Forestry Culverts Public View

The culverts in this dataset are required to meet the BMP's under the Alaska Forest Resources and Practices Act. Each culvert was reviewed on-site. Nearly all culverts and the streams they span were surveyed for bed width, pool depth, length diameter, gradient and blockage. Each pipe was given a 1 to 4 (best) rating based on its ability to pass fish. In addition, fish traps were set at all crossings where stream classification was unknown. Surveys were carried out by DNR-DOF and ADFG-Habitat. Terms and descriptions can be found in the following Division of Forestry publication: Implementing Best Management Practices for Timber Harvest Operations. ROAD DRAINAGE 11 AAC 95.295(b) - 1. NUMBER OF DRAINAGE STRUCTURES APPLICABILITY • Construction of drainage systems on forest roads. OBJECTIVES • To avoid exceeding the capacity of the ditch. Runoff flowing down the ditchline must be relieved before it can overwhelm the capacity of the ditch, flooding the road. • To prevent erosion of adjacent cut slopes or roadbed material. As flows increase, so does their capability to cause erosion, especially on steeper grades. • To keep roads constructed on unstable soils well drained. • To control discharge of sediment-laden runoff from a road. Runoff collected by the road drainage system needs to be spread out across the hillside to • avoid erosion that would be caused by a more concentrated flow, and • allow vegetation to filter out suspended sediment. REQUIREMENTS • Install and space drainage structures as necessary to accommodate peak flows or to assure adequate drainage of unstable soils. Inadequate drainage of a road saturates the soil and decreases stability. • Prevent degradation of surface water quality. Sediment-laden runoff from a road needs to be spread out across the hillside so sediment can be filtered out by vegetation. Implementing BMPs for Timber Harvest Operations 51 NOTES • Less frequent spacing of drainage structures is permissible if the parent material of roadbed is not erodible, such as rock or gravel, or the topography is not conducive to erosion. More frequent spacing is required where soil is unstable or where peak flows require more drainage structures to prevent degradation of surface water quality. • To determine whether accumulated flows are eroding cut banks or roadbed material adjoining the ditchline, look for undercutting and slumping of cut banks and widening of the ditchline where sections of the roadbed have been washed away. • To determine whether the ditch capacity is being exceeded, look for places where the ditchline flows have escaped the ditch and flowed down or across the road (scouring of roadbed material). • Ditchline flows need to be reduced where the grade increases, and where soils are highly erodible. • Wetter hillsides require more drainage structures to handle anticipated flows. • If subsurface flow dominates on a well-drained hillside, roads will usually not intercept subsurface flows, requiring fewer drainage structures. • Discharges near surface waters should be minimized, potentially requiring additional relief structures to reduce the drainage area. • Fewer drainage structures may be needed where the terrain prevents runoff from reaching surface waters. • Sediment entering surface waters indicates a need for more drainage structures. • Consider current weather conditions during inspection. Drainage needs will be more obvious on wet days. On dry days, anticipate the needs during extreme weather conditions based on terrain and road material. ───────┬───────────────────────────────────────────────────────────────────────────────────────┬──────────────────────────────────────────────────── ﻿Rating │Does the road segment have enough drainage structures to adequately handle peak flows? │Amount of erosion of roadbed, cutslopes, and fills: ───────┼───────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────── 1 │No │Significant ───────┼───────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────── 2 │No │Throughout the road segment ───────┼───────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────── 3 │Portions of the road do not │On some portions of the segment ───────┼───────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────── 4 │Yes, on most of the road segment │In a few places ───────┼───────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────── 5 │Yes │None ───────┼───────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────────── N/A │No drainage structures were required along the road segment evaluated. │ ───────┴───────────────────────────────────────────────────────────────────────────────────────┴──────────────────────────────────────────────────── 11 AAC 95.295(b) – 2. DRAINAGE STRUCTURES ON NATURAL DRAINAGES APPLICABILITY • Construction of drainage systems on forest roads. OBJECTIVES • To prevent road construction from blocking any natural drainage. • To prevent a road from washing out. Implementing BMPs for Timber Harvest Operations 52 REQUIREMENTS • Install drainage structures on all natural drainages. NOTES • Drainage structures must be capable of handling peak flows (estimate by width and depth of channel at high water mark). • Consider flow restrictions through culverts when determining if they are adequate to handle anticipated flows. • A structure in poor condition will not function to its full capacity and will need to be replaced. ───────┬───────────────────────────────────────────────────────────────────────┬──────────────────────────────────────────── ﻿Rating │Number of natural drainages lacking adequate drainage structures: │Drainages flowed across the road? ───────┼───────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────── 1 │Majority │Yes ───────┼───────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────── 2 │Many │Drainages with inadequate relief ───────┼───────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────── 3 │A few │In places ───────┼───────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────── 4 │Occasional │Some drainage structures have been exceeded ───────┼───────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────── 5 │None │No ───────┼───────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────── N/A │There are no natural drainages along the road segment being evaluated. │ ───────┴───────────────────────────────────────────────────────────────────────┴──────────────────────────────────────────── 11 AAC 95.295(d). OUTSLOPING AND DITCHING ROADS APPLICABILITY • Forest roads utilizing through-cuts or partial/full bench road construction. OBJECTIVES • Provide drainage structures to collect and carry runoff away from a road. Design road so drainage structures intercept and carry runoff from the hillside and inside portions of a crowned road surface. • To help drain the roadbed. Design road so runoff will flow off the surface. REQUIREMENTS • Roads must be outsloped, or ditched on the uphill side. NOTES • When a road is confined by a hillside, runoff from the road and ephemeral drainages from the hillside must be collected. Short sections of road that cut through a ridge may not require a ditch if the road can be graded or banked so runoff will drain off the road within a short distance. • If a ditch is needed on the uphill side of a road, it should be constructed as an integral part of the road, collecting runoff from the hillside and road surface. It should be close enough to the road so a grader can pull and clean it. • Straight sections of road should visually slope to the outside edge of the road. Winding sections should be distinctly banked to direct runoff towards the inside corner of the curve and off the road. • Erosional patterns should show that runoff is rapidly seeking the outer edge and does not flow for an extended distance down the road. ───────┬──────────────────────────────────────────────────────────────┬────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── ﻿Rating │Road segment ditched or outsloped? │Ditch adequate to handle normal flows along road │ │segment? ───────┼──────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 1 │No │N/A ───────┼──────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 2 │Only partially │No ───────┼──────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 3 │Partially │Yes, normal flows ───────┼──────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 4 │Along most of road segment │Yes, peak flows on most of road segment ───────┼──────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 5 │Yes │Yes, peak flows ───────┼──────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── N/A │No ditching or outsloping along the road segment is required. │ ───────┴──────────────────────────────────────────────────────────────┴────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── ───────┬────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── ﻿Rating │On portions of the road segment where no ditch is installed, effectiveness of outsloping the road in directing runoff to and off the edgeof the road: ───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 1 │N/A ───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 2 │Only marginally effective ───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 3 │Somewhat effective ───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 4 │Not entirely effective ───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 5 │Effective ───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── N/A │ ───────┴────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 11 AAC 95.295(f). DIVERT DITCHLINE RUNOFF AWAY FROM SURFACE WATERS APPLICABILITY • Applies to ditches along all forest roads. • Applies to unstable soils and surface waters. OBJECTIVES • To provide ditchline relief prior to the road crossing a surface water. • To avoid directing the discharge from a ditch onto unstable soils. REQUIREMENTS • To the extent feasible, direct ditchline runoff away from unstable soils and surface waters, and onto vegetative areas. NOTES • Discharges should be directed away from stream channels, intermittent stream channels, and unstable soils. • A drainage structure should be provided as close as practical to the stream crossing to relieve the ditchline before flows reach the crossing site. • Drainage relief should be provided where outflows can percolate into the soil, or drainage should be directed through sufficient vegetation to remove suspended sediment before reaching surface waters. • Low spots in the terrain or intervening ridges can be used to intercept discharges from the drainage relief structure, allowing suspended sediment to filter or settle out before reaching adjacent surface waters. ﻿ ───────┬──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── ﻿Rating │When feasible, were drainage features designed or installed to divert ditchline flows away from surface waters or unstable soils along the roadsegment? ───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 1 │No ───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 2 │Yes, along a portion of the segment, but were not very effective. ───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 3 │Yes, along most of the segment, and were somewhat effective. ───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 4 │Yes, generally effective ───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 5 │Yes, ───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── N/A │The road segment crossed no surface waters or unstable soils. ───────┴──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 11 AAC 95.295(i). DO NOT DISCHARGE ONTO ERODIBLE OR FILL SLOPES APPLICABILITY • Applies to discharges from cross drains, culverts or diversion ditches. OBJECTIVES • To prevent erosion and sediment generation. REQUIREMENTS • Outfalls may not discharge onto erodible soils or fill slopes without adequate outfall protection. NOTES • If outfalls are discharging onto erodible soils or fill slopes, ensure adequate protection is provided to prevent erosion of the soil or failure of the fill slope. ───────┬─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬──────────────────────────────────────────────── ﻿Rating │Were protective measures taken to prevent erosion of erodible soils and fill slopes along a portion of the road segment? │Adequacy of measures toprotect against erosion: ───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────── 1 │No. │N/A ───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────── 2 │Along a portion of the road segment. │Occasionally adequate ───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────── 3 │Along much of the road segment │Somewhat adequate ───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────── 4 │Along the whole road segment │Usually adequate ───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────── 5 │Always adequate │ ───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼──────────────────────────────────────────────── N/A │No drainage structures discharged onto erodible soils or fill slopes along the road segment evaluated. │ ───────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴────────────────────────────────────────────────