Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2005
Publication Date: 12/15/2005
Citation: King, K.W., Harmel, R.D., Fausey, N.R. 2005. Development and sensitivity of a method to select time- and flow-paced storm event sampling intervals. Journal of Soil and Water Conservation. 60(6):323-331. Interpretive Summary: Public awareness and concern about pollutants such as nutrients, pesticides, and sediment entering our streams and lakes has prompted many government entities and action groups to initiate monitoring programs aimed at quantifying the amounts of these pollutants, but there is a lack of guidance for selecting a sampling strategy that will accurately indicate what is actually occurring. This research was focused on development of a method to select a sampling strategy based on a predefined acceptable level of error in pollutant amounts. Adoption of this methodology by those involved in water quality data collection will provide more confidence in the data and its interpretation.
Technical Abstract: Water quality research and monitoring programs often form the basis from which related legislation is derived. Yet, no standard, protocol, or method is available for guiding the selection of a water quality sampling strategy for field runoff and small watersheds. The objective of this study was to develop a methodology that provides guidance in the selection of a water quality sampling strategy for headwater streams (drainage areas < 2500 ha). The developed method is based on the dimensionless unit hydrograph and relationships of measured pollutant concentrations to discharge hydrographs. The methodology was designed for storm events with a specific return interval and a selected acceptable level of error in pollutant load. Nine input parameters (hydraulic length, watershed slope, curve number, drainage area, runoff coefficient, the 10-yr, 1-hr precipitation amount, the 100-yr, 1-hr precipitation amount, the 10-yr, 24-hr precipitation amount, and a recurrence interval) were used to develop the design hydrograph. Both time- and flow-paced sampling techniques were considered. A global sensitivity analysis of the method indicated that time-paced sampling was primarily sensitive to parameters included in the time of concentration calculation (hydraulic length, watershed slope, and curve number). Flow-paced sampling showed some sensitivity to all nine input parameters. An example application illustrates the utility of the method. Use of the method should facilitate the selection of water quality sampling strategies for field and small watershed scale studies and aid in budgetary planning for sample collection and analysis. The measurements taken from the recommended sampling strategy will provide more confidence in the pollutant storm load estimates.