Stream Crossings
BMPs
Avoid
Culvert Installation
Woody Fill
An effort has been made to italicize technical words or phrases and clearly define them in the glossary.
Stream crossings are sometimes necessary for access to forestlands. All crossings need to be planned to minimize environmental impacts. Specific practices are recommended in this section to assure minimum impacts on water flow and aquatic organisms. Bridges, culverts, and fords are all acceptable stream crossings when matched to the site and installed properly.
Bridge construction across navigable waterways is under the jurisdiction of the South Carolina Department of Health and Environmental Control DHEC.* (Opens in new window) Permanent bridges (those that would remain in place for a period greater than six months) must meet higher standards than temporary bridges. Anyone planning to construct a bridge across a navigable waterway must contact DHEC for permit application forms and technical design information.
*DHEC: 2600 Bull St., Columbia, S.C. 29201 (803-734-5360)
BMPs
- Cross streams at right angles except where prevented by geologic features.
- Keep approaches to stream crossings to as gentle a slope as practical.
- Use drainage structures, such as water turnouts or broadbased dips, on both sides of a crossing as needed to prevent road and ditch runoff from entering the stream.
- Ensure proper sizing and installation of culverts(Table 1).
- Stabilize disturbed soil around crossings soon after construction (Table 2).
- Use a licensed forester or other qualified professional to locate stream crossings prior to road construction to minimize impacts.
- Consider using portable bridges instead of culverts.
- Follow all BMPs listed under Forest Wetland Road Construction .
Avoid
- Using soil as fill material except when installing culverts. Allowing runoff from roadside ditches to flow directly into streams at the crossings.
- Altering the flow of the stream.
Culvert Installation
- Place culvert on the grade of the existing stream channel.
- Install culverts which are long enough to extend beyond the toe of the fill slopes.
- Compact backfill material to prevent water from seeping around the culvert.
- Cover the culvert with enough fill to prevent damage by traffic.
- If erosion is a problem, construct a headwall on the inlet side and an apron of rip-rap at the outlet, if the outlet is placed above the toe of the fill.
- Stabilize disturbed soil. If mulch and seed are used, refer to Table 2.
Woody Fill
Woody material may be used as fill to protect stream banks and bottoms in crossing small intermittent and ephemeral streams with well-defined channels if:
- Soil is not introduced into the stream with the woody fill. Soil blocks the pore space among the woody debris, impeding drainage and increasing the amount of sediment in the watercourse.
- Stream flow is not blocked or diverted.
- Woody material that restricts flow of water is removed.
Table 1: Recommended Diameters for Permanent/Temporary Culverted Crossings
| DRAINAGE AREA (acres) | LOWER COASTAL PLAIN | UPPER COASTAL PLAIN | PIEDMONT | MOUNTAIN |
|---|---|---|---|---|
| PERMANENT | ||||
| 10 | 24" | 12" | 30" | 24" |
| 50 | 36" | 18" | 48" | 48" |
| 100 | 48" | 24" | 54" | 60" |
| 200 | 60" | 36" | 72" | 72" |
| TEMPORARY | ||||
| 10 | 12" | 12" | 18" | 12" |
| 50 | 18" | 12" | 30" | 24" |
| 100 | 24" | 18" | 36" | 30" |
| 200 | 30" | 24" | 42" | 36" |
Temporary culverts are sized for storm flows with a two-year -recurrence interval. Permanent culverts are sized for storm flows with 25-year-recurrence intervals. Multiple smaller culverts designed to carry equivalent water flow can be substituted for the above culvert sizes.
For example:
Two 48" culverts can be substituted for a 60" culvert.
Two 54" culverts can be substituted for a 72" culvert.
An alternative is a combination of a smaller culvert and rock surfaced road dips where the culvert is sized for annual storm flows, and the rock surfaced road dip is designed to handle the flow from larger storm events. Landowners are encouraged to contact a local U.S. Natural Resources Conservation Service representative or other qualified professional to design culverted crossings specifically for each site.
Table 2: Recommendations for Seeding, Mulching, and Fertilizing
Roads, Fills, and Other Disturbed Areas
| AREA | SPRING AND EARLY SUMMER | LATE SUMMER,FALL, AND EARLY WINTER | ||
|---|---|---|---|---|
| MOUNTAINS | Kentucky 31 Fescue (early spring) | 30 lbs./acre | Kentucky 31 Fescue | 30 lbs./acre |
| (or) Orchard Grass (late spring) | 12 lbs./acre | Annual Rye | 10 lbs./acre | |
| Browntop Millet | 10 lbs./acre | * Unscarified Sericea Lespedeza | 25 lbs./acre | |
| *Scarified Sericea Lespedeza | 20 lbs./acre | |||
| PIEDMONT | Kentucky 31 Fescue (early spring) | 30 lbs./acre | Kentucky 31 Fescue | 30 lbs./acre |
| Browntop Millet | 10 lbs./acre | Annual Ryegrass | 5 lbs./acre | |
| Bahia | 10 lbs./acre | Annual Rye | 10 lbs./acre | |
| *Scarified Sericea Lespedeza | 20 lbs./acre | * Unscarified Sericea Lespedeza | 25 lbs./acre | |
| COASTAL PLAIN | Bermuda grass (hulled) | 4 lbs./acre | Bahia | 30 lbs./acre |
| Bahia | 25 lbs./acre | * Unscarified Sericea Lespedeza | 60 lbs./acre | |
| *Scarified Sericea Lespedeza | 25 lbs./acre | Annual Rye | 20 lbs./acre | |
| Browntop Millet | 10 lbs./acre | |||
| * Sericea may be left off on low erosion hazard areas. NOTE: Fertilize with 800 to 1,000 per acre of 6-12-12. Mulch slopes with 4,000 lbs. small grain straw or 5,000 lbs. hay per acre. | ||||
Contents
Streamside Management Zones /
Forest Road Construction /
Timber Harvesting /
Site Preparation /
Reforestation /
Prescribed Burning /
Pesticides /
Fertilization /
Minor Drainage /
Endangered Species Act /
Additional Management Options: Wildlife Management /
Glossary
Forest Management/ Reference Resources / Environmental Forestry/ Braided Stream Systems