Rip-rap or “armor” around both ends of the culvert to protect splash areas or where stream bank is exposed to flow, as in the examples below: 

Road side ditches may be stabilized with rip-rap, sod or mulch-and-seed techniques.

Preventing Soil Erosion on Crossing Sites:

Plant roots stabilize the soil, and stems and leaves slow the water to give it time to percolate slowly into the soil profile.  The potential for severe soil erosion exists after any culvert installation or enhancement project because it displaces or destroys plant material and the layer of litter on the surface.  There are several steps you should take to reduce the amount of soil erosion at your work site.

Unstable soil surrounding this culvert
has begun to erode away.

The 1st step is to protect the work area long before the heavy construction begins:

The use of sand bags, silt fences, straw bales and straw wattles have proven benefits for small construction projects.  Then as the project is progressing, it’s important to leave in place, the greatest amount of existing vegetation as possible.   Assuming the plants/trees do not threaten personal safety. 

After the project is concluded, the 2nd step is to reseed and protect any disturbed soils.  Some good reseeding tips to protect your work site would include:

• If needed roughen the soil surface to provide a better seedbed by breaking through the hydrophobic layer.  A steel rake works well for this, or, depending on the slope, a small tractor drawn harrow could be used.
   

• Add organic material (top soil or black muck) to ensure nutrients are available for seed germination. Add organic
   

• Broadcast the seed.  Seeding rate depends upon the variety of seed used.  Rake or harrow in ¼" to ¾" deep.
   

• If the area is small enough, roll or tamp the seed down to ensure good soil/seed contact.
   

• Spread certified weed-free hay straw as a mulch.  If the area is small, crimp the hay into the soil with a shovel.  This will help keep both soil and seed in place during a significant wind and rain event.
   

• Control weeds as needed by cutting off the flower before it can reseed
   

• Do not use herbicides for broadleaf weed control until after the grass has germinated and developed leaves.

The 3rd step is to stabilize the upland area draining toward the stream crossing.  This task can be safely accomplished by numerous means.  The most commonly used methods are described below:   

Polypropylene Sand Bags are made of woven polypropylene and work well as a temporary solution to detour the path of unwanted runoff during the construction period.  Biodegradable products should be used for all long term work.

There are a variety of products available for erosion control. 
Use biodegradable materials that will not interfere
with long term vegetation development.

Silt fences are made of woven wire and a fabric filter cloth.  The cloth traps sediment from runoff.  These should be used in areas where runoff is more dispersed over a broad flat area.  Silt fences are not suitable for concentrated flows occurring in small rills or gullies. 

To install a (pre-assembled) silt fence, simply unroll, stretch and continue to drive stakes.  If possible, each fence should be installed in a 6" deep trench to prevent sediment flow underneath the fence.  Make sure that all supporting posts are on the downhill side of the fencing.

Fabrijute is a flexible open weave (holes approximately ⅛" x ⅛") geotextile designed to hold seeds and soil in place until vegetation is established.  The natural looking, high strength polypropylene mesh protects the soil surface from water and wind erosion while offering partial shade and heat storage to accelerate vegetative development allowing uninhibited growth of wood plant species, grass, and ground cover.

QuickGrass is made from curled excelsior, 80% of the fibers are six inches or longer in length. Fibers expand as they come in contact with moisture. When water is released into the soil, the drying causes the fibers to contract. This process helps the fibers dig into the soil. The aspen fibers are biodegradable and add natural nutrients to the soil. The product breaks down in 9 - 12 months.

A variety of similar products (generally called Erosion Control Blankets) are also available.

Straw bales placed in small drainages act as a dam – collecting sediments from upslope and slowing the velocity of water traveling down.  Bales should be carefully placed in rows with overlapping joints (like building a brick wall).  Some excavation is necessary to ensure bales butt up tightly against one another forming a good seal.  Two rows (or walls) of bales are necessary and should be imbedded below the ground line at least six inches or held in place by stakes or rebar driven into the soil.

Straw wattles are extremely effective in controlling hillside erosion and serving as makeshift dams for blocking sediment into waterways and channels.  They are constructed of long tubes of plastic netting packed with excelsior, straw, or other material.  Wattles are used in a similar fashion to log terraces.  The wattle is flexible enough to bend to the contour of the slope.  Straw wattles last 3 - 5 years and can be left in place. 

From a recent study, the U.S. Fish & Wildlife Service reported that out of 3,300 wattles placed in a particular year, only 10 failed from storm and animal disturbance.  It was also reported that straw wattles are as effective as hand trenching, and they last much longer. 

Water bars are berms of soil or bedded logs that channel water off roads and trails to avoid the creation of gullies. Water bars are angled down the slope to the outlet side. These bars can divert water to a vegetated slope below or redirect it to a channel that will take it to a culvert. On-site soil types and the road grade will dictate spacing requirements for protecting your site. 

Water bars can only be used on abandoned roads or
where very light vehicle traffic occurs.

Log terraces provide a barrier to runoff from heavy rainstorms. Dead trees are felled, limbed, and placed on the contour perpendicular to the direction of the slope. Logs are placed in an alternating fashion so the runoff no longer has a straight down slope path to follow. The water is forced to meander back and forth between logs, reducing the velocity of the runoff, and giving water time to percolate into the soil.

Logs should be 6 - 8 inches in diameter (smaller logs can be used) and 10 - 30 feet long. The logs should be bedded into the soil for the entire log length and backfilled with soil so water cannot run underneath.  The backfill material should be tamped down.

Secure the logs from rolling by driving stakes on the downhill side. It is best to begin work at the top of the slope and work down.  It is easier to see how the water might flow by looking down on an area to better visualize the alternating spacing of the logs.

Hydroseeding is a method where wood-based fiber products are used to spray on hillsides with unstable soils.  Products of this type contain fiber mixed with a tacking agent, or binder. The liquid solution can be formulated to contain specific grass seed species so new vegetation can help stabilize the hillside.

Armoring, seeding and mulch cover have done a great job on this site.  One year after installation, a heavy vegetative mat is established and the bank should continue to be stable.