Forest Service AOP Meeting Objectives of Stream Simulation: Examples and Talking Points

Transcription

1 Forest Service AOP Meeting Objectives of Stream Simulation: Examples and Talking Points Traci Sylte, P.E. Hydrology/Fluvial Geomorphology Lolo National Forest

2 Is It True? Are Road Crossings a Dam with a Little Hole?...

3 Road-Stream Crossing Objectives: A Win-Win Scenario Maximize Structure Life Minimize Maintenance Optimize Safety Provide for Species Passage Provide for the Stream Function and Water Quality

4 Overview: Provide Examples and Talking Points of the Essentials to Meeting Primary Stream- Road Crossing Objectives Designing By Stream Type Designing Dimension, Pattern, Profile Principles and Processes For Structures Green Considerations

5 Simulate adjacent natural channel Premise: If the stream channel through the crossing simulates the dimensions, character, and processes of the adjacent natural channel, it will present no more of an obstacle to movement of organisms than the natural channel.

6 Big Picture: Narrowing Watershed Processes Large Scale Processes Floods Fire Mass Failures Debris Torrents Wind Throw Drought Organism Life Cycles Nutrient Cycling Cumulative Human Impacts What it Means to Crossing Design 1. Water Transport 2. Wood Transport 3. Sediment Transport 4. Species Passage

7 Base Flow Bankfull (normal high) Flow Water Transport Flood Flow

8 Multiple Channels: Base, Bankfull, Floodplain

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10 Water and Scour High Velocity Scour 1979 Siegel Ck, LNF 1998 Siegel Ck, LNF

11 Wood Transport Stream Function energy dissipation, grade control Habitat Nutrient Cycling Structure Failure / Maintenance

12 Sediment Transport

13 Bars Upstream of Structures: An Indicator of Backwater Conditions

14 Okay Simulate: but what width, depth, profile, substrate

15 Stream Simulation Design: 4 Primary Components 1. Geometric Alignment 2. Channel / Structure gradient 3. Bed width and shape 4. Bed material design & channel forms

16 The Channel: Dimension, Pattern, Profile From Rosgen 1994

17 Some A Stream Types A1 - Avalanche chutes, headwaters, faults, bedrock areas A2 -Steep -Well entrenched -Low width/depth ratio -Step-pools, cascades, waterfalls -High energy A4 Montgomery & Buffington Source or Transport Streams Aa+

18 Some B Stream Types B3 - Moderately steep to gently sloping terrain and basin types. -Moderately entrenched -Transport dominated (ripples and rapids) -Width/depth ratios greater than 12 -Moderate slopes, generally 2-4% -Streambank erosion rates are low and stability is typically great. - moderate sinuosity -Relatively Stable -Plane-bed or Step-pool B3 B2 B4 Montgomery & Buffington Transport Streams

19 Some C Stream Types C4 -Narrow to wide valleys with well developed floodplains - Slopes, generally less than 2% - Stability dependent on stream banks and vegetation C4 C4 - Reconstructed - Sinuous - Riffle-pool dominated - Width/depth ratios greater than 12 Montgomery & Buffington Response Streams C4 altered with berm

20 Some D Stream Types - Multiple channels, braided, multiple bars. -Steep depositional fans, glacial troughs, deltas, outwash areas, disturbed valley streams - low sinuosity -High bank erosion -Relatively Unstable - channel slope generally similar to valley slope D5 D3 D4 D4 Montgomery & Buffington Response Streams

21 Some E Stream Types E6 -Very high sinuosity and low gradient, except where altered or in steep mountain meadows - only slightly entrenched/dominant floodplain - most efficient transport per unit width of all stream types -Highly stable, but very sensitive to disturbance and vegetation removal -Width/depth ratios less than 12 E5a Montgomery & Buffington Response Streams E5 E4 E4 altered by grazing

22 Stream Simulation Bankfull Width Barnard

23 Bed Width and Shape Culvert bed Shoulder (or bankline if continuous) Channel margins Band 10 ft low flow channel

24 Construction - Stream reconstruction 4.5%

25 Construction - Stream reconstruction

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27 Culvert Elevation Culvert Rise Range of possible bed elevation from long profile analysis (Range) Bed profile elevation 50% D 30% D By simple math Culvert Rise > 5 x Range

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29 Planform...Meandering Tendency Like a two year old child, a river can t sit still, Mount, 1995 Bending is a central tendency.it s all about physics.

