California Construction General Permit Web Conference. Session III: Hydromodification Management

Transcription

1 California Construction General Permit Web Conference Session III: Hydromodification Management Wednesday, November 18, :00 p.m. 1:30 p.m. For audio participation Dial: ; Passcode Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but Presenters Wayne S. Rosenbaum Partner Foley & Lardner LLP Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 1

2 Presenters Dennis C. Bowling, PE, MS Principal Rick Engineering Company Presenters Jayne Janda-Timba, PE Associate Rick Engineering Company Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 2

3 Presenters Shaun Flater, CPSWQ, CPESC Division Manager Whitson CM Inc. Presenters David Roberts, PhD Environmental Scientist Nautilus Environmental Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 3

4 Housekeeping Materials are available on our Web site at or simply click the print icon on the bottom right hand side of your screen to print to a PDF. Call for technology assistance Dial *0 (star/zero) for audio assistance Ample time for live Q & A will be allotted at the end of the formal presentation We encourage you to Maximize the PowerPoint to Full Screen Usage: - Hit F5 on your keyboard; or - Select View from the toolbar menu and click Full Screen Outline What is hydromodification? Strategies for hydromodification management What requirements apply to you? Comparison of Construction General Permit, San Diego County MS4 Permit, and Ventura County MS4 Permit: approaches and challenges Planning for hydromodification standards Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 4

5 What is Hydromodification? Q Q Q The alteration of the hydrologic characteristics of coastal and noncoastal waters, which in turn could cause degradation of water resources. Hydromodification can cause excessive erosion and/or sedimentation rates, causing excessive turbidity, channel aggradation and/or degradation (Construction General Permit). The change in the natural watershed hydrologic processes and runoff characteristics (i.e., interception, infiltration, overland flow, interflow and groundwater flow) caused by urbanization or other land use changes that result in increased stream flows and sediment transport (condensed from San Diego County MS4 Permit). The alteration away from a natural state of stream flows or the beds or banks of rivers, streams, or creeks, including ephemeral washes, which results in hydrogeomorphic changes (Ventura County MS4 Permit). What is Hydromodification? Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 5

6 Pre-Development Hydrology Source: LOW IMPACT DEVELOPMENT Technical Guidance Manual for Puget Sound. Puget Sound Action Team, Washington State University Pierce County Extension. January Graphic by AHBL Engineering. Post-Development Hydrology Source: LOW IMPACT DEVELOPMENT Technical Guidance Manual for Puget Sound. Puget Sound Action Team, Washington State University Pierce County Extension. January Graphic by AHBL Engineering. Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 6

7 Causes of Hydromodification Effects of land development on the site runoff flow pattern Less infiltration/evapotranspiration Runoff conveyed in impervious system (e.g., storm drain) directly to creek (increased connectivity) More surface runoff (increased volume) Faster surface runoff (increased peak flows) Runoff occurs more often (increased duration) Higher flows that last for longer durations provide the energy necessary to increase the amount of erosion in local creeks Hydromodification Impact to Sediment Balance Degradation = Scour Aggradation = Deposition Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 7

8 Hydromodification Impact to Sediment Balance Hydromodification Impact to Sediment Balance Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 8

9 Hydromodification Impacts Hydromodification begins at the discharge point from engineered systems. The sediment ends up somewhere else. Storm drain outfall Inlet of a roadway culvert What is Hydromodification? How is the flow change quantified? Increase in duration of runoff Increase in frequency of runoff What causes these increases in duration and frequency? Increased imperviousness (increased runoff coefficient, increased runoff volume) Increased efficiency of conveyance (reduced time of concentration) Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 9

10 Quantification of Flow Changes Increased duration means a creek will experience a given flow rate for more time. For example, over a 35 year period, a flow rate of 0.1 cfs may occur for 1,166 hours in the postproject condition vs. only 429 hours in the pre-project condition. Figure 1 (next slide) shows a flow duration curve for a hypothetical development. The three curves show what percentage of the time a range of flow rates are exceeded for three different conditions: pre-project, post-project, and postproject with storm water mitigation Figure 1: Flow Duration Curve Post-Project Flow (cfs) Pre-Project Flow (cfs) Post-Project Mitigated Flow (cfs) Pre-Project 0.2Q5 Pre-Project Q Flow (cfs) % Time Exceeded Notes: % Time exceeded refers to the percent of the total model simulation period (e.g., 35 years). This example is for San Diego, where the Interim Hydromodification Management Criteria range of flow rates to control is 0.2Q5 to Q10 based on continuous simulation modeling. Source: San Diego County Hydrograph Modification Plan Using Continuous Simulation to Size Storm Water Control Facilities, Brown and Caldwell, May 9, 2008, Available at Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 10

