Rapid geomorphic assessment walkabouts as a tool for stream mitigation monitoring

Abstract

Monitoring of compensatory stream mitigation projects conventionally relies on spatially discrete geometric data and habitat assessments collected from representative reaches. Project success is evaluated by extrapolating site-scale metrics such as rapid bioassessment protocol (RBP) scores and time-series changes in width-to-depth ratios to adjacent reaches. For example, an excellent RBP score at one location is used to infer excellent habitat in nearby reaches. This paper compares spatially discrete and continuous monitoring data from 38 km of restored stream length on a stream mitigation project in central Kentucky to document how conventional site-level metrics may not represent conditions in adjacent reaches, particularly on projects plagued by post-construction geomorphic instability (e.g., headcut migration, propagation of bank erosion, and chute cutoff formation). Over a 5-year monitoring period, rapid visual assessment walkabouts documented project-scale geomorphic process trajectories that were not captured by conventional site-specific monitoring. Early detection of geomorphic instability from this rapid monitoring approach facilitated cost-effective and tailored adaptive management (e.g., planting of live stakes to arrest bank erosion). Full-census walkabouts can thereby help to improve mitigation credit valuation, enhance long-term habitat protection, and facilitate successful steam restoration outcomes.