Data and Analysis Requirements for Small Dam Removal

Data and Analysis Requirements:
Minimal and Potential Data Needs: Listed below are the minimal and potential data needs for conducting any small dam removal project. However, site specific conditions may require additional information beyond what is identified here to adequately evaluate a small dam removal project. Similarly, unanticipated complications in a project such as the need to use a roughened channel and/or other fish passage techniques to pass fish over buried infrastructure (e.g., gas, water, and sewer lines) will require additional data. The minimal data needed to conduct simpler small dam projects along with the potential data needs for more complex projects is listed in the project description section (to read project description refer to SDM-001) .
1) Minimal Data Needs:
A) A clear statement of the fish passage objectives of the project.Objectives shall be explicitly stated for any small dam removal project (e.g., to improve fish passage, improve sediment continuity and downstream spawning habitat, and/or to provide passage meeting specific fish passage guidelines).
B) A clear statement and justification for the project’s method of restoring the channel along with a sediment management plan.
C) The proposed time-frame for dam and sediment removal along with the time expected for channel equilibrium to occur at the project site. Include anticipated and actual start and end dates of project.
D) The distance and location of nearest upstream grade control feature (natural or anthropogenic).
E) An estimate of depth and volume of sediment stored above the dam. Evidence that the amount of sediment to be released above the dam is relatively small and unlikely to significantly affect downstream spawning, rearing, and/or over-summering habitats. The estimate should be determined with a minimum of five cross-sections – one downstream of the structure, three through the reservoir area upstream of the structure, and one upstream of the reservoir area outside of the influence of the structure – to characterize the channel morphology and quantify the stored sediment.
F) Detailed information on project/reference reach including:
1. Location of project/reference reach.
2. Channel width (baseline and target range in feet): Should be determined by taking three measurements of active channel at the dam and immediately upstream and downstream of the dam.
3. Any existing geomorphic features present and that will be incorporated into the channel (e.g. pools, riffles, runs, step-pools, etc.).
4. Overall channel slope (% baseline and target): determined by taking a longitudinal profile throughout the project reach upstream and downstream to the extent of dam influence on the channel slope.
5. Maximum channel slope: determined through the site before and after the project using pre-project and as-built (post-project) longitudinal profiles.
6. Photographs of pre and post project conditions, illustrating implementation of the dam removal, upstream sediment deposit/reservoir, and channel morphology upstream and downstream of the proposed project reach.
7. Maximum jump height (baseline and target range in inches): using the pre-project and/or as built longitudinal profile to determine the maximum height a fish would have to jump to migrate through the site.
8. A longitudinal profile of the stream channel thalweg for at least 20 channel widths upstream and downstream (pre and post project) of the structure or of a sufficient distance to establish the natural channel grade, whichever is greater, shall be used to determine the potential for channel degradation (as described in the CDFW Manual).
9. The number of stream miles opened by each project should be estimated before implementation and verified after project completion. The following sources may be used to verify the number of upstream miles made accessible as a result of the project: exiting aerial photos and maps of the project watershed, local or regional barrier databases, existing staff or local expert knowledge of project watershed, and/or field verification (in cases where there is permission to access the stream).
10. A survey of any downstream spawning areas that may be negatively affected by sediment released by removal of the dam.
11. Presence/absence of salmonids:
Pre-implementation: Use one of the following survey techniques defined in California Coastal Salmonid Population Monitoring: Strategy, Design, and Methods (Adams et al. 2011) to identify and report presence/absence for either adults or juveniles upstream of
the project site. Describe the survey techniques used to determine presence/absence status of salmonids. If a pre-implementation survey is not possible, report whether the barrier is a known full barrier or partial barrier for salmonids. Describe any pre-project
data that is available. If no recent, biological information is available, include surrogate information (e.g. most recent observation of species above barrier, description of “completeness” of barrier, etc.).
Post-implementation: If the pre-implementation status was determined to be “absent,” use one of the survey techniques to identify and report presence/absence following implementation. If pre-project upstream status was determined to be “present” (e.g.
partial barriers), report any change in presence/absence following implementation if possible. In this case, the post-implementation result may be “continued presence.” Describe the methodology used to determine presence/absence for the target fish species.
Frequency /duration of sampling: The timing and frequency should correlate with the life history of the target fish species. At a minimum, if landowner access is allowed, this parameter should be monitored one time following implementation, and if funding and
landowner access allows, would preferably be monitored on an annual or seasonal basis. Monitoring for this measure is likely to yield meaningful results in the first 3 years after project implementation, although in some situations it may be valuable to monitor for the first 5 years. Optional monitoring: for partial barriers or projects where the pre-implementation fish presence/absence status was identified as “present,” the proportional change in the number of adults or juveniles due to project implementation may be measured.
2) Potential data needs for more complex projects:NMFS engineers and/or the RC lead may request additional information from more complex projects to include:
A) Hydraulic modeling immediately upstream and downstream of the project site, and throughout the project reach.
B) Sediment modeling immediately upstream and downstream of the project site, and throughout the reach of the stream in which the project is located, including: Sediment grain size distribution within the dam depositional area and the sediment grain size distributions of the channel bed material within the equilibrium reaches upstream and downstream of the dam; recurrence interval of the discharge needed to mobilize the sediment particles and any established vegetation within the sediment deposit upstream of the dam that is to be removed; and bed and bank grain size distributions.
C) Detailed geomorphic assessment of the watershed and/or stream reach.
D) Detailed hydrologic analysis of the watershed and how it will drive the geomorphic conditions within the watershed before and after dam removal.
E) A detailed assessment of the habitat conditions within the watershed and/or upstream and downstream of the reach of the stream in which the project is located.
e. Two conditions that may preclude a project from eligibility for coverage under the Program are: 1) if sediments stored behind dam have a reasonable potential to contain environmental contaminants (may include but not limited to: dioxins, chlorinated pesticides, polychlorinated biphenyls (PCBs), or mercury) beyond the freshwater probable effect levels (PELs) summarized in the NOAA Screening Quick Reference Table guidelines found at: http://response.restoration.noaa.gov/book_shelf/122_NEW-SQuiRTs.pdf, or 2) if the risk of significant loss or degradation of downstream spawning or rearing areas by sediment deposition is considered to be such that the project requires more detailed analysis. Sites should be considered to have a reasonable potential to contain contaminants of concern if they are downstream of historical contamination sources such as industrial sites, or sites where intensive agricultural production going back several decades occurred (since chlorinated pesticides were legal to purchase and use for many years). In these cases, preliminary sediment sampling is advisable for a project to be considered for coverage under the proposed Program.