Options looking forward for sediment management in the Alameda Creek Flood Control Channel

Size: px

Start display at page:

Download "Options looking forward for sediment management in the Alameda Creek Flood Control Channel"

Anthony Pope
6 years ago
Views:

1 Options looking forward for sediment management in the Alameda Creek Flood Control Channel Lester McKee Alameda Watershed Council Annual Conference 1

2 Alameda Creek Flood Channel Large alluvial fan and floodplain complex Aerial photo of the urbanized alluvial fan and flood control channel from Niles Canyon to the Bay 2

3 Alameda Creek Flood Channel 12 mile long Flood Control Project Looking upstream in the lower fluvial reaches of the flood control channel 3

The Flood Control Channel Flood control channel completed 1975 Straightening, widening, regrading, and partially rip-rapping 12 miles Maintenance manual provides guidelines to maintain the 100-year

4 The Flood Control Channel Flood control channel completed 1975 Straightening, widening, regrading, and partially rip-rapping 12 miles Maintenance manual provides guidelines to maintain the 100-year flood capacity 52,000 cfs at the junction with Dry Creek, FEMA 1975 Sediment is periodically removed at great cost so that nowhere shall the mean elevation in a reach exceeds 2 feet above design grade. Fremont area during the 1955 flood, prior to construction of the flood control channel (source: Young 1962). 4

5 Dredging History of Alameda Creek * Provisional Peak Flow at Niles (cfs) * Maintenance (yd3) 200, , ,000 50, ? Year 5

6 The Permitting Problem Revised guidelines Take into account threatened and endangered species and habitats within creeks Maintenance procedures must achieve both flood control and environmental criteria Sediment removal Impact on the creek itself Proper disposal A resource for future use Permits will no longer be issued without further investigations and improved practices 6

7 Two Conceptual Management Options Reduce and manage water and sediment supply from upstream (nonpoint source solutions) Multi-agency and private landowner effort Facilitated by watershed goals Change the way sediment is managed in the channel (reach specific solutions) **Ultimately both solutions may have benefit 7

8 The Santa Cruz - Example 1955 flood destroys part of the town 8

9 Corps project Straightening Levees Below grade Channel substrate Flat Shallow Sandy stream bed 9

10 Early 1970s Annual floods deposited sediment during the 60s and early 70s reducing capacity from 100 y to 30 y Corps argued that sediment removal was best ongoing solution City argued cost prohibitive and permits would be too challenging to obtain Meanwhile FEMA remapped floodplain 10

11 1982: Flood Channel bed scour Soquel Ave bridge central pier lowered 18 feet Earlier estimates assumed a fixed bed Subsequent studies revealed backwater effects and aprons stopping scour 11

12 Late 1980s Corps HEC-6 study found that scour providing for 100 y but without the required 3 ft freeboard Conceded that annual sediment removal was not most cost effective 12

13 1990s City and Corps developed a floodwall and levee raising plan Project completed in 2001 Channel constrictions causing sedimentation removed 13

14 River Enhancement plans (1990, 2003) City, resource agencies and Corps agree on vegetation and habitat management plan City monitors and removes vegetation for roughness design specs Channel capacity is tested using HECRAS as part of adaptive management Ripping operations to prevent root armoring of the channel bed Vegetation is kept in an early succession state with limited to vegetation width and stem diameter by maintenance (scrub willow alder cover) The bankfull channel is maintained as part of the river vegetation management 14

15 Outcome Multi-stage channel More confined deeper channel Gravel cobble substrate Greater hydraulic complexity Biological habitat value Most of the channel has Over-story cover Deep pools Salmonid rearing Occasional instances of spawning in lower river 15

16 Outstanding issues Corps claims that some sediment removal is still necessary City disagrees. No finalization of O & M plan Post-Katrina Corps vegetation management is calling for removal of vegetation planted on backside of the levee that was part of the Corps levee raising project City is undertaking studies 16

17 But there are other examples San Lorenzo provides an example of what is possible when multiple agencies objectives are met, however: Smaller in area Steeper gradient Wetter system Flows to ocean Not managed for water supply 17

18 Wildcat, Richmond, Contra Costa 18

19 Guadalupe River, San Jose, Santa Clara 19

20 Other examples Russian River, Sonoma County Trinity River, Northern California 20

21 Previous and ongoing Scientific and Engineering Studies in Alameda Sediment source analysis in the upper watershed Reconnaissance (Watershed Sciences) Sediment budget for the middle reaches (SFEI) Review of sediment gaging (SFEI) Modeling sediment transport processes in the Flood Control Channel (DHI ongoing) Studies of sediment grain size in the Flood Control Channel (SFEI ongoing) 21

