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The following descriptions of management measures to address polluted runoff are adapted from the "California Nonpoint Source Encyclopedia.”

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Follow the links below to find the subcategory of interest.

Hydromodification Management Measures:

Channelization and Channel Modification

  • Physical and Chemical Characteristics of Surface Waters
  • Instream and Riparian Habitat Restoration

Dams

  • Erosion and Sediment Control
  • Chemical and Pollutant Control
  • Protection of Surface Water Quality and Instream and Riparian Habitat

Streambank and Shoreline Erosion

  • Eroding Streambanks and Shorelines

Education/Outreach

  • Educational Programs


Hydromodification is the alteration of stream and river channels, installation of dams and water impoundments, and streambank and shoreline erosion. The management measures consist of a suite of plans, practices, technologies, operating methods, or other alternatives that may be used in combination to control nonpoint source (NPS) pollution. The seven hydromodification management measures are separated into four categories:

  1. Channelization and channel modification;
  2. Dams;
  3. Streambank and shoreline erosion; and
  4. Education and outreach.

Channelization and channel modification activities straighten, enlarge, deepen, or relocate the natural channel of rivers and streams. Channelization and channel modification activities diminish the quality of aquatic habitats and streamside habitats. These activities can alter the instream pattern of water temperature and sediment type, as well as the rate of sediment erosion, transport, and deposition. Hardening the banks of streams and rivers with shoreline stabilization protection or armor can accelerate the movement of surface water and pollutants from upstream, causing decreased water quality.

Dams can adversely impact the hydrology and quality of surface waters and riparian habitat in the rivers and streams where they are located. Impacts on surface waters and riparian habitats can result from the siting, construction, and operation of dams. Dams can reduce downstream flows affecting water quality and habitat. Construction of the dam can remove vegetation, causing increased sedimentation and turbidity. Shoreline and streambank erosion can occur after installation of a dam, which results in increased sediment load in the water body, affecting aquatic habitats.

The erosion of streambanks and shorelines is a natural process that can be beneficial as well as detrimental. Some erosion is necessary to provide sediment for beaches in estuaries and coastal bays, to provide point bars and channel deposits in rivers, and for substrate in tidal flats in wetlands. Excessively high erosion can cause sediment to smother aquatic vegetation, cover shellfish beds and tidal flats, fill in riffle pools, and contribute to increased turbidity and nutrients.

Please see the California Nonpoint Source Encyclopedia for a fact sheet on each of the management measures, containing a description of related state and federal programs, a list of specific management practices, additional information resources, example case studies in California, and references.

Link to SWRCB NPS Encyclopedia Forestry

Channelization and Channel Modification

5.1A Physical and Chemical Characteristics of Surface Waters.

  1. Evaluate the potential effects of proposed channelization and channel modification on the physical and chemical characteristics of surface waters;
  2. Plan and design channelization and channel modification to reduce undesirable impacts;
  3. Develop an operation and maintenance program for existing modified channels that includes identification and implementation of opportunities to improve the physical and chemical characteristics of surface waters in those channels.

5.1B. Instream and Riparian Habitat Restoration.

  1. Evaluate the potential effects of proposed channelization and channel modification on instream and riparian habitat;
  2. Plan and design channelization and channel modification to reduce undesirable impacts; and
  3. Develop an operation and maintenance program for existing modified channels that includes identification and implementation of opportunities to restore instream and riparian habitat in those channels.

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Dams

5.2A Erosion and Sediment Control. Reduce erosion and, to the extent practicable, retain sediment onsite during and after construction. Also, prior to land disturbance, prepare and implement an approved erosion and sediment control plan that contains erosion and sediment control provisions.

5.2B Chemical and Pollutant Control.

  1. Limit application, generation, and migration of toxic substances;
  2. Ensure the proper storage and disposal of toxic materials; and
  3. Apply nutrients at rates necessary to establish and maintain vegetation without causing significant nutrient runoff to surface waters.

5.2C Protection of Surface Water Quality and Instream and Riparian Habitat. Develop and implement a program to manage the operation and maintenance of dams that includes an assessment of

  1. surface water quality and instream and riparian habitat and potential for improvement; and
  2. significant NPS pollution problems that result from excessive surface water withdrawals.

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Streambank and Shoreline Erosion

5.3A Eroding Streambanks and Shorelines. Where streambank or shoreline erosion is a NPS problem, streambanks and shorelines should be stabilized. The use of vegetative stabilization methods is strongly preferred over the use of structural stabilization methods, if appropriate. Protect streambank and shoreline features with the potential to reduce NPS pollution. Also protect streambanks and shorelines from erosion due to uses of either the shore lands or adjacent surface waters.

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Education and Outreach

5.4A Educational Programs. Implement educational programs to provide greater understanding and awareness of watersheds, and increase the use of applicable hydromodification management measures and practices where needed. Promote projects that retain or reestablish natural hydrologic functions (e.g., channel restoration projects). Public education, outreach, and training programs should involve applicable user groups and the community.

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