City of Stockton Municipal Utilities Department
Stormwater Master Plan
Final Report
| Executive Summary 1
Executive Summary
The City of Stockton Stormwater Master Plan (SWMP) was developed with the primary purpose of identifying the extent and nature of flooding under existing and future conditions and developing Capital Improvement Plan (CIP) projects that could be implemented to alleviate this flooding. The City is situated on the eastern boundary of the Sacramento-San Joaquin River Delta, with stormwater drainage provided by open (channels) and closed (pipes) conveyance infrastructure. Portions of the City are protected by levees, with pump stations serving a key role in stormwater conveyance throughout the City to discharge runoff collected behind these levees and support drainage relief in low-lying areas.
PCSWMM (PC-Stormwater Management Model) was utilized to model the hydrology and hydraulics of the City’s stormwater infrastructure. The modeling efforts focused on the 10-yr, 24-hr design storm event, consistent with existing City standards. Management of flooding for larger events, such as the 200-yr flood, are typically provided by improvements to levees, larger channels and infrastructure managed by Municipal Utility Department’s (MUD) partner agencies. The focus of this stormwater master plan is urban stormwater conveyance infrastructure like inlets, pipes, and pump stations which are rarely themselves sized for the 200-yr event but could be affected by levee and channel improvements. Long- term coordination is expected to be beneficial in ensuring stormwater improvements outlined within this master plan are compatible with levees and other flood infrastructure improvements developed by others.
Modeling efforts presented herein examined existing conditions in addition to future anticipated development identified by City staff and the 2040 General Plan. The location and extent of areas of study for H&H modeling were established and prioritized in coordination with City staff to evaluate areas of known flooding concerns and areas of anticipated future development. H&H model results were used to identify concern areas based upon modeled surface inundation.
A limited elevation survey effort was undertaken to assess the accuracy of existing stormwater inventory data. This effort supported the use of LiDAR to establish structure rim elevations; however, pipe depths and geometries were sometimes missing or inconsistent. Standard assumptions were applied to stormwater infrastructure data to address apparent gaps and inconsistencies. Additional data during future details design phase efforts should be collected to evaluate the suitability of these assumptions and refine model results accordingly.
Improvement concepts to address flooding in concern areas were developed utilizing the PCSWMM model to determine infrastructure improvements that would alleviate modelled flooding. Potential stormwater improvements generally involved multiple typologies, including:
• Upsizing gravity conveyance infrastructure
• Pump station improvements
• Detention facilities
A total of 12 improvement concepts were developed, with costs ranging from under $5 million to over $75 million. These improvement concepts were grouped into high, medium, and low priority categories based upon stakeholder coordination efforts. Substantial costs of these identified improvements can be attributed to the nature of flooding concerns, depth of existing infrastructure, and need for pump station improvements. In addition to these larger CIP projects, opportunities exist to address smaller-scale DRAFT
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ATTACHMENT D
City of Stockton Municipal Utilities Department
Stormwater Master Plan
Final Report
| Executive Summary 1
drainage deficiencies and maintenance needs throughout the City, such as pump station rehabilitation and localized pipe and inlet replacement.
Project Cost Priority
Boggs Tract $17,144,585 High
Bonnie Brook $11,547,232 High
Hwy 4 and San Joaquin $24,902,729 High
Walker Turnpike Alt 1 * $46,204,468 High
Walker Turnpike Alt 2 + Eighth St and San Joaquin * $75,142,267 High Bianchi and Calaveras $30,682,180 Medium
Duck Creek $12,061,203 Medium
Legion Park and Smith Canal $50,864,178 Medium
Deep Water $10,229,853 Low
Little Johns $4,552,126 Low
Mormon Slough $27,524,026 Low
Sutter and Calaveras River $13,710,877 Low
West Lane and Calaveras River $6,517,147 Low
* Denoted projects are alternatives and would not both be implemented An assessment of the Stormwater Utility Division’s baseline financials indicates that expenditures are projected to increase at a higher rate than revenues, which only considers operational costs and excludes capital investments to improve stormwater infrastructure. Multiple funding mechanisms available to the City were evaluated and would be necessary to support ongoing operations and any future capital investments. Implementation of a reliable and predictable stream of revenues sufficient to cover Stockton’s long-term operation expenditures and the capital costs of the SWMP’s high and medium priority projects is recommended.
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ATTACHMENT D