USING TOTAL SUSPENDED SEDIMENT DATA TO EVALUATE THE IMPACTS OF STORM WATER DIVERSION TO A CONSTRUCTED WETLAND AT GRAND VALLEY STATE UNIVERSITY, ALLENDALE, MICHIGAN

Grand Valley State University (GVSU), a mid-size liberal arts university located in western Michigan, was founded in 1960. Over the last fifty years, the Allendale campus of GVSU has expanded by adding over 120 acres of new buildings, walkways, and parking lots. Storm water runoff from these impermeable surfaces was channeled into a series of ravines and has resulted in erosion, slope instability, and sediment discharge into the Grand River and eventually Lake Michigan.

In 2007 GVSU formed the Storm Water Advisory Group (SWAG) comprised of students, faculty, consultants, and facilities managers to develop runoff reduction strategies. In June, 2011 construction of a new library began on the Allendale campus of GVSU. As part of this project approximately eighty percent of the storm water from Little Mac Ravine will be redirected to a new wetland west of campus. Little Mac Ravine is a second order stream with a bankfull discharge of approximately 7.1 to 8.5 m³/s.

Five hundred milliliter water samples from over 10 storm events have been collected prior to storm water diversion using a 6712 Isco automated water sampler triggered by a piezometric water level measurement device. Samples were collected at five minute intervals when the water level exceeded ten centimeters above base level. Twenty five milliliter subsamples were analyzed for total suspended solids (TSS) and volatile suspended solids (VSS) using a modification of the Environmental Sciences Section (ESS) method 340.2. Turbidity, specific conductivity, pH, and salinity were measured in the lab using hand held instruments.

Once water has been diverted from the Little Mac Ravine to the wetland in July, 2011, samples will continue to be collected to quantify the change in TSS. TSS data will be combined with historic and modern flow data to develop a TSS rating curve for pre- and post-diversion flow regimes, and estimate sediment load reduction resulting from the diversion. Preliminary results suggest moderate to low flow conditions typically have TSS values less than 1.0 mg/L. During a flood event June 21, 2011, that exceeded bankfull, TSS values were as high as 6.7 mg/L and remained greater than 3.0 mg/L over a 60 minute period.