Forestry best management practices for erosion control in haul road ditches near stream crossings

Abstract

Poorly designed and maintained forest road stream crossings can directly link erosion sources to streams. Forestry best management practices (BMPs) provide techniques that are useful for preventing sedimentation associated with ditch erosion. However, few studies have quantified ditch BMP sediment reductions. Thus, our primary objective was to evaluate erosion control effectiveness due to ditch BMPs and secondarily to quantify ditch BMP implementation costs. Sixty ditch segments near stream crossings were reconstructed, and five ditch BMP treatments were applied using a completely randomized design resulting in 11 to 13 replications per treatment. Ditch BMP treatments were (1) bare ditch (Bare), (2) grass seed with lime fertilizer (Seed), (3) grass seed with lime fertilizer and erosion control mat (Mat), (4) rock check dams (Dam), and (5) completely rocked (Rock). Silt fence sediment traps and sediment pins were measured over one year to determine treatment effectiveness. Trapped sediment deposits indicated that median erosion rates were greatest for Dam (6.14 Mg ha−1 y−1 [2.74 tn ac−1 yr−1]), followed by Bare (4.92 Mg ha−1 y−1 [2.19 tn ac−1 yr−1]), Rock (1.73 Mg ha−1 y−1 [0.77 tn ac−1 yr−1]), Seed (1.04 Mg ha−1 y−1 [0.46 tn ac−1 y−1]), and Mat (0.82 Mg ha−1 y−1 [0.37 tn ac−1 yr−1]). Results suggested that Mat treatments had significantly lower erosion rates than Bare and Dam, while Rock and Seed provided intermediate levels. Costs of BMP treatments were least expensive for Seed (US$6.10 approach−1), followed by Mat (US$21.33 approach−1), Dam (US$71.43 approach−1), and Rock (US$141.08 approach−1). Results suggest that erosion began to accelerate disproportionately when bare soil levels were between 30% and 50%; therefore, minimum soil cover of 50% is recommended for ditches.