VARIATIONS IN TURBIDITY AND FECAL COLIFORM BACTERIA LEVELS IN THE TALLAPOOSA RIVER, HARALSON COUNTY, GEORGIA: ROLE OF BASE FLOW, RISING STREAM FLOW, PEAK STREAM FLOW, WET FLOW AND FALLING STREAM FLOW

The Tallapoosa River heads in rapidly developing Paulding County, flows across more rural Haralson County, and then into Alabama. This section of the Tallapoosa River is the last free flowing section and is recognized as relatively good for fish and invertebrate habitat and as a drinking water supply. Since 1999, American Rivers has on three occasions named the Tallapoosa River as one of the ten most threatened rivers in America. Problems occur because of poor management of the dams in Alabama and rapid development of the headwaters in Paulding County, Georgia. Additionally, an off-line 2300 acre drinking water reservoir that would pump water from the Tallapoosa River has been proposed for Haralson County.

Beginning on 7-7-2005, we have measured turbidity at one site upstream of the proposed reservoir in Haralson County. During some rainfall events measurements are made at 12-hour intervals. Results of 347 turbidity measurements (min = 5.2 NTU, 50 percentile = 10 NTU, and max = 180 NTU) show correlation with flow (r2 = 0.51). Using just daily data the correlation drops to 0.39. Applying the flow characteristics from Hollabaugh and Harris (2004) to rainfall events (base flow, rising stream flow, peak stream flow, wet flow, and falling stream flow) allows further interpretation of the data. Eighty percent of maximum turbidity occurs during the rising stream flow as sediment is washed into the river. Lower turbidity during peak stream flow is possibly the result of dilution. Multiple rain events cause wet flow conditions during which additional rainfall does not greatly increase turbidity, though levels are somewhat elevated. Final results for a flow versus turbidity diagram for the Tallapoosa River show two trend lines. One trend line of low slope includes the rising stream flow stage and the highest turbidity. The second line of much higher slope includes the rest of the data. Traditional definitions of wet and dry sampling events (0.3 inches of rain in 48 hours of the sampling event [Georgia EPD] or 48-hour dry antecedent period followed by at least 0.3 inches of rain in a six hour period [Ohio River Valley Water Sanitation Commission]) or 72-hour dry antecedent period) are in need of updating. Limited fecal coliform bacteria (35 measurements starting in 2006) minimum, median, and maximum results are <10, 160, and 23,000 colonies/100ml.