Incorporating digital data into rapid geomorphic assessments

Abstract

Channel widening and migration can lead to sediment pollution and can be indicative of an imbalanced stream system. Rapid Geomorphic Assessments (RGAs) are on-site methods used to rank stream reaches in terms of stability. RGAs are relatively easy and quick to perform. Subjective measurements and on-site estimates of reach-length parameters create uncertainty in the RGAs. The primary objective of this study was to develop digital RGA methods that integrate readily available data and resources. Digital methods were developed and compared to historical site assessments. Then, the methods were validated by comparing digital RGAs to on-site assessments on several different streams. The digital methods included several different resources, including LIDAR for streambank measurements, Web Soil Survey for bank material and vegetation metrics, and Google Earth to perform visual assessments needed for specific RGAs. Study areas for the validation included second to fourth order streams in Oklahoma in the Ozark Highlands, the Central Great Plains, and the Cross Timbers ecoregions. The resulting digital RGAs performed reasonably well, successfully ranking stream reaches in the same stability ranking as the on-site assessment 38% of the time for two commonly used RGAs: Bank Erosion Hazard Index (BEHI) and the Channel Stability Index (CSI). The digital CSI performed better in the development stage with an 83% success rate. The decrease in performance could be due to several compounding factors such as channel visibility and image availability on Google Earth. Specific metrics should continue to be measured on-site to improve the accuracy of the digital RGAs. For example, a difference of up to twenty points can be avoided if the primary bank material is identified on-site. This project has illustrated the possibility that digital data can be successfully incorporated into RGAs, where digital RGAs have several benefits including the reduced time to assess larger areas and no longer being dependent on land access.