The 2011 City of Sparks Stormwater Basin Masterplan identified the area of East Prater Way and Vista Boulevard as an area that required significant storm drain improvements to address drainage system capacity deficiencies.  The project area is susceptible to localized flash flooding due to the large contributing watershed of the Pah Rah range, located immediately to the east.  As recently as 2015 and 2017, the East Prater Way and Vista Boulevard intersection was closed to traffic for several hours due to flood water inundation which extended north along Vista Boulevard and west along Prater Way.  Attachment “02 – Project Vicinity Flood Photos” contains photographs of the typical flooding experienced near the intersection.

The objective of the project is to improve stormwater conveyance to mitigate flood impacts to the traveling public and surrounding residential / commercial properties for the 5-year storm recurrence interval.  Project evaluation and engineering design were approved in the FY18 CIP.  Budget for project construction was originally approved for the FY19 CIP.  During the project evaluation analysis, it was determined that upsizing the existing gravity storm drain infrastructure would not adequately convey the stormwater to mitigate impacts for the 5-year design storm event.  Stormwater that arrives at the East Prater Way and Vista Boulevard intersection must be conveyed to the North Truckee Drain so that it can ultimately be conveyed to the Truckee River. 

The most direct routing from the intersection to the North Truckee Drain is along East Prater Way, which contains significant existing storm drain infrastructure including a 60-inch gravity main on the south side of the roadway and a 42-inch gravity main on the north side of the roadway.  The hydraulic modeling concluded that adding more gravity drainage infrastructure or upsizing the existing infrastructure would not mitigate flood impacts for the 5-year design storm.  This led the design team to investigate an alternative that consisted of a storm drain pump station and force main, which is capable of conveying significantly more stormwater, to the North Truckee Drain, through a smaller diameter pipe, compared to a gravity main.  While the alternative design mitigated the impacts of the 5-year storm, it increased the project cost estimate due, primarily, to the capital costs associated with constructing a pump station.  The City currently operates storm water pump stations at the corner of Glendale Ave and Meredith Way, and at Snider Way and Steneri Way. 

The design team performed a cost benefit analysis to determine how the benefit from the pump station alternative compared to the additional cost.  Attachment “04 – Benefit Cost Analysis Memo” summarizes the analysis performed.  The team first identified the costs associated with the project which include the initial capital construction cost, annual operations and maintenance, and pump / equipment replacement.  The project is designed for a 60-year life cycle with planned pump replacement at 30 years. 

Next, the design team worked with City staff to identify and quantify the benefits of the project.  Historically, storms that replicate the 5-year design storm have caused the intersection to be closed for nearly 12 hours to allow for flood waters to recede and debris cleanup.  Specifically, five areas of impact were identified and analyzed for the 12-hour closure:  direct costs to close the intersection, the impact to the traveling public, the impact to emergency response services, impact to businesses, and environmental impacts.  The intersection accommodates approximately 28% of the north/south travel through Sparks which equated to an average annual daily traffic count of 27,100 vehicles.  The intersection provides primary access to Northern Nevada Medical Center, Arbors Memory Care, and Renown Urgent Care-Vista.  Additionally, DaVita Sparks Dialysis Center and Brookdale Vista / Sparks Senior Living Facilities are located adjacent to the intersection.  The Sparks Police Department is located 1,700 feet west of the intersection, flood waters from the 2015 and 2017 events inundated E Prater Way west of the Police Department which restricted access to Sparks Boulevard and Vista Boulevard to police vehicles.

The financial impact associated with closure of the intersection and flood water inundation along E Prater Way and Vista Boulevard was calculated to be $1,396,000 for the 5-year design storm, based on the five areas of impact analyzed.  Comparing the financial impact of the design storm recurring over the life cycle of the project, it was determined that the benefit to cost ratio of the project would exceed 1.0 after 15 years of service.  That is, after 15 years the benefit would be greater than the cost of the project.  Over the remainder of the project life cycle the benefit continues to increase ultimately reaching a ratio of 3.0 at the end of the lifecycle.     

Based on the benefit cost ratio, staff directed the design team to proceed to final design with the pump station alternative.  The additional budget associated with the pump station alternative was approved with the FY21 CIP.   

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.