City of
Performance-Based
Operation & Maintenance
Manual
For the
Enhanced Minimum Plan
(Adaptive Management Plan)
Prepared by:
City of
(707) 967-2792
Myke Praul, City
Engineer
July December
2003
The St. Helena Comprehensive
Flood Protection Study has analyzed a number of project alternatives, which are described in the July August 2003). From this study and at this point of time,
the community has identified the Enhanced Minimum Plan as both the preferred
alternative and the environmentally superior alternative. Although the final design has
not been completed, the construction features of the Enhanced Minimum
Plan will likely include the following:
·
The creation of terraces on
the left (east) bank of the
·
The removal of under story and lower canopy
vegetation on the existing left bank terrace of the
·
Construction of a new levee/floodwall along the
right bank terrace within VVMHP and upstream to
·
The relocation of up to 33
spaces from VVMHP. The relocation of units in the VVMHP will be required
to accommodate the proposed right side terrace and floodwall. These homes will be relocated to new spaces created along and to the
north of
·
The extension of
·
Extension of Paseo Grande from
its current terminus northwest to connect with
·
Modification of the existing storm drains in
and/or along
· Construction of a levee or a floodwall to protect the operations buildings at the City Wastewater Treatment Plant. This feature will have a top elevation of 204 feet, or 5 to 6 feet above the finished grade. At this height, the floodwall will be 3 feet above the calculated 100-year water surface elevation at the treatment plant.
· Removal of existing riprap on the “point” of the west bank of VVMHP. This stretch of riverbank will likely require a bio-engineered bank protection feature.
·
Installation of large woody
debris and or rootwads as part of a streambank repair project on Sulphur Creek
at the confluence with the
·
Enhancement of the river
channel for fish passage through the
The overall goal of the maintenance and adaptive management plan is to achieve the project’s objectives after construction and well into the future.
The framework for this Adaptive Management Plan can be found in the report prepared by Swanson Hydrology
& Geomorphology entitled Geomorphic Design Report,
Many details of the construction and planting plan will be developed in subsequent engineering, design and construction phases. Meeting and maintaining conditions consistent with the project goals will require long-term monitoring, some maintenance (although it is a stated objective to minimize maintenance and have a self-sustaining ecosystem), and structural modifications to respond to changing conditions. Any proposed structural modification will involve a planning process to ensure that input of resource agencies and the community is incorporated into the design of any needed remedial measures. The Adaptive Management Plan provides the framework for this ongoing process.
An annual monitoring report will be produced to include the data, results, recommendations for any remedial actions, and proposed modifications to the project features or monitoring procedures. The monitoring team will consist of the City Engineer, a hydrologist/geomorphologist, a representative from the Department of Fish & Game, the city’ arborist and the maintenance representative of the City of St Helena. The annual report will be circulated to the appropriate resource agencies, and made available to the community and other stakeholder members for review. Annual recommendations shall be supported by a record of decision and made available for public review.
Based upon the proposed structural modifications with the EMP, the main areas of maintenance concern are as follows:
1) Vegetation planting success.
2) Topographic Changes in the Channel and
created overbank areas.
3) Hydraulic performance of the project to pass various flows, including evaluation of existing vegetation maintained annually.
4) Erosion monitoring to address problems
threatening infrastructure or properties designated for protection.
5) Aquatic and biotic resource conditions.
The objectives of a performance based O & M manual are to:
· Assess hydraulic performance of project features;
· Monitor sediment deposition and aggradations in the Project Reach.
·
Monitor streambank stability; and
·
Monitor existing and proposed vegetation for
success of riparian habitat and flood conveyance roughness coefficients; and
· Monitor the success of ecosystem restoration by documenting aquatic and other wildlife populations in the project reach over time.
The
The City has two dedicated sources of fund for Performance Monitoring and Operations and Maintenance for the
project. First, the City’s Measure A allocations
include the provision for use of Measure A proceeds during the 20-year tax and
for the funding of a Maintenance Trust Fund to be established at year 2018 to
provide for maintenance funds in perpetuity. In addition, through its
participation in the Countywide Flood Protection Maintenance Assessment
program, which taxes all parcels for maintenance of the
In order to carry out the performance-based maintenance program, various physical features that affect performance in the Project reach will be monitored to identify changes. These features are hydrology, channel geometry, vegetation, and bank stability. Not all changes are considered detrimental; considerable reconfiguration of physical features may be allowed as long as they do not adversely affect conveyance (i.e., they do not decrease freeboard more than 10-50 percent upon prior approval from FEMA), bank stability, structural integrity, or habitat quality. In fact, significant evolution of the physical features is expected to occur following construction.
