Regional curves, which relate bankfull channel dimensions and discharge to watershed drainage area, are developed to aid in identifying the bankfull stage in ungaged watersheds, and estimating the bankfull discharge and dimensions for river studies and natural channel design applications. This study assessed 26 stable stream reaches in two hydro‐physiographic regions of the Florida Coastal Plain: the Northwest Florida Coastal Plain (NWFCP) and the North Florida Coastal Plain (NFCP). Data from stream reaches in Georgia and Alabama were also used to develop the Florida regional curves, since they are located in the same hydro‐physiographic region. Reaches were selected based on the presence of U.S. Geological Survey gage stations and indicators of limited watershed development (e.g., <10% impervious surface). Analyses were conducted to determine bankfull channel dimensions, bankfull discharge, average channel slope, and Rosgen stream classification. Based on these data, significant relationships were found between bankfull cross‐sectional area, width, mean depth, and discharge as a function of drainage area for both regions. Data from this study suggested that bankfull discharges and channel dimensions were larger from NWFCP streams than from Coastal Plain streams in North Carolina and Maryland. Bankfull discharges were similar between NFCP and Georgia coastal plain streams; therefore, the data were combined into one regional curve. In addition, the data were stratified by Rosgen stream type. This stratification strengthened the relationships of bankfull width and mean depth as a function of drainage area.

The Bank Assessment of Nonpoint source Consequences of Sediment (BANCS) framework allows river scientists to predict annual sediment yield from eroding streambanks within a hydrophysiographic region. BANCS involves field data collection and the calibration of an empirical model incorporating a bank erodibility hazard index (BEHI) and near-bank shear stress (NBS) estimate. Here we evaluate the applicability of BANCS to the northern Gulf of Mexico coastal plain, a region that has not been previously studied in this context. Erosion rates averaged over two years expressed the highest variability of any existing BANCS study. As a result, four standard BANCS models did not yield statistically significant correlations to measured erosion rates. Modifications to two widely used NBS estimates improved their correlations (r 2 = 0.31 and r 2 = 0.33), but further grouping of the data by BEHI weakened these correlations. The high variability in measured erosion rates is partly due to the regional hydrologic and climatic characteristics of the Gulf coastal plains, which include large, infrequent precipitation events. Other sources of variability include variations in bank vegetation and the complex hydro-and morphodynamics of meandering, sand bed channels. We discuss directions for future research in developing a streambank erosion model for this and similar regions.(KEY TERMS: geomorphology; streambank stability; streambank erosion; bank erodibility hazard index; nearbank shear stress; Rosgen; root density; stream restoration; erosion prediction.) McMillan, Mitchell, Johan Liebens, and Christopher Metcalf, 2017. Evaluating the BANCS Streambank Erosion Framework on the Northern Gulf of Mexico Coastal Plain.

Unpaved road‐stream crossings increase sediment yields in streams and alter channel morphology and stability. Before restoration and sedimentation reduction strategies can be implemented, a priority listing of unpaved road‐stream crossings must be created. The objectives of this study were to develop a sedimentation risk index (SRI) for unpaved road‐stream crossings and to prioritize 125 sites in the Choctawhatchee watershed (southeastern Alabama) using this model. Field surveys involved qualitative and quantitative observations of 73 metrics related to waterway conditions, crossing structures, road approaches, and roadside soil erosion. The road‐stream crossing risk analyses involved elimination of candidate metrics based on redundancy, skewness, lack of data, professional judgment, lack of nonzero values, unbalanced box plots, and limited ranges of values. A final selection of 12 metrics formed the SRI and weighed factors involving soil erodibility, road sedimentation abatement features, and stream morphology alteration. The SRI was organized into narrative categories (excellent, good, fair, poor, and very poor) based on the distribution of scores. No excellent sites (scores ≥55) were found in this study, 17 (20.7%) were good (low sedimentation risk), 37 (45.1%) were fair (moderate sedimentation risk), 26 (31.7%) were poor (high sedimentation risk), and two (2.5%) were very poor (high sedimentation risk). There was no significant difference in SRI scores among crossing structure type (round culverts, box culverts, and bridges) (H = 4.31, df = 2, p = 0.058). A future study of the Choctawhatchee watershed involving the same study sites could assess the success of restoration plans and activities based on site score improvement or decline.

Large wood has important structural and functional roles in streams but there is little information on large wood dynamics in the southeastern coastal plains, USA. In this study, we surveyed 35 streams in the Choctawhatchee River watershed of southeastern Alabama. These streams were broadly classified into three categories based on land use: urban, forest, and mixed (agriculture plus forest). The number, volume, and functions of large wood were quantified. Pool number, pool spacing, and drainage areas of each stream were measured along with assessment of macroinvertebrate assemblages. Large wood number and volume plus pool number and spacing were used to examine the relationship among large wood characteristics and functions, pool characteristics, drainage area, and attributes of macroinvertebrate assemblages including species richness, Shannon-Wiener diversity (H 0 ), number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species, and the Invertebrate Community Index (ICI -a multimetric index that reflects biological integrity of streams). There were significant differences in large wood number and volume among the three different stream categories, with highest large wood number and volume in forest streams. More pools and storage sites for sediment and organic matter were found in forest streams than urban and mixed streams. Large wood appeared to be positively related to macroinvertebrate assemblages, as species richness, H 0 , EPT, and ICI were generally higher in forest streams as compared to those of urban and mixed streams. The outcome of this study suggests that large wood contributes to the physical and biological complexity of streams in the southeastern coastal plain streams of the USA.