11 Quantification of Flow Changes Increased frequency means a creek will experience a given flow rate more frequently. For example, a flow rate of 0.5 cfs might occur on a 1.5-year return period in the post-project condition vs. a 5-year return period in the pre-project condition, or in other words, more than 3 times as often. Figure 2 (next slide) shows a peak flow frequency curve for pre-project, post-project, and post-project with storm water mitigation scenarios. The curves indicate how often a particular flow rate would be equaled or exceeded. Figure 2: Peak Flow Frequency Curve Post-Project Peak Flow (cfs) Pre-Project Peak Flow (cfs) Post-Project Mitigated Flow (cfs) Pre-Project 0.2Q5 0.7 Peak Flow (cfs per acre) Recurrence Interval (years) This example is for San Diego, where the Interim Hydromodification Management Criteria range of flow rates to control is 0.2Q5 to Q10 based on continuous simulation modeling. Source: San Diego County Hydrograph Modification Plan Using Continuous Simulation to Size Storm Water Control Facilities, Brown and Caldwell, May 9, 2008, Available at Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 11

12 Hydromodification Control What can we do to control hydromodification? Preserve streams and use natural conveyance systems Find a way to not discharge the excess runoff volume from new impervious areas (volume-matching approach): Infiltrate the excess runoff volume, or Store the excess runoff volume on-site for evaporation or re-use Hydromodification Control When it is not feasible to infiltrate / evaporate / reuse excess runoff on-site, discharge the excess volume at a flow rate that is less than the critical channel flow rate that would cause erosion of the receiving channel (force-matching approach).* *The option to discharge excess volume is not available in all Permits Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 12

13 Hydromodification Control Q LID approach Volume-matching approach Generally available in all Permits Use natural conveyance systems Disconnect impervious areas Use smallscale engineered devices in urban areas Hydromodification Control Q Flow control approach Force-matching approach Not available in all Permits Detention Basin Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 13

14 What Requirements Apply to You? Hydromodification management requirements vary depending on jurisdiction. Is the project within a: Phase I Municipality? Phase II? Designated Municipality? Non-Designated Municipality? Non-Traditional MS4? Use the flow chart on the next slide to determine applicable requirements Which Permit Applies To Me? No Is the project located in a Is the project located in a Phase II MS4 Phase II MS4 No Is the project located in a Is the project located in a Phase 1 MS4 Phase 1 MS4 Yes Yes No Does the SWMP include Does the SWMP include post construction hydromodification BMPS post construction hydromodification BMPS No Does the JURMP include Does the JURMP include post construction hydromodification BMPS post construction hydromodification BMPS Yes Yes Follow the hydro-modification BMPS in Follow the hydro-modification BMPS in the SWMP the SWMP Follow the hydro-modification BMPS in Follow the hydro-modification BMPS in JURMP JURMP Follow the post construction Follow the post construction procedures in the General Construction procedures in the General Construction Storm Water Permit Storm Water Permit Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 14

15 Types of Permits Water Balance Construction General Permit Energy Balance San Diego County MS4 Permit Water Retention Ventura County MS4 Permit Water Balance Construction General Permit Replicate pre-project water balance Limited use of structural controls Preserve pre-construction drainage density and time of concentration Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 15

16 Pre-Project Project Water Balance Replicate the pre-project water balance The volume of rainfall that ends up as runoff for the smallest storms up to the 85 th percentile storm event. Volume that can not be addressed using nonstructural practices shall be captured in structural BMPs approved by the regional board. Inform the Regional Water Board staff at least 30 days prior to the use of any structural control measure used to comply with this requirement. Document the infeasibility of using non-structural practices, OR Document that there will be fewer water quality impacts. Structural Controls Allowable controls without permission of Regional Board: Porous Pavement Tree Planting Downspout Disconnection Impervious Area Disconnection Green Roof Stream Buffer Vegetated Swales Rain Barrels and Cisterns Landscaping Soil Quality Discharger shall demonstrate compliance by submitting a map and worksheets with NOI in accordance with Appendix 2. Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 16

