Stream crossings must be designed, constructed and maintained to safely handle expected vehicle loads and to minimize disturbance of streambanks, channels and, ultimately, aquatic organisms.  Consider streambed material, stream size, storm frequency, flow rates, intensity of use (permanent or temporary) and the passage of fish when planning crossings.  The USDA Natural Resources Conservation Service (NRCS), or a private consultant can help with designing fords and culverts.  To design a bridge, contact a private consultant or experienced contractor

BMPs for Stream Crossings Use soil stabilization practices on exposed soil at stream crossings.  Use seed and mulch and install temporary sediment control structures such as straw bales or silt fences immediately following construction to minimize erosion into streams.  Maintain these practices until the soil is permanently stabilized.  Please refer to the section about soil stabilization, below.

• Design, construct and maintain stream crossings to avoid disrupting the migration or movement of fish and other aquatic life.Bridges or arch culverts that retain the natural stream bottom and slope are preferred for this reason.
  
  
• Install stream crossings using materials that are clean, non-erodible and non-toxic to aquatic life.
  
  
• Install stream crossing structures at right angles to the stream channel.
  
  
• Minimize channel changes and the amount of excavation or fill needed at the crossing.
  
  
• Limit construction activity in the water to periods of low or normal flow.  Keep use of the equipment in the stream to a minimum.
  
  
• Construct a bridge or place the fill over a culvert higher than the road approach to prevent surface road runoff from draining onto the crossing structure and into the stream (Figure C-1).
  

Figure C-1.  Place fill directly over a culvert higher than the road approach to prevent surface road runoff from draining onto the crossing structure and into the stream. (Adapted from Wisconsin Department of Natural Resources, 1995.)

• Stabilize approaches to bridge, culvert and ford crossing with aggregate or other suitable material to reduce sediment entering the stream.
  
  
• Anchor temporary structures on one end with a cable or other device so they do not float away during high water.Install them so they can be easily removedwhen no longer used, regardless of the season.
  
  
• Avoid areas with riffles and pool complexes, wetlands, mudflates or vegetatedshallows which are considered special aquatic sites under the Clean Waters Act (CWA), Section 404 and have strict requirements for permits.

Divert road drainage into undisturbed vegetation, preferably outside the SMA so that the drainage does not directly enter the stream (Figure C-2) Also refer to Diversion Structures on page 50.

Pipe Culverts for Stream Crossings · Install pipe culverts long enough so that road fill does not extend beyond the ends of a culvert.

Install permanent culverts that are large enough to pass flood flows and are a minimum of 12 inches in diameter.  Culverts that are too small can plug up with debris and result in the road washing out or in flooding upstream.

Iowa law states that the landowner and/or contractor are responsible to obtain a flood easement from any affected property owners upstream of culvert crossing that are not designed to pass the 100-year flood.

The USDA Natural Resources Conservation Service, or a private engineering consultant can help with sizing culverts.

Figure not available

Figure C-3. Install culverts so there is no change in the stream bottom elevation. (Adapted from Wisconsin Department of Natural Resources, 1995.)

Install culverts so there is no change in the stream bottom elevation (Figure C-3). Culverts should not cause damming or pooling.

Firmly pack fill material around culverts, particularly around the bottom half.  Cover the top of culverts with fill to a depth of one-third of the pipe diameter or at least 12 inches, whichever is greater, to prevent crushing (Figure C-4).
 

Figure not available

Figure C- 4.  Installation of culverts.  (Adapted from Montana Department of State Lands, 1992.

Use riprap around the inlet of culverts to prevent water from eroding and undercutting the culvert (Figure C-5a and 5b).  For permanent installations, use filter fabric under the riprap.  In addition, consider using flared culvert end sections for inlets.

Keep culverts clear and free of debris so that water can pass unimpeded at all times.  This is especially important in areas where beaver are present.
 

Figure C-5b. Use geotextile filter fabric for permanent installations.  (Adapted from Wisconsin Department of Natural Resources, 1995.)

Fords

Use fords for crossing dry streambeds or where fording would cause minimal water quality impacts.

Locate fords where streambanks are low.

Streambed should have a firm rock or gravel base.  Otherwise, install stabilizing material such as reinforced concrete planks, crushed rock, riprap or rubber mats on streambeds.

Road Construction and Drainage - BMPs

The most effective method to control erosion on woodland roads is to keep water from accumulating on the road surface.  Fast-moving water can easily erode soil from road surfaces and ditches, but road erosion can be controlled when water drains off the road surface and is dispersed into vegetation and ground litter.

Design and construct roads to remove water from road surface to keep the road dry and structurally sound.  Figure C-6 shows three common road designs: crowned, outsloped and insloped.  Install insloped roads with ditches and adequate cross drainage.  Outsloped roads (usually outsloped 2-4%) are less expensive to construct and maintain; use them on roads with moderate gradients and stable soils.
 
 

Figure C-6.  Typical road designs form drainage and stability. (Adapted from Wisconsin Department of Natural Resources, 1995.)

