EXHIBIT 4-A

 

Project 1 – Update of the Canyon Del Rey Master Drainage Plan

 

SUMMARY

Canyon Del Rey Creek is an ephemeral stream that drains to the Pacific Ocean; the watershed includes portions of Seaside, Del Rey Oaks, Monterey, and unincorporated Monterey County.  The Monterey County Flood Control and Water Conservation District (since renamed the Monterey County Water Resources Agency or MCWRA) completed a Master Drainage Plan for the watershed in June 1977.  The plan included a hydrologic analysis of existing data, predictions of future flows, a hydraulic analysis of existing facilities, and made recommendations for future improvements.  No update of the plan has occurred since completion of the study.  Since that time, significant development has occurred, General Plans for cities and unincorporated areas have changed, water quality standards for stormwater runoff have increased, and tools to understand and predict water and sediment flows have improved. 

 

This update is a cooperative effort between MCWRA, the City of Seaside, and the Monterey Peninsula Water Management District (MPWMD), all of whom will take the lead in the development of a final scope of work for the consulting Request for Proposals, review work products, and provide in-kind services and funds.  Other contributing agencies include the City of Monterey and the Monterey Peninsula Regional Park District. 

 

It is expected that one or more consultants will be retained to complete the work.  Consultants will have the responsibility for developing Quality Assurance Project Plans that meet all applicable statewide database standards, and for modifying them in response to comments.  A high level of consultant qualifications may be required to carry out the drainage plan update.  [1]

 

Task 1:  Update of the Hydrologic Model

In this task, the consultant will assess existing conditions in the Canyon Del Rey watershed (e.g., land use, drainage condition) and compare existing conditions with those assumed in the 1977 Canyon Del Rey Creek Master Drainage Study for future conditions.

 

Subtask 1.1    Watershed Characterization

  1. Identify and document changes in land use and drainage facilities/structures that have occurred in the watershed between 1977 and the present, using aerial photographs to determine the percent of impervious area and, if feasible, identify significant detention and/or retention facilities that might affect runoff. 
  2. Contact local land use jurisdictions and ask for copies of updated land use maps, facilities maps, or other information that would contribute to understanding changes in land use and/or drainage patterns.

 

Subtask 1.2                Watershed Evaluation

  1. Field Evaluation – using information from Subtask 1.1, a field survey of selected facilities will be conducted to assess and document areas of potential problems.  If possible, problem facilities would be observed during rain events.  Note: this may be part of Task 3.1. 
  2. Report Evaluation – where annual reports or other documents about drainage facilities are available, information about the effectiveness of a facility will be used.  The Consultant will also review the 1977 breakdown of the watershed into sub-watersheds.  If appropriate, a new set of sub-watersheds may be developed for additional analysis in Task 2.
  3. A map of the identified areas will be prepared, and the results of this subtask will be used in other tasks described below.

 

Subtask 1.3    Update Precipitation Estimates

  1. Prepare updated estimate of rainfall rates using acceptable data from local rainfall reporting stations and developing updated isohyetal maps and actual or correlated annual rainfall totals for the period of record.  Where appropriate, rainfall data and analyses from nearby watersheds may be used for comparison. 
  2. Correlate daily records for about 8 stations over 60 to 70 years, plus depth/duration/frequency tables for 3 stations with most-complete records.

Task 1 Deliverables: Report or memo with a summary of information examined, appropriate documentation of field verifications (notes, maps, photographs, survey information); updated map showing sub-watersheds; updated isohyetal maps for the watershed; depth-duration-frequency tables and graphs for the 2, 10, 100, and 500-year events at stations with the most complete records.  

 

Task 2:  Update Runoff Estimates

 

Subtask 2.1    Evaluate Appropriate Runoff Estimation Methods

The 1977 plan used the synthetic unit hydrograph.  There are several alternate methods currently available for evaluating runoff. 

  1. The Consultant will evaluate existing methods and in consultation with agency staff, recommend a method to estimate flows in the basin and sub-watersheds.