Performance monitoring of the EMP has been divided into the following categories:
· Hydrology
· Hydraulic Performance
· Channel and Overbank Geometry
· Vegetation, existing and new
· Aquatic and Biotic Resources
The following sections present descriptions of design features of the EMP, monitoring methods to analyze feature performance and adaptive management measures to address potential concerns.
Basic to the design and maintenance of all flood protection
projects is the hydrology for the watershed being considered. The
In 1997, the Napa County Flood Control and Water Conservation District (FCD), in cooperation with the cities of Napa, St. Helena, Calistoga and Yountville, installed additional rainfall and streamflow monitoring equipment into what is called an ALERT monitoring system. The ALERT system supplemented the existing network of five rainfall stations and two streamflow stations installed and maintained by the USGS and DWR in cooperation with FCD. The ALERT system provides the data through radio waves, which are received at various locations within the County. The data is also collected by a consultant that provides a visual representation for the agencies and make the data available through an Internet connection for public use.
The system was installed for two primary purposes:
· Assist communities in their flood forecasting activities; and
· Provide data necessary for design and monitoring of future flood protection and environmental enhancement projects.
A key goal is to develop a data set to gain a more
thorough understanding of the hydrology of the
This data can now be used to estimate the flow for each storm that occurs in the watershed and then correlated to the visual conditions through the reach of the EMP. As discussed in the following section on Hydraulic Performance, this correlation will be important in analyzing the performance of project features compared to project objectives. The analysis will assist in identifying potential areas of concern that can lead to preventive maintenance measures.
The ALERT system requires annual and periodic maintenance to
assure proper performance and accuracy.
The City of
II. Hydraulic
Performance
Based upon the hydrologic data collected in paragraph I above, the hydraulic performance of project features over a range of flows can be analyzed and evaluated for hydraulic performance. Actual hydraulic performance helps account for a complex set of assumptions that have to be made in project design and modeling. The range of flows of interest includes large floods up to 100-year peak design flow down to the 500 cfs range to assess geomorphic processes in and around the low flow channel. Hydrologic data provided by the ALERT system will be valuable in analyzing the hydraulic performance of the EMP.
Maintain as close to a 100-year flood capacity, with an
additional three feet of freeboard, in the project reach of the
Flow levels will be monitored by several methods in order to evaluate hydraulic performance. The effort will be geared toward developing a reliable hydraulic model of the project in order to compare predicted modeling with actual performance results. Integration of hydraulic performance monitoring with the topographic surveys and vegetation cover is an essential requirement.
Within the project a set of water level recorders and crest gages will be established under consultation with MBK Engineers and David Ford Consulting Engineers. These devices will allow for continuous water surface measurements and peak water stages at various locations in the project reach. These devices should be supplemented with field high watermark surveys after known floods or during actual flows when conditions allow for safe access.
The data collection frequency should be intensive just
after construction in order to establish water surface / discharge relations
over a range of flows in the channel, at the inlets of overflow channels and in
the overbank areas. As data is compiled, levels will
be monitored to see if flood capacity objectives are being met and if any topographic
changes are creating problems.
Measures have been taken during project design to
create a self-maintaining project that after the initial vegetation
establishment period, will require little if any
maintenance. However, Ppotential concerns would
arise if the flood capacity is reduced below the
design level or if geomorphic stability is compromised. These problems could
occur due to sediment deposition, erosion, topographic changes,
higher than expected hydraulic roughness, or differences between actual flow
capacity and hydraulic modeling predictions.
A thorough alternative assessment should be undertaken if in the unlikely event flood capacity is reduced below the design level or geomorphic stability is compromised and changes are necessary, such as removal of sediment or vegetation or increasing the height of levees or floodwalls. The project has been designed to include 3 feet of freeboard on levees and floodwalls above calculated 100-year peak flood water surface elevations; this must be maintained to retain FEMA certification. Vegetation shall not be disturbed or removed any more than necessary to maintain the flood protection goals of the project. If it is determined that the capacity for the design 100-peak year flood protection goal has not been met, a range of options should be assessed, including a no-action plan to accept a lower flood capacity.
Other measures might be taken if hydraulic performance does not produce anticipated ecological benefits. This might include regrading and revegetating areas where conditions have not resulted in successful plantings, for example. Or there may be a need to reduce or increase the frequency of overbank flow. Resource agencies would be consulted and required permits/approvals obtained prior to implementation of any of these measures. The annual inspections will be correlated with the hydrological data to analyze potential modifications to construction features of the EMP.
III. Channel
and Overbank Geometry
Much of the project success will depend upon maintenance of the project area topography within an acceptable range of elevations to achieve flood capacity objective of containment of a 100-year flood. Topography will dictate flood capacity to a great extent and can be an influence on geomorphic stability and processes.
