Final Report: Tidal Creek Monitoring and Reporting ProgramEPA Grant Number: R829322
Title: Tidal Creek Monitoring and Reporting Program
Investigators: Cabiness, Laura , Vaughn, Tracy
Institution: City of Charleston
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 2001 through September 30, 2003
Project Amount: $399,788
RFA: Environmental Monitoring for Public Access and Community Tracking (EMPACT) (2001) RFA Text | Recipients Lists
Research Category: Environmental Statistics , Water , Ecosystems , Air , Ecological Indicators/Assessment/Restoration
The population of the Charleston, South Carolina, area is projected to increase by approximately 15 percent from 2000 to 2020. Planners and government officials in coastal areas are challenged with providing the necessary infrastructure and services to accommodate this growth and, at the same time, avoid increased loadings of point and nonpoint source pollutants to estuarine environments. Estimating pollutant loadings into tidal creeks and determining the impacts on water and sediment quality in the estuarine portion of tidal creeks provide essential information for developing effective stormwater management and remedial action plans. Over a 12-month period, the U.S. Geological Survey and the South Carolina Department of Natural Resources worked cooperatively with the City of Charleston to quantify stormwater runoff from four estuarine watersheds in the Charleston area, characterize stormwater quality from the four watersheds, and compute rainfall-event loadings of selected constituents from the study watersheds. The field and laboratory data provided by this investigation will be useful to the City of Charleston in developing effective stormwater management and remedial actions for nonpoint source pollution.
The four creek watersheds represented different stages of development based on population density. Shem, Bulls, and Parrot Creeks represent urban, high-density residential, and medium-density residential land uses, respectively. Old House Creek served as a reference creek with undeveloped forest and salt marsh representing the predominant land cover. The impervious area of the watersheds ranged from less than one percent to 54 percent in the undeveloped and urban watersheds, respectively.
The three data-collection stations chosen for each creek represent upper, middle, and lower segments of each creek. The U.S. Geological Survey operated the most upstream (headwater) station for each creek, and the South Carolina Department of Natural Resources operated the remaining two stations for each creek. During the 12-month investigation, selected parameters such as water level and precipitation were monitored continuously at the headwater stations. The remaining stations were monitored in conjunction with selected sampling events, which included periods of stormwater runoff and nonrunoff (base flow) conditions. Water samples were collected at each creek to document up to five runoff and two base-flow events. These water samples were analyzed for selected constituents, including total nitrogen, total phosphorus, suspended sediment, and fecal coliform bacteria.
The highest concentrations for total nitrogen and total phosphorus occurred in the spring or summer runoff events. This could be the result of seasonal, residential usage of fertilizer and other chemicals. In general, total suspended-sediment concentrations in stormwater runoff were highly variable, and differences among the four watersheds were not evident. Samples collected during runoff and base flow events from all four watersheds indicated the presence of fecal coliform bacteria. The majority (66 of 87) of the samples analyzed for fecal coliform bacteria exceeded the State contact recreational criterion, and all samples exceeded the State shellfish criterion.
In summary, the following conclusions were developed from this project:
- Pollutant concentrations were higher in creeks with developed watersheds compared to the reference creek.
- Pollutant concentrations were highest at the most upstream site and lowest at the most downstream site. Dilution probably played a large factor in this distribution.
- There were no differences in nutrient and suspended sediment concentrations during rain events and base flow events. The fecal coliform concentrations and biochemical oxygen demand were higher during rain events compared to base flow events. The carbonaceous biochemical oxygen demand had the opposite pattern and was higher during base flow compared to rain events.
- Flushing rates varied among the four creeks and ranged from 3 to 40 days. Pollutants entering the headwaters of Shem Creek stay within the creek for approximately 40 days. In comparison, pollutants entering the headwaters of Bulls, Old House, and Parrot creeks stay within the creeks for approximately 3 to 5 days.
- Stormwater runoff entering developed creeks is faster (hours) than the reference creek (days).
- Pollutant loadings varied depending on the parameter. Ammonia, dissolved nitrate plus nitrite, 5-day biochemical oxygen demand, and carbonaceous biochemical oxygen demand loadings were higher in Bulls and Shem Creeks compared to Parrot and Old House Creeks. In comparison, total nitrogen, total phosphorus, fecal coliforms, and suspended sediments loadings were highest in Bulls and Old House Creeks compared to Parrot and Shem Creeks. Loadings often were high in Old House Creek because of the long return time of rainfall.