Urban Levee Design Criteria and Central Valley Flood Protection Plan Levee Vegetation Management Strategy

Transcription

1 Urban Levee Design Criteria and Central Valley Flood Protection Plan Levee Vegetation Management Strategy Presented at California Levee Vegetation Research Symposium August 30, 2012 by Rod Mayer 1

2 Overview The Hard Question 2009 Framework Agreement Urban Levee Design Criteria & CVFPP Levee Vegetation Management Strategy Criteria and Strategy Achievements Criteria and Strategy Refinements 2

3 The Hard Question What should we do about existing trees on levees? Many considerations, including: - Flood risk - Environmental - Financial - Practicality Considering only flood risk: - Some trees okay - Some trees not okay - How do we sort it out? 3

4 USACE ETL Figures 4

5 USACE ETL Figures 5

6 USACE ETL Figures 6

7 USACE ETL Figures 7

8 2009 Framework Agreement 8

9 2009 Framework Agreement 9

10 2009 Framework Agreement Accomplishments Established trimming and thinning inspection and access criteria Prevented new trees from establishing, except on lower waterside levee slope Continued PL eligibility until 2012 CVFPP adoption Provided time to improve vegetation policies Provided forum for working together 10

11 2009 Framework Agreement Shortcomings Inspection and access-based criteria suitable for the temporary nature of the Framework Agreement Some things left undefined or unclear Left unaddressed: - How USACE would handle Section 408 approvals involving legacy levee vegetation - How USACE would formulate federal projects involving legacy levee vegetation 11

12 Urban Levee Design Criteria (ULDC) and CVFPP 12

13 Urban Levee Design Criteria Criteria and Guidance for Design and Evaluation Design Water Surface Elevation Minimum Top of Levee Soil Sampling, Testing, and Logging Slope Stability for Intermittently Loaded Levees Underseepage for Intermittently Loaded Levees Frequently Loaded Levees Seismic Vulnerability Levee Geometry Interfaces and Transitions Erosion Right-of-Way Encroachments (Excluding Penetrations, Closure Structures, and Levee Vegetation) Penetrations Floodwalls, Retaining Walls, and Closure Structures Animal Burrows Levee Vegetation Wind Setup and Wave Runup Security Sea Level Rise Emergency Actions Criteria and Guidance for Operation and Maintenance 13

14 2009 Framework Agreement Areas to Improve Define immature trees Clarify root removal requirements Provide for evaluations of trees that may pose a threat to levee integrity Require removal/remediation of trees posing a threat to levee integrity Define Life Cycle Management and area subject to it Clarify short levees Identify planting and natural reestablishment areas 14

15 ULDC & CVFPP Levee Vegetation Management Strategy Life Cycle Management in the Vegetation Management Zone - Remove immature trees (less than 4 inches DBH) - May retain mature trees - Trim up and thin retained trees Evaluate all trees and remove/remediate if pose an unacceptable threat to levee integrity Remove roots within 3 feet of stump, or beyond May retain and allow new trees on lower waterside levee slope without trimming or thinning Planting/revegetation allowed on waterside slope planting berm and natural ground 20 waterward of levee crown 15

16 ULDC & CVFPP Levee Vegetation Management Strategy 16

17 ULDC & CVFPP Levee Vegetation Management Strategy 17

18 ULDC & CVFPP Levee Vegetation Management Strategy 18

19 ULDC & CVFPP Levee Vegetation Management Strategy 19

20 Criteria and Strategy Accomplishments Pragmatic, Interim Criteria and Strategy - Time-out while we assess the situation - Flexible and adaptive to experience and increased knowledge - Avoid increasing potential flood risk posed by new vegetation in VMZ - Avoid near-term widespread significant environmental impacts - Time to develop conservation strategy for mitigating impacts and improving the environment 20

21 Criteria and Strategy Accomplishments Provides path toward long-term compatibility Through long-term implementation of life-cycle vegetation management on the landside slope, crown, and upper waterside slope of SPFC levees, the CVFPP levee vegetation management strategy will gradually (over a period of decades) result in levees clear of woody vegetation, consistent with USACE vegetation policy, except for lower waterside vegetation which is mostly the same part of the levee where USACE has indicated that variances can be appropriate. - Quote from CVFPP 21

22 Criteria and Strategy Refinements Engineers and levee maintaining agencies could use additional guidance Much more work is needed - Scientific research - Literature research - Sharing and documentation of experiences and best management practices 22

23 Criteria and Strategy Refinements Which trees pose an unacceptable threat to levee integrity? - Species - Health of tree - Location of tree - Loading conditions - Levee properties When should dead trees be removed? 23

24 Criteria and Strategy Refinements When should root removal exceed the minimum? Should root removal requirements be relaxed outside of the VMZ? What would be appropriate waterside planting berm designs? What thinning guidance should be provided? Should trimming or thinning ever be required for the lower waterside levee slope? Should all trees in VMZ <4 inches DBH be removed? 24

25 Criteria and Strategy Refinements When and where should we allow new vegetation on lower waterside levee slope? - Species - Levee properties - Effects on maintenance - Effect on channel capacity - Effects on federal programs eligibility - Environmental benefits and mitigation credit - Mitigation requirements if removed or thinned - Natural revegetation versus planting 25

26 2017 CVFPP and Conservation Strategy 2012 CVFPP Conservation Framework 2017 CVFPP Conservation Strategy 26

27 Thank You! ULDC and CVFPP Levee Vegetation Management Strategy are available at: 27