The nature of deposited sediments is of great interest to many aspects of the project, including sediment deposition as it affects flood capacity, mineral soils for native plant colonization, etc. The size of bedload transport deposited in the channel will help determine the quality of aquatic habitat and whether there is a trend in bedload deposits that might bear upon channel stability.
Monitoring and management of erosion problems is an
important component of the adaptive management plan. It is anticipated that the
Goals
Maintain slope ratios from the base of floodwalls, levees
or the designated edges of properties and infrastructure as selected during
final design to the extent possible.
Topographic cross sections will be established across the project site after construction. An as-built topographic survey shall document post-construction topography. The density of the cross sections should be adequate to construct a hydraulic model, or approximately one cross-section every 300 feet, and should extend from the edges of the flood plain through the channel. River cross sections currently identified as critical for the monitoring the performance of the EMP will be labeled upon final design and include:
·
The
· The gravel bar in the river at the confluence with Sulphur Creek
· The “point” in the area of the existing riprap
· The outlets to the east and west overflow channels
· The inlets to the east and west overflow channels
·
The
The baseline survey will be used to construct a hydraulic model of the project in conjunction with the hydraulic roughness data input from the vegetation surveys. The cross sections will be surveyed annually until it is deemed by the City and in consultation with resource agencies that less frequency is required. There should be a focus on surveys after major flood events (greater than 10-year peak flow) when topographic changes might be greatest.
Just after construction and once every five years a full topographic survey of the project site will be undertaken using a combination of ground surveys (in areas covered by vegetation) and aerial surveys. A 2-foot contour interval should be adequate in most open areas. The aerial should have an underlying ortho-rectified color aerial photograph. The City will also assess frequency of this monitoring after the first five-year interval.
A field survey of the longitudinal profile of the channel will be measured every five years after construction. Upon completion of the ten-year survey, the
City will assessed the necessity for future
surveys. The longitudinal profile will
measure streambed thalweg, water surface, bankfull features, and any high water
lines. The data will be managed for assessment by the
project geomorphologist for an annual review and presentation.
Sediment data will be collected in the channel and on the flood plain surfaces using standard pebble count and surface sampling collecting methods. Channel sampling should include pebble counts in the channel in a consistent geomorphic location, sampling of sub-surface layers below the channel bed, and sampling of newly deposited sediments on the banks (i.e. bankfull sediments). The samples should be analyzed for grain sizes and the sample locations mapped.
Sediment deposits in flood plain areas will be mapped and sampled. The fresh deposits will be mapped annually on the most recent aerial photographs and will include the lateral extent of the deposit as well as the depth. A sample will be taken of selected deposits for grain size analysis.
The channel and designated erosional limit areas will be inspected annually for any problems, such as
new or progressing erosion that could potentially progress into an established
“no erosion” zone. The inspections will be visual, but will also
include examination of aerial photos and topographic surveys in order to
determine any trends.
The topographic cross sections and maps will be compared by a geomorphologist with previous surveys in order to assess changes and make recommendations, if necessary. The key areas of concern are: aggradation of the channel with coarse bedload to a degree that could impair flood capacity (see hydraulic performance above) or channel stability and aggradation of the overbank flood channels or created flood plain. The monitoring data will also reveal problems with full spanning logjams that inhibit fish passage or might pose a threat to lateral channel stability. The project geomorphologist should make recommendations to rectify any problems in consultation with the City and appropriate agencies.
It is anticipated that the EMP project will actually reduce erosional forces along the channel rather than increase the hazards. Subsurface explorations have revealed that the soils are relatively cohesive and strong and able to hold steep slopes. They also erode slowly, which may partially explain the long-term stability. However, erosion must be taken seriously as a future project maintenance issue.
The process for addressing erosion problems will be highly proactive under the adaptive management plan. First, the monitoring program will reveal potential problems early so that low-tech, vegetative methods will be employed to slow down or eliminate erosion. If the problem(s) become severe enough to warrant structural treatment, then a design process will be initiated.
The design process will include identification of a range
of treatment options emphasizing bioengineered methods to create opportunities
for habitat development. The proposed alternatives would be
made available to resource agencies and the City for consideration and
selection of a preferred plan. TAgain, the emphasis will
be to treat erosion problems as early as possible with vegetative techniques to
minimize any need for the cost and potential effects of structural bank
protection.
An example of a bank protection alternatives document has recently been completed for a location at the confluence
of Sulphur Creek and the Napa
River where a failure
occurred in 1998. This site is being considered for
repair prior to construction of the floodwall included in the EMP. The
alternative plans range from no action to full revetment with several different
options in between. The report describing these options is included as Appendix
C to the revised draft EIR.