22 Previous and ongoing Scientific and Engineering Studies in Alameda Modeling and engineering design of the lower three miles in relation to saltpond restoration and levee breach (PWA ongoing) Studies of fine and coarse sediment load from small tributaries on the Alameda Fan (SFEI/ Pearce et al ongoing) Historical Ecology of Alameda Creek (SFEI / Grossinger et al ongoing) Spartina monitoring plan to support saltpond restoration (SFEI / Grenier ongoing) 22

23 Some key findings from the SFEI work 23

24 Sediment Budget Overall Watershed Comparison for Recent Period ( ) Sediment Yield Area Metric t/year % of Total ADLL at Verona Gage 104, Alameda Creek near Welch Ck Gage 3,400 2 Arroyo de La Laguna Study Reach 8,400 5 Alameda Creek Study Reach Ungaged areas 47, All Areas above Niles Gage 164,000 Alameda Creek at Niles Gage 156,000 24

is 5,900 tonnes/yr, or 4% of the load passing Niles gage 4.0 3.

25 Dry Creek Dry Creek (10 mi 2 ) is 1.5% of the total Alameda Creek watershed area Average sediment discharge is 5,900 tonnes/yr, or 4% of the load passing Niles gage Dry Creek Fan Perimeter 3.0 Dry Creek confluence Relative elevation (m) Dry Creek fan

26 Sediment in the Flood Control Channel D50: mostly fine medium sand Some samples >50% cobble 86% is >62.5 micron 26

27 Options looking forward Further geomorphic, engineering studies, and modeling to inform flood control channel management options Further data collection in strategic locations to learn about sediment transport and supply to the channel Watershed stewardship to reduce or store water and sediment supply during large floods Facilitated by watershed goals? Wildcat Creek 27

28 Geomorphic and sediment related analysis for Alameda Creek (SFEI): Dr. Lester McKee, Sarah Pearce, Jen Hunt and others Restoration Design Group: Roger Leventhal, P.E. Watershed Sciences: Laurel Collins CEMAR: Gordon Becker DHI Water and Environment, Inc. 28

29 SFEI team study plan and progress Long term goal: Develop a sediment management plan that reduces costs and permitting, while maintaining flood capacity and maximizing habitat benefits Geomorphic assessment Support for improved maintenance practices 29

30 Geomorphic study questions What are the rates and locations of recent sediment deposition? What is the relationship between low-flow channel and bankfull discharge? How has the low flow channel evolved through time? What in-channel features are causing sediment deposition? Does the channel bed scour during floods? 30

31 Support improved maintenance practices Review Santa Clara Valley Water District s 2009 Open Channel Hydraulics and Sediment Transport Design Manual Field visit to San Lorenzo River, Santa Cruz Verify the current channel capacity in relation to the existing operations and maintenance manual 31

32 Support Improved maintenance practices Review 10 years of existing studies and assimilate recent SFEI team observations including HE of the channel Evaluate current level of wildlife support and likely future support in relation of planned or possible future management Evaluate sediment reuse options Final report: A qualitative analysis of interim management options Enhanced vegetation management and targeted desilting operations to reduce wildlife impacts and enhance channel configuration to a more desirable state Preliminary commentary on future conceptual design/management options including recommendations for further investigations 32

33 33

34 Stonybrook Creek Questions How much coarse sediment is contributed? What are the primary processes of sediment supply and delivery? How is sediment affecting fisheries and infrastructure? Methods Field reconnaissance utilizing GIS-based terrain mapping and aerial photograph analysis 34

35 35

36 Zone 7 SFEI studies Support improved modeling for design and compliance purposes and decisions about future operations and maintenance of its facilities AMP Flow gage 36

37 Study Components Determine the flow of water and sediment into and out of mainstem Arroyo Mocho Determine characteristics, rates, and causes of sedimentation Develop a sediment budget for the study reach as a tool for clearly communicating the main sources and processes affecting the function Map and characterize channel modification and mitigation opportunities based on a comparison of historic and modern channel function Communicate findings to the broader community within the Alameda Watershed Council 37

38 Take home messages Business as usual on the Alameda FFC may not be most cost effective or feasible There are examples of alternative management styles Studies have started to explore options It will take a coordinated agency effort with all parties committed to a future vision to reach a new management paradigm for Alameda FCC Santa Cruz experience took 30 years Alameda might be a smoother process? 38

May 7, Roger Leventhal, P.E. Marin County Public Works Laurel Collins Watershed Sciences

May 7, Roger Leventhal, P.E. Marin County Public Works Laurel Collins Watershed Sciences May 7, 2013 Roger Leventhal, P.E. Marin County Public Works Laurel Collins Watershed Sciences Background Funded in 2009 under EPA 2100 Grant for $30k and managed by SFEP Project Goals: Update original