A SPATIAL RELATIONSHIP BETWEEN STREAM SLOPE STABILITY AND WATER QUALITY WITHIN AN URBAN WATERSHED IN ROCK ISLAND, IL

The consistently observed phenomenon of highly altered streams and degraded water quality draining urban areas across the U.S is described as the urban stream syndrome. Rock Island, Illinois, contains a population of nearly 39,000 people, and houses industrial and logistical businesses amidst a city of aging infrastructure. Streams occupy ravines that have incised into the Quaternary loess plateau, flowing south towards the Rock River and north or west towards the Mississippi River. In an attempt to understand better the severity of Rock Island’s urban stream syndrome, this project analyzed stream slopes within the Rock Island watershed to categorize their level of instability and differentiate more or less stable sites based on dimensional measurements of the stream, bank angle, etc. Bank stability scores were then compared to hazardous levels of phosphates, chlorides, total suspended solids (TSS), and total dissolved solids (TDS), as well as stream discharge. Definitive results show that all sites within the watershed have TDS, TSS, and phosphate levels well above the maximum contaminant levels set by the EPA while a majority of the sites had safe levels of chlorides. In general, water quality improves with distance downstream. Of the 20 sites studied in this highly urbanized watershed, 9 ranked as having moderate instability while 11 had high instability. TDS, TSS, and chlorides correlated reasonably well, in that high concentrations of each correlated positively with more unstable sites. Phosphates and stream discharge did not present patterns when compared to the stability ratings. Consequently, this rating system requires refinement to better distinguish stream slope stability. This project recommends that the city of Rock Island communicate to residents the importance of mitigation strategies to reduce bank erosion and water pollution. Rock Island and other communities need to work to lower urban pollutants draining into the Mississippi, given the hypoxic conditions and consequent ecological degradation observed downstream and in the Gulf of Mexico. Moreover, healthy urban aquatic ecosystems increase their aesthetic qualities while decreasing their environmental hazards.