Subtask 2.2    Estimate Existing and Future Flows

  1. The Consultant will develop an estimate of present and future flows at critical locations along the creek and in sub-watersheds.  Flow predictions will be on intervals for use in standardized models to evaluate flooding (e.g., HEC-RAS) and stormwater runoff (e.g., SWMM).  Basin characteristics for a future developed condition will be based on approved General Plans in the cities and unincorporated Monterey County areas.

It should be noted that information from Tasks 3 and 4 may be required in order to make flow determinations.

Task 2 Deliverables:  A table of existing and future flow conditions for the 2, 10, 100, and 500-year recurrence interval at critical locations along the creek and in sub-watersheds identified in sub-task 1.2.

 

Task 3:  Evaluate the effectiveness of the primary drainage facilities in the watershed

 

Subtask 3.1    Determine the existing condition of primary facilities

The 1977 study recommended improvements to 19 primary drainage facilities. 

  1. Verify the size and condition of each facility, using City and County records and field visits. 
  2. Inspect drainage facility no. 46, which is a quadruple 6 ft. by 6 ft. by 750 feet long reinforced concrete box (RCB) outfall from Roberts Lake that goes under Highway 1.

Subtask 3.2    Bathymetric study

  1. Conduct a bathymetric study of the lakes, and sample sediments;
  2. Provide report from the sediment analysis to local agencies interested in the beneficial use of material dredged from the lakes to replenish sands at local beaches.

Subtask 3.3    Determine whether existing facilities are adequate

  1. Evaluate the effectiveness of each facility to pass flows using information provided from previous tasks; 
  2. The Consultant will make recommendations to improve the facilities or make recommendations for additional work, where facilities are found to be inadequate.

 

Task 3 Deliverables: A summary of the condition of primary facilities that includes photographs and field data; results of bathymetric surveys (stage-volume data); results of sediment analysis; conclusions and recommendations for additional work.

 

Task 4:  Project Management

This task consists of standard project management, including scheduling, budget tracking, invoicing, and general project communications.  Also included in this task are regular communications with agency staff, conference calls as required, and quarterly progress reporting.

 

Task 4 Deliverables:  Invoices; quarterly progress reports; copies of communications among agencies and consultants (if appropriate).

 

Optional Tasks if Funding is Available

 

Task 5:  Update of erosion and sedimentation rates in the tributaries, main stem and in Laguna Grand and Roberts Lake

Subtask 5.1    Evaluate erosion and sedimentation data

Obtain answers to the following questions:

1)  What are the past, present, and expected future sediment loads from the watershed?

2)  Where are the sources of sediment? 

3)  Are the drainage facilities for new developments that have been required since the 1977 drainage plan was completed functioning as intended? 

Subtask 5.1.1 Historical analysis

The consultant will review historical data of erosion rates in the watershed and sedimentation at Laguna Grande and Roberts Lake.  This includes a review of the effect of dredging projects at the lakes and any other information of the sediment loading and changes in the rate of loading from the watershed.  As part of this review, past City of Seaside officials and others who may have been involved with managing the lakes will be interviewed and documentation sought about past management efforts. 

Subtask 5.1.2 Sedimentological Study

From Subtask 3.2, obtain sediment samples from the lakes, and provide a report from the sediment analysis to local agencies interested in the potential for beneficial use of any material dredged from the lakes to replenish sands that are being lost from local beaches.  Additionally, sediment samples from other parts of the watershed may be obtained and analyzed in an effort to establish their original source based on mineralogical or lithological evidence.

 

Task 5 Deliverables: If, after receiving Requests for Proposals, and in consultation with the Department of Water Resources, it is determined that funds are available for the optional tasks described in Task 5 above, the final scope of work may include additional deliverable items including  sediment loading data from the watershed and the results of an investigation of sediment sources.

 

 

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[1] These may  include, where appropriate, (a)  conformance with State of California professional registration requirements as professional engineers, geologists, and (optionally) advanced certifications such as geotechnical engineer, engineering geologist, or certified hydrogeologist, (b) prior experience with the hydrologic models proposed, (c) evidence of experience with  stream gaging or suspended-sediment and bedload-sediment sampling, and (d) submittal of prior sediment-quality sampling and testing-protocol development.