Evaluation of structural best management practices 20 years after installation: Black creek watershed, Indiana

ABSTRACT:

Millions of dollars have been spent on agricultural watershed projects across the nation, but little is known about the long-term impacts of watershed management and protection efforts. Information pertaining to long-term condition and water quality impact of best management practices (BMPs) is scarce. Evaluation methods that estimate the current condition of the practice based on visual inspection and comparison to selected original design dimensions were developed for grassed waterways, grade stabilization structures, field borders and parallel terraces. The evaluation tools were tested for validity using an expert panel approach and for reliability based on inter-rater correlation. The evaluation tool's three-point scale rating system assigns a score of three to a BMP that was fully functional and still met its original design purpose and a score of one to a BMP that no longer performed as designed. The newly developed evaluation tools were applied to a subset of structural BMPs implemented in the late 1970s in a major watershed management project in an Indiana watershed. One-third of the BMPs no longer remain. Those BMPs that remain today are in fair condition and are reasonably functional. Grassed waterways and terraces were most likely to remain, while the field borders that still existed had the highest condition score. This study suggests that BMPs can in some cases continue to function past their design life, but serves as a reminder that BMP functional life is limited, a fact that needs to be explicitly considered in conservation and watershed planning.