Operational forest stream crossings effects on water quality in the Virginia Piedmont

Abstract

10–40%. Many ephemeral and intermittent streams in this landscape have unstable banks because they are recovering erosion gullies caused by abusive agricultural practices used in the region in the 1700s and 1800s (Trimble 1974). Common soils of the approaches and stream crossings include the Wehadkee, Chewacla, Wilkes, Appling, Madison, Codorus, Bremo, and Toccoa soil series (USDA Soil Conservation Service 1974). Personnel from three timber procurement organizations and the Virginia Department of Forestry identified potentially suitable stream crossings prior to installation. The first available stream crossings that met the desired criteria was selected, where permission from landowners to make repeated visits could be obtained and where the timing of operations allowed evaluation of the crossing from preinstallation through closure. All stands accessed by the crossings were clearcut harvested and included natural upland hardwood stands and loblolly pine (Pinus taeda L.) plantations. Stream crossings selected were on low-volume forest roads (class 2 permanent roads and class 3 temporary roads) or bladed skid trails (class 4) (Walbridge 1990). The different road classes were included for two reasons, to acquire the desired replications of the crossings in a timely manner and because the different classes represent the overall tract level access system. The roads, skid trails, and crossings included in this study were designed or selected by a company forester or forest engineer and implemented by logging contractors. One difficulty in acquiring the required numbers of stream crossings for the study was caused by the rapid selection and placement of crossings by loggers, which sometimes precluded the required preinstallation measurements. Treatment Description Four stream crossing treatments were evaluated: portable steel skidder bridges (BRIDGE), pole-filled culverts (POLE), reinforced fords (FORD), and standard earth-fill culverts (CULVERT). The initial experimental design sought to install six replications of each crossing structure. However, because of the difficulty in finding more than four sites that were suitable for the FORD, the final design consisted of 6, 6, 4, and 7 replications for the BRIDGE, CULVERT, FORD, and POLE treatments, respectively. Therefore, a total of 23 stream crossings were monitored during the project. The BRIDGE treatment consisted of 9.1–12.2-m (30–40-ft) long steel panels that were 1.2 m (4 ft) wide. Three panels were used for each crossing (Figure 2). POLE crossings used either steel gas line pipes or corrugated steel culverts with pole-sized stems used to fill the stream cross-section (Figure 3). All POLE crossings had stems placed parallel to the pipe as fill; however, some POLE crossings had additional poles or logging mats placed perpendicular to the stream channel to provide a traffic surface. FORD crossings were reinforced with geotextile or mats topped with gravel (Figure 4). Two of four FORD crossings involved simple reinforcements of existing fords on farm roads rather than construction of new fords. CULVERT crossings consisted of either single or double corrugated steel pipes with earth fill (Figure 5). In general, BRIDGE and POLE structures were used for temporary crossings on smaller streams, and CULVERT and FORD structures were used for more permanent roads and larger streams. However, all crossing types were used in at least one instance for both permanent and temporary crossings. These uses match the basic attributes of the crossings: BRIDGE and POLE crossings are better suited for temporary crossings on smaller streams and are often used for skid trails. CULVERT and FORD crossings Figure 1. Virginia physiographic provinces and counties showing the location of the 23 stream crossings evaluated in the Piedmont. Figure 2. BRIDGE treatment using portable steel panels for a temporary haul road stream crossing. 124 SOUTH. J. APPL. FOR. 35(3) 2011 D ow naded rom http/academ ic.p.com /sjaf/article-ct/35/3/123/4774842 by gest on 30 Jauary 2020