5.1 – Stream Channel Modification

• 5.1A – Channelization/Channel Modification
• 5.1B – Dams & Levees, Construction
• 5.1C – Dams & Levees, Operation and Maintenance
• 5.1D – Dams & Levees, Removal

5.2 – Managing Hydromodification Impacts

• 5.2A – Streambank & Shoreline Erosion Control
• 5.2B – Flow & Temperature Maintenance

5.3 – Education & Outreach

• 5.3 – Education & Outreach for Hydromodification

Hydromodification (i.e., stream channel modification) is the alteration of stream and river channels resulting from activities such as:

• Construction and maintenance of channels, levees, dams, and other water conveyance structures and/or impoundments for purposes of flood control, water storage, water conveyance, and navigation;
• Dredging and/or filling or other alterations to natural land contours for the purposes of new development (including transportation and other infrastructure) or navigation;
• Development that increases runoff volume and/or velocity (flow rate), or alters the timing of runoff flows; this includes construction of impervious surfaces (such as asphalt, concrete, and buildings), and deforestation or removal of vegetation.

Hydromodification can result in adverse impacts on the physical and chemical characteristics of surface waters, on groundwater levels, and on aquatic and riparian habitat. Hydromodification effectively reduces stream base-flow (i.e., groundwater flow into streams) and increases overland or storm-flow, which causes reduced groundwater recharge and increased peak runoff discharge rates into streams and rivers. Hydromodification may result in stream channel instability and streambank or shoreline erosion, which in turn modifies the stream’s natural water temperatures and flow regime.

Descriptions of this land use category and its Management Measures are adapted from California’s NPS Encyclopedia. More Info