Impact of Storm Drains on Urbanized Alluvial Fan Flooding in Ventura County, California Presented to: FMA Annual 2015 Conference September 8-11, 2015 Presented by: Jim O Brien, Ph.D., P.E. Noemi Gonzalez, Ph.D.
We ve come a long way with urban detail. From 1-D single discharge flood assessments to Typical HEC-RAS Cross Section for a Single WSE
Eventually the flood mapping community will graduate from this to this
2-D flood hydrograph routing Larger projects, smaller grid elements, detailed and integrated models Show animation Hohokam
FLO-2D Model Components 2-D overland unconfined flow in 8-directions Channels: rectangular, trapezoidal or cross sections Computes channel-floodplain exchange flow Rainfall, infiltration and evaporation Buildings Streets Dam and levee breach Simulates sediment transport and mud/debris flows Hydraulic structures: bridges, culvert, weirs Storm drains Groundwater
FLO-2D Primary Features Physical process model Conserves volume and reports on it Combined hydrologic and hydraulic model Unconfined flooding with no boundary conditions or hot starts Routes entire hydrograph Variable timesteps enable fast simulations
FLO-2D Storm Drain Component Fully integrated surface and storm drain model: FLO-2D complete surface water hydrology and hydraulics model. Storm drain component solves the pipe hydraulics for each surface water model computational timestep.
FLO-2D Pro Storm Drain Pipe System Rainfall, inflow hydrographs Surface Hydrology/Hydraulics Outlet nodes, infiltration, evaporation Dynamic Link Bidirectional flow exchange - user assigned features Inflow from upstream systems (external hydrology) Closed Conduit Network - Pipe Hydraulics Oufalls, outlets, junctions, overflow, etc.
FLO-2D Storm Drain Increased Accuracy and Detail over other SWMM Based Models Worked with the FCDMC in Arizona: Storm drain inlet discharge ~ f(head, inlet geometry) Return flow is based on Head not Rim elevation Volume conservation Surface water - storm water exchange timestep Outfall enhancements Street cross slope Stability and automated data input
FLO-2D Storm Drain Inlet Control
FLO-2D Storm Drain Manhole Simulation Manhole covers can pop and stay off with return flow to surface water.
Outfall Advantage o Pipe discharge can be removed from the SD system or returned to the SW as a user defined option. o This outfall flexibility represents an enhancement.
Ventura County, California Example Project Urban Storm Water Analysis Total Project ~ 10 sq. mi.
Lots of Details Spatially variable floodplain roughness Buildings Streets Channels Hydraulic structures Storm drain system Completed in 6 month
Database Mainly using GIS data: Parcels Streets Right-of-Way Land Use Storm drain system atlas: main lines, laterals, catch basins/inlets, open channels, box conduits, etc. Roofline polygons (building footprints)*
Floodplain Roughness
Hydrology Options Off site return period flood inflows Rainfall frequency events NEXRAD replicate storms Integrate with Santa Clara River flows Infiltration Groundwater Spatially and temporally variable rainfall
Channel System
Storm Drain System
Storm Drain Model - Details Channel flows enter a closed conduit for about 5000 ft through the urban environment. The storm drain system redistribute flood volumes through the urban environment
Storm Drain Network 9 independent storm drain lines with 250 conduits, 174 inlets, 9 outfalls Pipes ranged from 1ft to 9ft in diameter Pipe lengths ranges from 20 to 800 ft with a total of 6.6 miles of pipes The pipe capacity ranged from 2 cfs to 3,500 cfs
Hydraulic Structures - 90
Flood Damage $$ for Depths > 0.5 ft
10yr Flood Animation Risk Analysis
Without Storm Drain 10-year flood
With Storm drain 10-year flood Impact
Questions?