INFLUENCE OF HIGH-RESOLUTION TOPOGRAPHIC DATA ON PREDICTED WATER SURFACE ELEVATION AND LATERAL CONNECTIVITY IN THE SUNCOOK RIVER

Rivers can transport excess nutrients to coastal areas, resulting in eutrophication. Main channel connectivity with near-stream storage areas can impact the uptake of nutrients, including nitrogen, within a river reach. It is important to understand lateral connectivity under low to medium flows (e.g. 1- to 2-year flood events), which are the effective flows for biogeochemical activity and which have recently become more frequent in the Northeast. This study uses a 1-D hydraulic model (HEC-RAS) to determine the inundation and residence time of channel margins, which are expected to be biogeochemical hotspots for nutrient processing. The study reach is the Suncook River near Epsom, NH, which experienced an avulsion in May 2006, resulting in ongoing channel adjustment. Topography was provided by historical field-surveyed stream cross sections and recently acquired high-resolution Experimental Advanced Airborne Research LiDAR (EAARL-B) data, which utilizes water-penetrating green wavelengths to collect bathymetric data. Understanding the influence of lateral connectivity on fluvial nitrogen uptake will improve estimates of reach-scale uptake, an important ecosystem service and the focus of many stream restoration projects.