Advantages of Natural Channel Design

Degraded Streams Negatively Impact Individuals

Degraded streams can negatively affect human health and property in the following ways:

• Stream bank erosion can cause damage to yards and structures built too close to a stream. Erosion can undermine trees, causing them to fall and potentially damage property.
• Excessive levels of erosion reduce water quality while areas of excessive sediment buildup may cause flooding if not routinely maintained.
• Warmed and polluted runoff can render streams unsafe for contact and fishing.
• Decreased ground water recharge can lower well water levels and produce higher concentrations of pollutants.
• Increased water volume and velocity undercuts roads, sewer systems, and storm drains, increasing costs of public services.
• Poor aesthetics of nearby waterways can decrease property values.

Through stream restoration, many of these negative impacts can be addressed and reversed.

Capital and Maintenance Benefits

Traditional Methods	NCD Methods
Lack of attention to geomorphology results in periodic maintenance to replace eroded materials or remove sediment, such as dredging	Takes into consideration sediment transport and tries to balance erosion and depositional forces so that the stream is stable over time
Channelizing the stream decreases channel stability and riparian habitat, impairs water quality and increases peak flows downstream	Provides stability and valuable riparian habitat and improves water quality
By including hard armoring to stabilize the channel, infrastructure weakens over time and needs to be replaced	Uses natural stabilization methods such as large boulders and woody structures that support vegetation and do not need to be replaced
Construction of armored structures in-stream means higher costs and erosion at transition structures	Lower initial cost and lower maintenance cost if specific criteria are met

Functional Lift

The term "functional lift" describes the process by which a stream is elevated from a degraded state to a more naturally functioning ecosystem. By restoring the natural structure of a stream, through the construction of stream features such as pools, runs, riffles and floodplains, the NCD approach enables the stream to perform additional functions.

There are five different categories of stream function that can be considered in designing a NCD restoration project: hydrology, hydraulics, geomorphology, ecology and water quality. These categories can be represented in the form of a pyramid, because the establishment of some higher stream functions requires that the foundation of lower functions be in place first. Therefore, water quality improvements to the stream are the most dependent on the establishment of lower layers in the pyramid, where hydrology is the most independent of the stream characteristics.

The NCD program design and maintenance parameters are adjustable to meet a wide range of project requirements. The level of functional lift achieved will be determined by the specific goals of each project and the project constraints. For instance, an urban flow conveyance project may be an ephemeral channel with a highly constricted right-of-way and floodplain issues. Site assessments for this project may indicate erosional issues that endanger infrastucture or sedimentation issues that impact conveyance. The NCD project goals at this site should focus on stream morphology that will stabilize the banks and balance sediment transport while maintaining or improving stormwater conveyance capacity. Pyramid Diagram and Fact Sheet © Will Harmon, Stream Mechanics. Click the pyramid image for a larger PDF.

Additional Benefits

When significant numbers of NCD projects are effectively applied in a watershed, restoration can result in cumulative ecosystem benefits, including additional storage of flood waters, removal of pollutants by plant uptake and cohesion to the soil, additional recharge of groundwater and regulation of water temperature by shading the streams from direct sun. NCD projects also provide recreational and educational opportunities, and they improve aesthetics. These values are very important to a large majority of the public but are difficult to quantify in monetary terms.