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Table of Contents >>  4.3 Forest Management in Riparian Areas << 4.4 Stream Crossings and Habitat >> Forest Health: Additional Reading



Roads are necessary for forest management and access for outdoor activities such as hunting, fishing, hiking, wildlife watching and snowmobiling. Roads that cross streams can impact stream habitat and streamflow.

This chapter addresses the needs of fish and other aquatic organisms. The importance of intermittent streams is also addressed. Best management practices (BMPs) to prevent erosion can be found in Best Management Practices for Erosion Control on Timber Harvesting Operations in New Hampshire published by the N.H. Dept. of Resources and Economic Development, Division of Forests and Lands. You can learn about additional practices in Best Management Practices for Forestry: Protecting New Hampshire's Water Quality. Using BMPs minimizes the impact of crossings on streams and stream habitat during timber harvesting.

Aquatic organisms move upstream and downstream throughout their life cycles. The survival of a population depends on access to spawning habitat, feeding areas, and shelter, as well as the dispersal and colonization of available habitat by juveniles.A healthy population also depends on unrestricted gene flow; crossings may isolate populations, making them vulnerable to extirpation. Many species of amphibians, reptiles, and mammals use riparian zones as travel corridors, and their movement may be impeded by certain crossings.

Instream wood (trees and branches), sediment, and ice transport are important. Trunks and branches (1) retain nutrients within the stream and keep excess nutrients from going into waterbodies downstream, (2) create pools for fish and other aquatic animals, and (3) are used by fish as refuges to avoid predators and high water velocities that occur during floods. Downed trees are a natural component of streams, and they are often transported long distances from where they initially entered the stream channel. It's important not to create conditions that cause downed wood from upstream to block the stream crossing. Sediment and ice are also integral parts of stream systems; like branches they can plug undersized stream crossings. Erosion can cause an increase in nutrients, reducing water quality, especially in downstream waterbodies (4.3 Forest Management in Riparian Areas).

These same processes occur in intermittent streams and perennial (year-round) streams. The surrounding forest provides leaves and coarse woody material critical to the food web along the entire stream course. These materials are carried downstream, as are the invertebrates that feed on them. Crossings on intermittent streams should also allow for aquatic organism passage, since aquatic invertebrates, some unique to intermittent streams, occupy these streams year-round.

The following is a brief discussion of the more common types of crossings most often used in timber harvesting operations:


Bridges span streams entirely, and can be the best way to protect the stream and crossing structure. They can be permanent or temporary and made of wood, metal or a combination. Permanent bridges are often used for truck roads, while temporary bridges may be used for skid trails. Sited properly, bridges won't affect water flow and will reduce or eliminate erosion of the bank. Improperly constructed abutments can cause bank erosion.


A culvert is a corrugated pipe, well-casing, or other type of pipe placed under a truck road or a major skid trail to permit the crossing of an intermittent or perennial stream. A culvert can be either temporary or permanent. (Culverts used as cross-drainage in truck roads aren't covered in this chapter). In general, culverts installed within truck roads are permanent crossings.

An improperly designed, sized, or installed culvert can block fish, other animals and natural materials from moving downstream. Culverts can lead to streambed and bank erosion on the downstream side of the culvert due to the increased water velocities exiting the pipe. The result is a perched culvert with its downstream end above the water. The resulting waterfall can prevent aquatic animal passage.

Poled Fords

A poled ford is a temporary stream crossing in which natural materials are used to fill a defined channel to allow for the passage of vehicles. Per RSA 482-A, poled fords are a BMP and must be removed as soon as the site is closed. Leaving them in place after the permit expires is considered fill and violation of state law. Leaving them in place can also lead to streambed and bank erosion and reduced aquatic animal passage. Corduroy (poles, logs or brush laid perpendicular to the direction of travel), used to fill wet places that aren't streams, aren't considered poled fords and may be left in place.

Stone Ford

Stone fords use the stable stream bottom or stone fill as the road bed. They are intended as permanent crossings since their removal can cause erosion and turbidity. On roads where the wide width and shallow water combine to make a bridge or culvert unworkable, a stone ford combined with a culvert sized to accommodate fish and other aquatic organism passage is an option.


Provide safe stream crossings that allow passage of aquatic animals up and down the stream and protect water quality.




4.1 Water Quality; 4.2 Wetlands; 4.3 Forest Management in Riparian Areas.


N.H. Administrative Rules Env-Wt 900. http://des.nh.gov/organization/commissioner/legal/rulemaking/documents/env-wt900adpt-pstd.pdf Accessed June 1, 2010.

N.H. Dept. of Resources and Economic Development, Division of Forests and Lands. 2004. Best Management Practices for Erosion Control on Timber Harvesting Operations in New Hampshire. State of New Hampshire. http://extension.unh.edu/resources/files/Resource000247_Rep266.pdf Accessed March 13, 2010.

RSA 482-A. Fill and Dredge in Wetlands. http://www.gencourt.state.nh.us/rsa/html/l/482-a/482-a-mrg.htm Accessed May 27, 2010.

Smith, S. (ed). 2005. Best Management Practices for Forestry: Protecting New Hampshire’s Water Quality. UNH Cooperative Extension, Durham N.H. http://extension.unh.edu/resources/representation/Resource000248_Rep267.pdf Accessed February 8, 2010.

Smith, S. 2009. Guide to New Hampshire Timber Harvesting Laws. UNH Cooperative Extension, Durham, N.H. 37 p.

US Geological Survey. NH StreamStats. http://water.usgs.gov/osw/streamstats/new_hampshire.html Accessed February 8, 2010.

Vermont Division of Forestry. 2008. Wooden Portable Skidder Bridge Information Sheet. http://www.vtfpr.org/watershed/portbridgebroc.cfm Accessed on January 21, 2009.

4.3 Forest Management in Riparian Areas << 4.4 Stream Crossings and Habitat >> Forest Health: Additional Reading

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