Minimizing Flood Risks and Habitat Impacts Due to Post-Flood Recovery Efforts

Transcription

1 Minimizing Flood Risks and Habitat Impacts Due to Post-Flood Recovery Efforts Roy Schiff, Milone & MacBroom, Inc. Mike Kline, Vermont Agency of Natural Resources Shayne Jaquith, Vermont Agency of Natural Resources Barry Cahoon, Vermont Agency of Natural Resources Jim MacBroom, Milone & MacBroom, Inc. Evan Fitzgerald, Fitzgerald Environmental Associates, LLC Source: Lars Gange & Mansfield Heliflight, August 31, 2011

2 Source: Lars Gange & Mansfield Heliflight, August 31, 2011

3 Roaring Branch Bennington, VT 9/1/2011

4 Source: VDFW, 2011

5 Source: VTDEC, 2012

6 77 miles of dredging after Irene (VTDFW) 176 miles of historic straightening in the same watersheds (VTDEC) Less Vulnerability 20% 0% Same Vulnerability 40% 40% More Vulnerability 40% 60% Source: VTDFW, 2011

7 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 1. Perform an alternatives analysis based on risk minimization, limiting habitat impacts, and controlling project cost. Consider the no-action alternative first.

8 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 2. Link flood PRIMARY DAMAGE OBSERVATIONS damages to river processes for proper problem identification. DAMAGE DETAILS RIVER CHANNEL CONDITIONS RIVER PROCESSES

9 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 3. Consider scale. Prepared by VTDEC

10 Source: Collins, 2009

11 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 4. Follow the principles of fluvial geomorphology and current best engineering practice. Source: Landslide Natural Resources Planning, 2013

12 Source: Schumm and Watson, 1984; Simon 1989; FISRWG, 1998

13 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 5. Restore reference geometry. Evaluate stream power v. resistance to erosion. Q 100 Q 10 Q Bankfull Low- Flow Channel Bankfull Channel River Corridor 100-Year Floodplain

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15 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 6. Restore floodplain connection to limit future in-channel work. Historic Fill Restored Floodplain

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17 Total Power decreases range W/m2 (948 to 167) Flood velocity decreases 1-4 feet per second Flood depth decreases feet

18 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 7. Manage channels towards a least erosive, vertically stable equilibrium. SEDIMENT WATER Source: Lane, 1955; Rosgen and Silvey, 1996

19 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 8. Dredge only where infrastructure and buildings are vulnerable to damage.

20 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 9. Properly size bridges and culverts VT Stream Alteration General Permit (GP) Design Requirements W structure = 1.0 x W bankfull channel so that they are geomorphically compatible and H opening = 4 x D bankfull channel D embed = 30% H opening or D 84 for boulder bed, whichever larger Match channel profile and create uniform longitudinal transitions at inlet and outlet. Structure shall not obstruct aquatic organism passage. maintain AOP.

21 VERMONT STANDARD RIVER MANAGEMENT PRINCIPLES AND PRACTICES: Guidance for Managing Vermont s Rivers Based on Channel and Floodplain Function 10. Conserve river corridors to provide space for the river to reduce flood risks and the need for flood recovery.