hydromodification compliance in the bay area
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Hydromodification Compliance in the Bay Area. Presented by Norman Gonsalves Caltrans District 4 July 2010. What is HYDROMODIFICATION?. The alteration of natural stream hydrology by human activity. Why could HM be a problem?. Stream bank and stream bed erosion Sedimentation - PowerPoint PPT PresentationTRANSCRIPT
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Hydromodification Compliancein the
Bay Area
Presented byNorman Gonsalves
Caltrans District 4
July 2010
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What is HYDROMODIFICATION?The alteration of natural stream hydrology by human activity.
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Why could HM be a problem?
Stream bank and stream bed erosion Sedimentation Increased pollutant delivery to receiving waters Decreased salinity in estuaries and coastal
areas
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Stream bank erosion
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Stream bed erosion
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Sedimentation
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Flooding (sedimentation)
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What causes HM?
Increased runoff volume from upland areas Channel lining and armoring Channel entrainment and straightening Flow impounding
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Increased runoff volume
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Channel lining
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Channel armoring
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Channel entrainment (levee)
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Who considers HM a problem?
The USEPA, but leaves regulation to states. States include Washington, California, others. California counties regulating HM include: Alameda (west) Contra Costa (all) Santa Clara (west) San Mateo (all) San Diego (all) Los Angeles (all)
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What are the requirements?
For areas with HM regulations: Do not exceed pre-project flow peak flows Do no exceed pre-project flow durations, from
0.1*Q2 to Q10 Applies to projects discharging to susceptible
receiving waters Applies to projects with 1 acre or more of added
impervious surfaces Applies to Caltrans projects requiring 401
Certification
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Flow-duration curves
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Susceptible receiving waters
Water bodies that are NOT susceptible include:• Bays, oceans, large lakes and reservoirs;• Tidal reaches;• Channels lined, armored or piped for their
entire lengths all the way to (1) or (2) above;• Aggrading channels
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Exempted projects Projects with less than 1 acre of added
impervious area Projects discharging to non-susceptible water
bodies Infill projects (> 65% impervious area) in highly
developed watersheds (< 10% vacant parcels)
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Example of exempt areas
Susceptibility map.
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Basic ways to meet HM requirement Infiltrate excess volume created by added
impervious areas Discharge excess volume below erosive flow
rates of receiving waters (0.1Q2 pre-project), using storage structures
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Storage structures for HM management
Storage structures, including: Basins (lined or unlined), Underground storage pipes, Ditches (lined or unlined), Sand filters, Bio-retention systems
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Infiltration devices for HM management
Infiltration basins, Infiltration trenches, Bio-retention systems, Unlined detention basins, Unlined ditches, Biostrips, Embankment side slopes, Other pervious surfaces
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Design tools for HM management Bay Area Hydrology Model (BAHM) (proprietary,
but free version available) Hydrological Simulation Program – Fortran
(HSPF) (EPA, free) Storm Water Management Model (SWMM)
(EPA, free)
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Tools compared
HSPF – powerful but hard to use. No built-in data.BAHM – based on HSPF, user-friendly, set up
specifically for HM, built-in data for 4 Bay Area counties, but unstable and buggy.
SWMM – can calculate HM devices as part of entire drainage system, fairly user-friendly, no built-in data, less capable infiltration model.
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BAHM – Select Project Site
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BAHM – Add A Watershed
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BAHM – Add A Detention Pond
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BAHM – Review Results
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BAHM – Produce Report
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BAHM – Pond Elements
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BAHM Tank and Channel Elements
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BAHM – More Devices
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BAHM – Outlet Structures
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SWMM – User interface
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SWMM – LID + Drainage Calcs
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SWMM – Drainage Profile