17 Drainage Density and Time of Concentration Discharge shall preserve the pre-construction drainage density. Miles of stream length per square mile of drainage area Includes first order streams or larger. First order streams are streams with no tributaries Post-construction time of runoff concentration is equal or greater than pre-construction time of concentration. Energy Balance The San Diego County MS4 Permit Manage increases in runoff discharge rates and durations where such increased rates and durations are likely to cause: Increased erosion of channel beds and banks, Sediment pollutant generation, or Other impacts to beneficial uses and stream habitat due to increased erosive force. Post construction runoff discharge rates and durations shall not exceed estimated pre construction discharge rates and durations. Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 17

18 Water Retention The Ventura County MS4 Permit Reduce runoff volume emanating from impervious surfaces through infiltration, storage for reuse, evapotranspiration, or bioretention/biofiltration by reducing the percentage of Effective Impervious' Area (EIA) to 5 percent or less of the total project area. Permit Selection Opportunities for Phase II Without a SWMP Construction Storm Water Permit JPA with an adjoining Phase I Develop a SWMP Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 18

19 Planning for Hydromodification Standards Hydromodification management is not an end-of-pipe storm water management strategy End-of-pipe strategy is not consistent with intent of LID, and is not an option in some Permits. Hydromodification flow-control basins, when allowed, are often much larger than traditional detention basins. Flow-control basin outlet structures are extremely small and susceptible to clogging. Drawdown times may conflict with local vector control requirements. Structural controls are more maintenance intensive than non-structural practices. Planning for Hydromodification Standards Hydromodification controls can not be retrofit into a project at the end of the design process Hydromodification controls are dispersed throughout projects. They are generally non-structural practices (runoff dispersion, impervious area disconnection). Structural practices for hydromodification control are not structures that drop neatly inside storm drain systems. Flow-control basins use up valuable land. Properly designed dispersed controls can enhance the property when incorporated from the start of the design process and when all necessary parties are involved in the design. Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 19

20 Planning for Hydromodification Standards Many parties need to be involved in the planning and design of hydromodification controls / LID practices: Owner Planner Architect Civil Engineer Landscape Architect Geotechnical Engineer Planning for Hydromodification Standards Planning starts from the purchase of the property What are your hydromodification requirements (Construction General Permit or local Storm Water Management Plan)? Can excess runoff from new impervious areas be infiltrated on the property? Could excess runoff be stored for evaporation or re-use? What is the pre-project stream density? Can it be preserved? Are there any possible exemptions, such as credits for redevelopment of existing impervious areas? Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 20

21 Planning for Hydromodification Standards Don t count on exemptions Some Permits do not have any exemptions from hydromodification management requirements. Even if the site discharges to a non-erodible system, volumematching may be required because excess runoff can increase the pollutant load discharged from the site. Alternative compliance measures involving off-site properties or collaboration with additional parties may be more arduous than hydromodification management requirements. References: Construction General Permit State Water Resources Control Board National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges Associated with Construction and Land Disturbance Activities, Order No DWQ, NPDES No. CAS000002, September 2, 2009 San Diego County Municipal Separate Storm Sewer System (MS4) Permit California Regional Water Quality Control Board San Diego Region Order No. R NPDES No. CAS Waste Discharge Requirements for Discharges of Urban Runoff from the Municipal Separate Storm Sewer Systems (MS4s) Draining the Watersheds of the County of San Diego, the Incorporated Cities of San Diego County, the San Diego Unified Port District, and the San Diego County Regional Airport Authority, January 24, 2007 Ventura County Municipal Separate Storm Sewer System (MS4) Permit California Regional Water Quality Control Board Los Angeles Region, Order NPDES Permit No. CAS Waste Discharge Requirements for Storm Water (Wet Weather) and Non-Storm Water (Dry Weather) Discharges from The Municipal Separate Storm Sewer Systems within the Ventura County Watershed Protection District, County of Ventura and the Incorporated Cities Therein, May 7, 2009, re-transmitted June 2, 2009, and errata dated June 3, 2009 Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 21

22 Contact Us S. Wayne Rosenbaum, Esq. Foley & Lardner LLP Dennis C. Bowling, M.S., P.E. Rick Engineering Company Shaun Flater, CPSWQ, CPESC Whitson CM Inc David Roberts, PhD Nautilus Environmental (x226) Jayne Janda-Timba, P.E. Rick Engineering Company Thank You! A copy of the PowerPoint presentation and a multimedia recording will be available on our website early next week. Continue the discussion! Ask a question or post a comment about the new Construction General Permit on the Whitson CM blog: Attorney Advertising Prior results do not guarantee a similar outcome Models used are not clients but 22