HomeMy WebLinkAboutIII. A. STORMWATER MASTER PLAN UPDATESTORMWATER MASTER PLANS
C.J. Bodnar, PE
September 10, 2024
Background
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Last Approved Stormwater Master Plan
Last Approved Stormwater Master Plan completed in the 1990s
Stormwater Master Plan – Why Update
•Update Stormwater system inventory
•Create computer models of the existing
stormwater system
•Assess the performance of the stormwater system
−Flood control
−Stormwater quality
•Identify deficiencies in the stormwater
system
•Determine needed improvements
•Provide information for project designs 4
Stormwater Master Planning, Analysis,
and Inventory, CIP 100406
•In 2014 this project was added to the
Capital Improvement Program (CIP)
•The total investment to evaluate current
and future flood impacts and develop
long-term flooding solutions is $19.6 M.
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Process for Master Plan Update
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Data Collection
•Continuous Process
-Verify existing information
-New pipes and structures
•City survey crews collecting data every day
since October 2015
•Survey Division surveyed over 32,000
structures to date
•Incorporated Stormwater Structure information
from Norfolk, Chesapeake, JEB Little Creek and
NAS Oceana
•Incorporated As-Builts provided by DSC
and PW Operations
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Model Construction
•Modeling all drainage basins
•All models prepared in PCSWMM
Except for Lower Southern Rivers
•PCSWWM uses EPA SWMM as its engine
•Lower Southern Rivers models prepared in MIKE suite of programs
•Allows effects of wind into the modeling
parameters
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Model Construction
•Models include the Primary Stormwater System:
-Stormwater pipes larger than 24 inches in diameter
-Stormwater management facilities (ponds and lakes)
-Natural conveyance systems (ditches/swales/canals)
•Models prepared for 1-, 2-, 10-, 25-, 50-, 100- and 500-year storm events
under PWDSM requirements using recurrent tailwater elevations
•Models prepared for 1.5-ft and 3-ft sea level rise
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Comparison of 1990 Master Plan to Now
1990 Model Schematic:
46 nodes, 58 conduits
2024 Model Schematic:
35,680 nodes, 52,836 conduits
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Model Validation
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Model Validation
•With rainfall data and downstream boundary
conditions, models can be
run to simulate a storm event
•On average, City models
are validating to roughly
½ an inch
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2.0 Drainage Basin Models
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•Adding 15-inch diameter pipes
•Using the latest available DEM
Old Linkhorn Bay
•145 Subcatchments
•227 Junction Nodes
•111 Storage Nodes
•387 Conduits
2.0 Linkhorn Bay
•852 Subcatchments
•546 Junction Nodes
•712 Storage Nodes
•1884 Conduits
Stormwater Master Plan
Development
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Master Plan
Development
•Models provide locations where flooding is
anticipated
-2-, 10-, 25-, 50- and 100-year storms
classified as simulated flooding area
•The Master plan evaluates each simulated flooding area
-Develops various alternatives to resolve flooding
-Ranks those Alternatives to develop a proposed project
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Criteria Flow Chart
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Master Plan Criteria
Criteria Establishment:
•Analytic approach to prioritize projects for implementation
•Criteria developed across multiple City departments:
-Public Works: Stormwater, Operations, Transportation, Stormwater Regulatory
-Public Utilities
-Planning
-City Manager’s Office
-Economic Development
-Agriculture
-Housing
-Emergency Management
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Alternative Selection Criteria
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Project Selection Criteria
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Stormwater Master Plans
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CIP Project Detail Sheet
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Conceptual
Plan of
Improvements
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Flood Improvement Map
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Opinion of Probable Construction Costs
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Stormwater Master Plan Summary
•Stormwater Master Plans are a vision for the future similar to the City’s Master Transportation Plan or Comprehensive Plan.
•Stormwater Master Plans evaluate our current situation and outline the necessary actions to ensure the resilience of our City by identifying practical and equitable strategies.
•Stormwater Master Plan 9-year effort developed the following:
•Stormwater models that identify where flooding is expected to occur and can be used for designing Capital Improvement Program (CIP) projects and private projects
•Stormwater conceptual plans to mitigate flooding to meet the Public Works Design Standards Manual
•Objective prioritization criteria
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THANK YOU.
Questions?
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