Construct stable cut-and-fill slopes that will revegetate easily, either naturally or artificially.

Do not bury debris in the road base.  It causes uneven settling that can led to  erosion and frost-heaving that creates mud holes.

Compact the road base material or allow it to settle before using the road.  This will reduce the amount of water that soaks into it, increasing the road’s carrying capacity, reducing road maintenance and reducing erosion.

Face the road with gravel where steep grades, erodible soils or high traffic volume make the potential for surface erosion significant.

Locate gravel pits outside SMAs, using proper location, development and soil stabilization
practices to minimize erosion from the pits.

Drainage Structures - BMPs

Road-drainage structures include cross drains (pipe culverts, open-top culverts, broad-base dips and water bars) and water-diversion structures.  Cross drains allow water from roadside ditches to move from one side of the road to the other.

Where necessary to protect water quality, install road drainage structures to remove storm water or seepage from the road surface and ditches.  Space these structure at intervals close enough to minimize waterflow volume and speed, avoiding ditch erosion.  As road grades increase, use drainage structures more often.  See Table C- 1 below.

Provide erosion protection for outflows from road drainage structure to minimize erosion and disperse the water, allowing it to soak into the soil.  Riprap, mulch and/or seeding may be necessary.  Please refer to the section on soil stabilization.

Table C- 1.  Recommended distances between drainage structures on woodland roads and skid trails.
Road grade% Distance betweenwaterbars (feet) Distance between broad-based dips and cross-drain culverts (feet).
 

Figure C-7.  Cross-drain culvert. (Adapted from Wisconsin Department of Natural Resources, 1995.)

  Pipe Culverts for Cross Drains

Install pipe culverts to provide cross drainage on roads grades at regular intervals immediately above steep grades, below bank seepage and where water will run onto log landings or woodland roads.

Install pipe culverts long enough so that road fill does not extend beyond the end of a culvert.

Install cross drain pipe culverts at grades at least 2% more than the ditch grade and angled 30 to 45 degrees to improve inlet efficiency (Figure C-7).

Select the size of cross-drain culverts according to the size of the road and area drained by the ditch.  To avoid clogging, permanent culverts should be at least 12 inches in diameter.  The USDA Natural Resources Conservation Services or a private engineering consultant can help with sizing culverts.

Install pipe culverts on a surface of compacted granular material.  Firmly pack fill material around culverts, particularly around the bottom half.  Cover the top of the culvert with fill to a depth of one-third of the pipe diameter, or at least 12 inches (whichever is greater) to prevent crushing (Figure C-4).

Use riprap around the inlet of culverts to prevent water from eroding and undercutting the culvert.

Open-Top Culverts

Open-top culverts provide cross drainage and road surface drainage (Figure C-8) and are usually installed on seasonal or temporary roads.

Install open-top culverts to provide cross drainage immediately above steep grades, below bank seepage, where water will run onto log landings or woodland roads and on road grades at regular intervals.

Clean open-top culverts frequently since they easily fill in with debris.

Broad-Based Dips

Broad-based dips can provide cross drainage and road-surface drainage for roads and skid trails with a gradient of 15% or less (Figure C-9).  Broad-based dips can be used instead of culverts, usually at lower cost and with lower maintenance.  Dips are not used for draining seeps, or for intermittent or permanent streams.

Construct broad-based dips deep enough to provide adequate drainage and wide enough to
allow trucks and equipment to pass safely.

Place a surface of crushed stone or gravel on the dip and mound for soils and conditions where rutting may occur.

Water Bars

A water bar is a shallow trench with a mound (or berm) which provides cross drainage and intercepts runoff from skid trails, recreational trails, firebreaks, or inactive or closed roads.  (Figure C-10).  Constructing a water bar will minimize erosion and provide conditions for natural or artificial revegetation.

Place water bars at a 30 to 45 degree angle with a cross drainage grade of 2%.
 

Figure C-10.  Water bar. (Adapted from Wisconsin Department of Natural Resources, 1995.)

Diversion Structures

Diversion ditches, or berms, divert water away from roads and side ditches and channel it into vegetation (Figure C-2).  These structures are often used before stream crossings to ensure that water will be diverted into vegetation and not directly into a stream, lake or wetland.

Construct diversion ditches so they intersect the roadside ditch at the same depth and are turned down slope 1% to 3% (Figure C-2)

Soil Stabilization - BMPs

Soil stabilization practices are used where soil is exposed and natural revegetation is inadequate (i.e., road development, skid trails and landings) to prevent soil erosion and subsequent sedimentation into streams, lakes and wetlands.  This occurs during roads construction and when the road system is active or inactive.  Practices include mulching, seeding and installing sediment control structures.

It is always more efficient and cost effective to prevent erosion than it is to repair damage after the fact.

Mulching and Seeding

Use mulch and/or seed where necessary to minimize soil erosion.