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31 Planform Considerations: Designing for Bends 1. Avoid Sinuous Channels 2. Locate Crossings on Straight Sections 3. If Straightening is Necessary - Do Not Straighten the Stream Longer than its Natural Meander Wavelength (Don t make the distance between bends or pools longer than the natural ranges) 4. Accept Small Skews and Reinforce Banks If Necessary 5. May Need to Perform Channel Restoration to Recreate Natural Geometries Differs by Stream Type ** Work Within the Natural Meander Geometry of Your Stream Type!!!!!

32 Gradient Considerations Crossing replacement accommodated the bankfull channel dimensions, but quickly filled again because it is located at a channel grade change between a C4 and D4 channel type. Moving the road 200 feet upstream to a B4 channel type would have transported all material efficiently through the crossing.

33 Gradient Considerations Roads are often located at stream gradient changes. Look for these slope breaks and evaluate what it means to sediment transport, backwater, aggradation, and degradation. Gubernick, Furniss, and Clarkin, in press

34 Degradation Downstream Hogback Creek Pipe Removal Before/After Longprofile, Elevation (ft) As Built Pre-Construct Culvert/Road Bridge Bottom Debris Distance (ft)

35 Remedy to Degradation at Outlet

36 Bedform and Substrate

37 Channel Bed Form and Substrate

38 Construction of Steps Finished profile 6. Bed material to grade 5. Top step pool rock 4. Additional bed material 3. Step pool footer 2. Bed material to final grade 1. Sub-grade access pad

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40 Other Substrate Considerations - Mimic natural substrate sizes & distributions - Failure to do so can result in: Subsurface Flows Scour of Substrates -Account for Armor Layer & assure fines are incorporated.

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42 Other Talking Points

43 Floodplain Connectivity: Unconfined channel Hydraulic / Stability analysis when floodplain conveyance high Increase culvert width Improve inlet contraction Add floodplain culverts (when either Q10 floodplain > 4 x BFW?) Add road dips Increase bed material size

44 This is an E4 stream type where the culvert spanned the bankfull channel width, but did not allow for floodplain flows. It failed periodically requiring both road and culvert maintenance until a bridge structure was installed.

45 Landscape Position is Very Important Possible D,E,F,G Alluvial Fans Deltas (lakes

46 Lightening Creek

47 Bankfull Identification - Responsible for general channel shape and size - Transports more sediment over time than any other discharge - Occurs on average every years - Common pseudonyms: active channel, ordinary high water mark, and Q2

48 Bankfull Indicators Top of Flat Depositional Areas Change in vegetation Slope Breaks Change in particle sizes between bed, banks, and floodprone area Bank undercuts, root, and scour lines Stain or lichen lines on boulders tls 5/7/03

49 Bankfull Indicators seek local expertise verify local indicators! Is it? Is it not?

50 Lolo Creek Boulder Clusters 1980 s Stability in Substrate Design Lolo Creek Boulder Clusters 2005

51 A Principle of Scour & Settlement Protection Settlement and 1 Mobility Process by Un-Protected 2 Downstream 3 Scour Structure Design For Stability Each of these will provide stability

52 Structures & Principles We must work with channel hydraulics with our structures. Check structures impede velocity and bedload transport, often flank and/or scour, and over-widen channels Bad, bad, bad

53 Good, good, good

54 DESIGNERS: Reality Check!!!!!!!! Average Stream Velocities (Spring Runoff or Slightly Greater) Mountain streams ft/s. Valley streams ft/s.

55 Critical Velocities for our fish: 4-5 fps (We shouldn t be surprised) Chinook Coho Steelhead Cutthroat Brown Trout Grayling Whitefish HEALTHY ADULTS Cruising Speed Sustained Speed Darting Speed Velocity (feet/second) M. Bell 1989

56 Lolo NF Leaving a Site Green

57 Geomorphic and Analytical Approaches to Stream Rehabilitation Design and Reconstruction Have Taught Us A Lot. Incorporate them.

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59 Design Advancements Bad Riprap Good Riprap Good Riprap Design: 1. Used where excluding lateral stream movement is not a detriment or is not feasible 2. Designed irregular bank line and rock protrusions dissipate energy and create habitat niches at multiple flow levels 3. Only protects to a designed flood level, often bankfull or Q100 are used 4. Incorporates vegetation and creates habitat 5. Of course, has necessary size classes and configuration to remain stable

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61 Is It True? Are Crossings a Dam with a Little Hole?... IT DOESN T HAVE TO BE!

62 Acknowledgments for Slides and Photos Lolo National Forest et. al. Shane Hendrickson, R1 John Casselli, R1 John Kattel, R1 Pete Odegard, R1 Rod Blessing, R1 Chad Bensen, R1 Bob Gubernick, R10 Kim Johansen, R6 Dan Cenderelli, R6 Thomas Dunklin