494 ramps (CMH19), and the Browndale Dam (CMH03).  The data is transmitted back every 2 hours from Grays Bay and one daily download at I-494 and Browndale Dam to a designated MCWD computer at the office, allowing broadcast of 1) Lake Minnetonka water level, 2) discharge out of the Grays Bay Dam, and 3) discharge out of the Browndale Dam.  In 2013, the land lines will be updated with cellular modems.  The data collected provides  more accurate information for the public regarding discharge levels and recreational safety along the entire length of Minnehaha Creek (in combination with the Web broadcast of discharge at Hiawatha Avenue provided by the USGS).  The information will also be useful in determining the best method to regulate discharges coming out of the Grays Bay Dam for recreational use and prevention of downstream flooding.