Watershed and Wallet Friendly Roads

Improving Water Quality While Reducing Road Maintenance Costs

Storm-proofing road systems can have an immediate benefit to the streams and aquatic habitat as well as protect the road surface and reduce annual road maintenance costs. The practices recommended below help ensure that stream habitat is not impacted by human-related road erosion. If storm-proofing treatments are implemented correctly, future storm runoff can cleanse the streams of accumulated coarse and fine sediment rather than deposit fine sediments in areas where it impairs aquatic habitat.


Poorly constructed roads have potential to create flashier streams and increase sediment delivery to streams from chronic erosion and episodic erosion events:

Roads Create Flashier Streams 

  • Poorly constructed roads collect and concentrate surface stormwater flows from the landscape 

  • Concentrated flow from the road network enters the stream system with greater volume and velocity than what the stream would normall experience. The increased energy of the water causes the stream channel to incise, which may ultimately lead to bank erosion and lowering of the water table

  • Since roads collect and channel water moving across the surface, less water ends up recharging the groundwater basin, which decreases summertime stream flows and leads to drier soils downhill of the road

When roads collect, concentrate, and deliver runoff to streams they create flashier stream flows

Roads Increase Chronic Erosion and Sediment Delivery

  • Roadways and road-side ditches accumulate fine sediments during the dry season

  • During most storms, as water flows across the road surfaces and ditches, it picks up the accumulated fine sediments and can eventually deliver them directly to the stream system

  • Erosion and sediment delivery occurs during every storm that produces runoff; it's a chronic process

  • Unpaved roads contribute more sediment to streams via chronic erosion than paved roads because they have much more erodible surface area 

Chronic sediment delivery occurs when road surface drainage is constantly eroding the road or ditch surface and is connected to a stream

Roads Increase Episodic Erosion and Sediment Delivery

  • Large storm events, earthquakes, and other factors can create large scale erosion events that end up resulting in large pulses of sediment being delivered to streams

  • This type of erosion is episodic, it occurs in pulses and not at a constant or predictable rate

  • Example: Steep cutbanks associated with roads may fail in response to storm events or other triggers, such as earthquakes

  • Example: Stream crossings may flood and washout during floods

  • Example: Flooded roads may produce gullies in the fill slope

When culverts flood, due to plugging or improper sizing, large amounts of sediment near the stream crossing is vulnerable to erosion and delivery to streams


Visit this page to get more information about designing and maintaining roads in order to minimize erosion.