Mulch, such as straw, woodchips or bark, retains soil moisture - important for seed germination and protects the soil surface from erosion due to runoff and raindrop impact.

Mulch can be used to: (1) promote natural revegetation or (2) protect seeds that have been spread over an area.  If you seed, apply mulch immediately afterward.  Netting may be necessary to hold mulch in place on steep slopes or on areas where water flow concentrates.

Seed mixtures should include fast growing species for quick soil protection plus perennial species for longer soil protection until native vegetation returns to the site.  Recommendations for seed mixes that are best for specific regions in Iowa are available from your District IDNR Forester, Wildlife Biologist or USDA Natural Resources Conservation Service office.

A suggested minimum generic seed mixture, applied at the rate of 55 lbs./acre, is as follows:

White Dutch clover  10 lbs./acre
Perennial rye grass  10 lbs./acre
Annual rye grass  20 lbs./acre
Creeping red fescue  15 lbs./acre

Table C-2 is provided to assist you in determining the area (acres) of a specified length and width of road surface.

Table C-2.  Road Surface Area Determination (acres)

Sediment Control Structures

Install sediment control structures where necessary to slow the flow of runoff and to trap sediment until vegetation is established at the sediment source.  Sediment control structures include straw bale fencing, silt fencing and sediment traps (Figures C-11).

Maintain, clean, or replace sediment-control structure until areas of exposed soil are stabilized.
 

Road Maintenance

Roads must be well maintained or water quality protection structures may quickly degrade.  For both active and inactive roads, follow BMPs in the Soil Stabilization section on pages 34-36.

Active Roads

Inspect the road system at regular intervals, especially after heavy rainfall, to detect problems and to schedule repairs.

Clear debris from culverts, ditches, dips and other drainage structures to decrease clogging that can lead to washouts.  Place the debris where it cannot be washed back into these structures or into open water.

Keep traffic to a minimum during wet periods and spring breakup to reduce maintenance needs.

Shape road surfaces periodically to maintain proper surface drainage.  Fill in ruts and holes with gravel or compacted fill as soon as possible to reduce erosion potential.

Remove berms along the edge of the road if they will trap water on the road.

When dust control agents are used, apply them in a manner that will keep these compounds from entering lakes, streams and groundwater.  Consult a qualified road engineer from the County Highway Commissioner’s office or Iowa Department of ransportation for assistance in selecting the appropriate chemicals and amounts.

Note: It is illegal to spread oil on road,land or water in Iowa.

Inactive Roads

When woodland roads are inactive for extended periods, closing the system will help to protect the road surface and the water quality protection structures.  Consider erecting a barrier to traffic such a gate or berm and post “Closed” signs at the entrance of temporarily closed roads.  Stating the length of time and/or reason for closure and inviting acceptable uses may be helpful to assure compliance.

Remove all temporary drainage and stream crossing structures.

Shape all road system surfaces to maintain proper surface drainage, if necessary.

Install water bars where necessary.  Please refer to the section on water bars and follow recommendations in Table C- 1.

Inspect and maintain road surfaces, permanent drainage and streamcrossing structures (ditches, culverts, bridges, etc.) to minimize erosion.

Federal Requirements for Woodland Roads in Wetlands

The following 15 BMPs must be implemented in order to qualify for the silvicultural exemption from a federal section 404 permit when building a temporary or permanent road or skid trail in a wetland (33 CFR part 323.4).  The silvicultural exemption is only applicable when the primary purpose of the roads is for normal silvicultural purposes.  This listing is an attempt to explain the 15 BMPs in lay language.  The exact language of the law may be obtained by contacting the Army Corps of Engineers.

1. Limit the number, length and width of roads and skid trails to the minimum necessary to accomplish the landowner’s objective.

2. Locate roads outside streamside management areas except at stream crossings.  Formore information, please refer to the section on Streamside Management Areas.

3. Road fill must be bridged, culverted, or otherwise designed to prevent restriction ofexpected flood flows.

4. Properly stabilize and maintain road fill during and after road construction to prevent erosion.

5. While building a road with fill material, minimize the use of road construction equipment in the wetland area.

6. Minimize disturbance of vegetation while designing, constructing and maintaining roads.

7. Correctly design, construct and maintain wetland road crossings to avoid disrupting the migration or movement of fish and other aquatic life.

8. Use fill from upland sources whenever feasible.

9. Place fill in a way that does not take or jeopardize the continued existence of athreatened or endangered species (as defined under the Endangered Species Act or adversely modify or destroy the critical habitat of such species.

10. Avoid placing fill in breeding and nesting areas for migratory waterfowl, in spawning areas and in wetlands if practical alternatives exist.

11. Fill shall not be placed near a public water supply intake.

12. Fill shall not be placed in areas of concentrated shellfish production.

13. Fill shall not be placed in waterbodies or on land regarded as part of the National Wildand Scenic River System.

14. Use fill free from toxic pollutants.

15. Completely remove all temporary fills and restore the area to its original elevation.

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