Differing Levels of Forestry Best Management Practices at Stream Crossing Structures Affect Sediment Delivery and Installation Costs

Abstract

Forestry best management practices (BMPs) are used to reduce sedimentation from forest stream crossings. Three BMP treatments (BMP´, BMP-std, and BMP+) were applied to three forest road stream crossings (bridge, culvert, and ford). BMP´did not meet existing BMP guidelines, BMP-std met standard recommendations, and BMP+ treatments exceeded recommendations. Following BMP applications, three simulated rainfall intensities (low, medium, and high) were applied in order to evaluate sediment delivery from crossing type and BMP level. During rainfall simulation, sediment concentrations (mg/L) were collected with automated samplers and discharge (L/s) was estimated to calculate total sediment loading. Costs of stream crossings and BMP levels were also quantified. Mean sediment associated with the three stream crossings were 3.38, 1.87, and 0.64 Mg for the BMP´, BMP-std, and BMP+ levels, respectively. Ford, culvert, and bridge crossings produced 13.04, 12.95, and 0.17 Mg of sediment during construction, respectively. BMP enhancement was more critical for sediment control at the culvert and ford crossings than at the bridge. Respective costs for BMP´, and BMP+ levels were $5,368,$5,658,and $5,858 for the bridge; $3,568, $4,166 and $4,595 for the culvert; and $180, $420 and $1,903 for the ford. Costs and sediment values suggest that current standard BMP levels effectively reduce stream sediment while minimizing costs.

Best Management Practices Influence Modeled Erosion Rates at Forest Haul Road Stream Crossings in Virginia

“…Culverts are advantageous for logging roads because they are simple to install, can carry heavy payloads without complex calculations of weight limits, and can be either temporary or permanent (Morris et al. ). Disadvantages of culverts include placement of fill dirt in the stream channel with associated sedimentation, improper sizing for water yields, increased downstream water velocity and scouring, restriction of stream aquatic passage, and problems associated with culverts becoming clogged (Warrington et al.…”

“…However, fords tend to allow increased stream sedimentation due to the repeated churning of stream sediments, and their use is limited by appropriate weather conditions (Morris et al. ). We found that fords were used for 12%–28% of the haul road crossings across all regions.…”

“…; Morris et al. ) to categorize BMP implementation on roads and stream crossings (Figure ). Stream crossing approaches that were rated as BMP‐standard showed evidence of preharvest planning based on the selection of crossing location, slope, and soils, and their crossing structures were correctly sized for watershed acreage and flow pattern (Table ).…”

“…; Morris et al. ). As long as sufficient maintenance is performed, erosion tends to decline as roads age; anomalies usually occur due to mass failures of culverted stream crossings (Elliot et al.…”

“…Morris et al. () evaluated instream sediment concentrations and found that the lowest level of BMP bridge treatment (BMP−) was a better BMP option than the higher BMP levels used with the culvert and ford stream crossings tested. Temporary bridges are less commonly used on permanent truck roads, but they are good options for temporary truck roads.…”