The vegetation planting component is a key element of the project as it is anticipated to provide soil and channel stability and habitat value. The specific objective is to achieve the vegetation cover shown on the planting plan presented in the revised draft EIR. It may become necessary to modify the plan during the design and engineering phase and perhaps during project life if post-project conditions are different than those anticipated in the original design. The following monitoring and maintenance plan is designed to collect the data necessary to determine if success is being achieved and if adjustments are necessary.
Monitoring
The initial 5-year establishment period will involve intensive efforts to establish native plantings and to have native plantings out-compete undesirable invasive non-natives (i.e. arundo donax, etc.). A specific revegetation plan will be prepared for construction with the details of design, planting species, densities, irrigation and performance. Carrying out the revegetation plan will be the responsibility of the landscape contractor; however it will be important to ensure that it is directed to meet ecosystem and EMP goals.
Goals
Maintain vegetation in the terraces according to the Vegetation Establishment Plan that 1) meets the roughness criteria needed to provide as close to 100-year flood protection as possible, 2) stabilizes soils, and 3) provides suitable habitat for target species in the project reach.
Monitoring
Prior to construction, vegetation transects will be established to measure pre-project conditions. These will be used to compare future post-project conditions. After construction and during the establishment period, the monitoring transects will be established at the same locations as the pre-project locations and will coincide with some of the topographic cross sections (described above) and shallow groundwater monitoring wells. The groundwater wells will be arrayed along three selected cross sections to document the gradient of water levels in the plant rooting zones.
Annual surveys of plant communities will be measured to document plant development, species composition and diversity. There are several methods for developing annual plant databases in a statistically meaningful way.
The overall plant cover will be mapped by plant community cover type every two years using the most current color photographic survey. This will allow for collection of time-sequenced data that can be incorporated into a GIS database for quantitative comparison to the original plan. The survey will also serve to develop a biannual maintenance plan to replace failed plantings, to tag areas for removing exotic vegetation, or other actions. The survey should be conducted at least twice in the first five years as part of the landscape installation contract and, thereafter, as often as it is deemed appropriate to properly monitor the plantings.
Based upon the monitoring results, the project vegetation specialist may determine that modifications to the original revegetation plans are in order due to different or changing conditions. For example, there may be natural native plant colonization that occurs that is different than prescribed by the planting plan. Or there might be areas subject to frequent scour or too dry to support the intended vegetation cover. The vegetation specialist should propose a modified cover that complies with flood capacity objectives and the goals set by the regulatory agencies.
A key component of the EMP
project is to achieve significant ecosystem restoration for the project reach and
avoid impacts to wildlife during operation of the project. The
success of the project will be assessed through direct
measurement of wildlife populations and habitat usage.
Maintain and enhance wildlife
populations, including special status species, in the project reach of
The success of the project will be assessed through direct measurement of wildlife populations and habitat usage. Standard wildlife habitat survey methods will be employed the project wildlife biologist to document pre- and post-project wildlife populations. The methods include visual surveys of birds, aquatic, terrestrial and amphibious wildlife and trapping for species that provide food for higher mammals and raptors. Surveys for aquatic species include diving and electroshock population surveys for fish and sampling of aquatic insects. A specific set of objectives for wildlife populations (more specific than “maximizing”) will be established after the baseline survey of existing resources and examination of the final EMP project. The same methods for monitoring surveys will be used during annual inspections.
After flood events the City will monitor the terraces to check for
stranding of fish and other impacts to wildlife.
Post-flooding,
Wwildlife population surveys alongside and
plant surveys will be used as a tool to measure the
success of ecosystem restoration and of avoiding impacts to wildlife during
project operation. The wildlife biologist(s) shall make recommendations for the
improvement of the ecosystems and the avoidance of operational impacts on
wildlife within the project area based on survey results. The potential measures that
will be employed to enhance wildlife population include removal of exotic
species and predators (e.g. cowbirds and feral cats), installation of nesting
boxes, modification of plant communities or topography to favor habitat for
selected species, management of woody debris in on the sides of the
channel to favor development of desired aquatic habitat, or manipulation to
improve amphibian habitat. If
impacts to wildlife occur during flooding events, design modifications to the
terraces and/or appropriate response methods may be considered.
SUMMARY OF ADAPTIVE MANAGEMENT PLAN
This draft Adaptive Management Plan is a performance-based operation and maintenance manual for the Enhanced Minimum Plan as presented in the St. Helena Comprehensive Flood Study. Its finalization will occur after:
· Certification of the final EIR
· Selection of a project by the City Council
· Design of that project
· Construction of the project
It will be prepared in consultation with Regional Water
Quality Control Board, the United State Army Corps of Engineers, Department of
Fish and
The following table is presented as a summary of this plan to date that will serve the City as a checklist of periodic monitoring and maintenance activities.