Watershed

Development, grading, vegetation removal, road construction, drainage modifications, and other land-use changes can alter how precipitation is stored, infiltrated, or conveyed through a watershed. An expert can compare historical and current conditions, runoff patterns, aerial imagery, drainage features, and available models to determine whether a particular change is consistent with the observed watershed response. Because watershed conditions are interconnected, activities upstream can affect downstream streamflow and water quality.

The analysis may compare subwatershed boundaries, slopes, soils, land cover, drainage paths, precipitation, erosion evidence, stream conditions, and changes over time. Rather than assuming that the nearest property is the source, the expert can determine whether the proposed source is hydrologically connected to the affected location and whether the timing and pathway are consistent with the physical evidence.

Useful materials may include topographic and drainage maps, site plans, historical and current aerial imagery, land-use records, grading plans, precipitation and streamflow data, erosion-control records, photographs, watershed studies, model files, water-quality or sediment data, and records of upstream development or drainage changes. Preserving dated materials is particularly useful when the dispute concerns how watershed conditions changed over time.