MODELING STREAM DISCHARGE RELATIONSHIPS IN TIDAL CREEKS: IMPLICATIONS FOR STORM WATER MANAGEMENT AND SEA LEVEL RISE

Discharge rating curves are commonly used by hydrologists and engineers to estimate the volumetric flow rate (stream discharge) as a function of water depth in the stream (stream stage). Field measurements are used to calibrate the rating curve functions, which can be influenced by site-specific conditions such as geomorphology, roughness, and sedimentation. Developing discharge rating curves is difficult for tidal streams due to the two-way flow conditions. The bidirectional tidal flow creates conditions where the discharge is different for the same stage depending on whether the tide is falling (ebbing) or rising (flooding). To address this for tidal creeks in the Charleston, SC estuary, we have modeled stream discharge as a function of time during the tidal period, relative to a consistent water level. For example, high water slack (HWS) is the time during the tidal period when discharge is equal to zero at the high tide stream stage. Using this approach, one can estimate the flood and ebb volumes through the standard time vs. discharge relationship. We will present examples of the asymmetry of stream discharge and discuss the importance of these relationships for understanding storm water management and sea level rise impacts.

This research builds on recent research on modeling tidal discharge in several estuarine creeks dominated by salt marsh wetlands. Stream discharge data measured to estimate volumetric discharge and develop a time vs. discharge model with the objective of better predicting discharge rates and volumes of tide water inundation compared to storm-event runoff and baseflow. Geomorphological characteristics of the creeks, including width, depth, and water velocity were also measured. One broader impact of this work is to improve storm water mitigation practices in urbanizing coastal areas.