Reach 9 is a proposed Regional Flood Control Facility (channel), located in Impact Fee Service Area Number 1 (IFSA #1) in northern Sparks.  It begins at Pyramid Highway and continues east and south through new developments, to the Pioneer Meadows Detention Pond, and terminating at the Sparks Detention Basin.  The flow from the Sparks Detention Basin continues south through the IFSA #1 Regional Flood Control Facilities network of channels, Reach 11, Reach 12, and lastly Reach 12-A, until the water is conveyed in the Sparks Boulevard roadside channel to the culvert under Baring Boulevard and Sparks Boulevard intersection near Reed High School, the termination point of this analysis.

The contributing drainage area (watershed) to Reach 9, beginning at the Lemmon Valley-Golden Valley ridge line, is prone to flash flooding and substantial sedimentation.  As a vital link in the IFSA #1 Regional Flood Control network of facilities, proper sizing of stormwater infrastructure, roadway crossings (culverts), and sediment control measures along Reach 9 is paramount in maintaining flood flow capacity, forecasting Operations and Maintenance (O&M) activities and costs, and protecting properties.

The Scope of Services includes the requisite tasks to analyze historic and recent (2017) storm events to develop appropriate Regional Impact Storms for use in the modeling, analysis, and design of future stormwater infrastructure, roadway crossings, and sediment control measures for Reach 9.  The 2017 Storm Frequency Analysis will determine the actual storm (i.e., 100-year storm) that occurred and provide the basis for the level-of-service provided by the City’s existing stormwater infrastructure, based on observed flooding during this time period.  Accordingly, results of 2017 Frequency Analysis and the development of a Regional Impact Storm can serve as the foundation for the design of future critical stormwater infrastructure, stormwater master planning, and flood mitigation initiatives throughout the City.

This study will consist of 4 primary tasks that will assist the City in the design of Reach 9 stormwater infrastructure and roadway crossings, in addition to future critical stormwater infrastructure, stormwater master planning, and flood mitigation initiatives.

Task 1: Peak Flow Hydrographs Development at Key Locations

This Task includes the development of a HEC-HMS hydrologic model to determine peak flow hydrographs at key locations along Reach 9, and serve as the basis for the proper sizing design of future stormwater infrastructure and roadway crossings.  The deliverables include a HEC-HMS model, detailed hydrograph plots at all key locations requested by the City, details of parameter development, modeling methodologies, results summary tables, exhibits, tables, mapping, and support documentation.

Task 2:  2017 Storm Frequency Analysis

This Task includes the collection of available radar/gage data and conducting a statistical recurrence frequency analysis for the development of rainfall depth grids and return period contour maps for the 60-day period of record, January and February 2017, that produced flooding in Sparks. The deliverables include a statistical recurrence frequency analysis, rainfall depth grids, and return period contour maps for the 60-day period of record, January and February 2017.

Task 3: Regional Impact Storm Development

This Task includes the development of a Regional Impact Storm (RIS) for the City; a hypothetical storm event (or series of events) to be used as the precipitation input to evaluate land use changes in the City, and provide the basis for future critical stormwater infrastructure, stormwater master planning, and flood mitigation initiatives. The deliverable is a hybrid frontal-convective RIS, based on historical statistical and critical duration analysis.

Task 4: Reach 9 Sediment Transport/Accumulation Analysis

This Task includes development of a sediment transport and accumulation model for Reach 9 Regional Flood Control Channel watershed, including Sparks Detention Basin, and conveyance path through the IFSA #1 Regional Flood Control Facilities network of channels, Reach 11, Reach 12, and lastly Reach 12-A, to the culvert under Baring Boulevard and Sparks Boulevard intersection near Reed High School.  Deliverables include a sediment transport and accumulation model and analysis, Standard Project Flood Hydrograph Adjustments (SPFHAs) determined for adjusting structure sizing criteria and long-range O&M activities

1. City Council could approve the contract as outlined by Staff.
2. City Council could reject the contract and provide direction to the City Manager.

I move to approve the consulting contract as presented by staff.