Development of Numeric Flow Criteria to Support Freshwater Biological Objectives and Hydrologic Modification Management in California's Wadeable Streams

Science Center Objects

The State Water Resources Control Board (SWRCB) of California has initiated a process to develop numerical biological objectives for wadeable freshwater streams and rivers for the entire state. Use of biological endpoints for regulatory or compliance purposes requires the ability to relate specific stressors to key biological metrics and to use this understanding to influence management actions intended to improve condition or mitigate stressors. Altered hydrology is one of the primary factors affecting the health of instream communities. The importance of understanding the role of flow alteration has been recognized by the State of California and at the Federal level, within the NAWQA Program. Personnel of the California Water Science Center have been invited to join a Southern California Coastal Water Research Program (SCCWRP) assembled team to develop the metrics, statistical relations and modeling tools appropriate for aiding decisions by managers and policy makers dealing with flow alteration and biological objectives. 

Location of sampling sites for a regional monitoring program in Southern California

Location of sampling sites for a regional monitoring program in Southern California conducted by Southern California Coastal Water Research Project

For the purposes of this proposal “wadeable streams” are those where all necessary sampling activities can be completed by wading, without use of a boat, during a defined sampling period.

The basic objective of this proposal is to aid SCCWRP in accomplishing 5 tasks identified in the SCCWRP study Plan. The tasks identified for SCCWRP in the SCCWRP proposal are: 1) Convene a technical advisory committee (TAC) and develop a detailed workplan; 2) Develop a hydrologic foundation and regional stream classification system; 3) Identify and test potential flow indices; 4) Develop flow-ecology relationships; and 5) Demonstrate application of ELOHA (Ecological Limits of Hydrologic Alteration) framework to develop flow criteria. One or more watersheds will be selected to demonstrate the application of the ELOHA. With respect to participation of the CAWSC, these objectives can be restated as follows for involved CAWSC scientists:

  1. CAWSC will interact with the TAC convened by SCCWRP and will contribute to development of a detailed workplan for the SCCWRP led project;
  2. CAWSC will contribute to the development of a hydrologic foundation and regional stream classification system;
  3. CAWSC will contribute to the identification and testing of potential flow indices by critically reviewing and assessing the work of other team members;
  4. CAWSC will contribute to analysis of previously collected available bioassessment data and collect new data at approximately 40 sites with USGS flow records from active or inactive gages. The new sample sites will be representative of minimally altered flow regimes to increase the representation of such sites in the total data set. The total data set, consisting mainly of state collected bioassessment data, primarily includes data from 2 statistically designed studies with only a portion of effort applied toward minimally altered sites or from studies focused on assessing impairment. Various statistical techniques will then be used to relate the bioassessment results to selected flow indices and other selected environmental variables.
  5. CAWSC involvement with the application of ELOHA will be limited to the technical aspects of developing and applying the models (Tasks 2-4) necessary to accomplish Task 5 and by critically reviewing and assessing the work of other team members.

CAWSC scientists will participate in all tasks to various degrees. The emphasis of CAWSC staff will be Task 4, developing flow-ecology relationships. CAWSC staff will conduct field sampling at selected sites to provide critical data for the development of flow-ecology relationships. This work will emphasize watersheds with minimal alteration of the natural hydrology that are represented by current and historical USGS gages.. Further, the field sampling will emphasize the Mediterranean climate areas in Northern California and emphasize Southern California. Sampling of biology and on-site habitat measures will utilize California Department of Fish and Wildlife (CDFW) protocols to be consistent with other data being utilized in this study. A variety of data analysis techniques and modeling will be utilized to develop the flow-ecology relationships needed.

As well as addressing an important issue facing California resource managers, the project is directly relevant to the Understanding Ecosystems and Predicting Ecosystem Change component of the USGS Science Strategy. In addition, this project represents a further collaboration of the CAWSC with the NAWQA Program, SCCWRP and CDFW.