Presented by Fred Halterman, URS Jennie Agerton, URS

Transcription

1 Presented by Fred Halterman, URS Jennie Agerton, URS

2 What is Eco Friendly Culvert Design? Culvert design that: Maintains connectivity for aquatic organism migration Maintains connectivity for gene flow by allowing access to breeding and spawning areas Allows for natural stream transport It s a culvert the mimics the natural channel dynamics

3 Source: URS If you tell a fish to jump, it can t ask how high!

4 Connectivity for aquatic organism migration Ability to migrate allows species to find Food Mates Housing Shelter from predators

5 Source: URS Looks like a lot of work for a date!

6 Maintains connectivity for gene flow by allowing access to breeding and spawning areas Genetic diversity is essential for a healthy population When populations become isolated Gene pool is reduced Mutations are more likely Ability to adapt is lessened

7 Natural Stream Transport Streams change over time Dynamic system Sediments move through the system Streambanks migrate Watersheds change And in a lot of settings, very unnatural system changes occur.

8 This isn t eco friendly or landowner friendly! Look Familiar?

9 So, who cares?

10 This Guy Cares

11 These Little Guys Cares Chickamauga Crayfish Etowah Darter Source: URS Cherokee Darter

12 Georgia s Aquatic Diversity North American freshwater mussels historically reached their highest diversity in the Southeastern United States, particularly in Alabama (182 species), Tennessee (approx. 130 species), and Georgia (approx. 126 species). Georgia ranks third in the nation for the number of native freshwater fishes. Source:

13 This Guy REALLY Cares

14 Dollars and Cents According to GDNR, around 1.29 million resident anglers fish Georgia's diverse freshwater resources that include: more than 4,000 miles of trout streams, 12,000 miles of warm water streams wider than 10 feet, and 500,000 acres of impoundments Resident and non resident anglers currently spend about $569 million each year on fishing in Georgia. The economic effect of angler spending is about $1.5 billion. There are 10,649 jobs related to sport fishing in Georgia, which generates $15 million in state income taxes, and $19 million in state sales taxes. A major bass fishing tournament can have a $4 5 million economic impact on the local community. A championship event can have a $27 million economic impact. Sources: fish georgia

15 Aquatic Organism Passage (AOP) The objective of AOP is to shift traditional design methods in concepts that simulates the natural environment of aquatic organism (AO) travel for passage within the culvert.

16 Crossing Types New installations (including replacements) provides the flexibility to vary culverts Type Size Shape Alignment Bed material Retrofits are limited on options due to the constraints of existing field conditions

17 Eco Unfriendly Crossing Crossing width is much smaller than active channel Crossing slope is greater than 3% Crossing invert set at or above channel bottom Crossing not in alignment with stream channel Requires baffles or weirs to meet hydraulic design criteria Channel shows signs of instability upstream and downstream

18 Eco Friendly Crossings Crossing width at least as wide as active channel Crossing bottom is buried below streambed Natural bed material can accumulate Water surface blends smoothly upstream to downstream No obvious turbulent conditions

19 Types of Culverts Concrete Pipe Round or Elliptical Concrete Box Concrete Arch ConSpan Corrugated Metal Circular or Arch Plate (Bolt together) or Box Commonly used bottomless shapes. Bottomless Embedded Commonly used general shapes.

20 U.S. Army Corps of Engineers E. Culvert Restrictions for Perennial Streams: 1. The width of the base flow culvert(s) shall be approximately equal to the average channel width. Culvert(s) shall not permanently widen/constrict the channel or reduce/increase stream depth. Multiple pipe culverts may not be used to receive base flows. 2. Bank full flows shall be accommodated through maintenance of the existing bank full cross sectional area.

21 3. The upstream and downstream invert of culverts (except bottomless culverts) installed in perennial streams will be buried/embedded to a depth of 20% of the culvert height to allow natural substrate to colonize the structure s bottom and encourage fish movement.

22 E. Culvert Restrictions for Perennial Streams continued: 4. Culvert slope shall be consistent with average stream segment slope, but shall not exceed 4 percent. 5. Culverts shall be of adequate size to accommodate flooding and sheet flow in a manner that does not cause flooding of associated uplands or disruption of hydrologic characteristics that support aquatic sites on either side of the culvert. 6. Where adjacent floodplain is available, flows exceeding bankfull shall be accommodated by installing equalizer culvert at the floodplain elevation. 7. Unless specifically described in the PCN, use of undersized culvert to attain stormwater management or waste treatment is not authorized. 8. See Appendix D for additional culvert design information.

23 Passage Barriers Organisms need mobility to seek food, find shelter, avoid predators, and reproduce A culvert becomes a barrier to AOP when it poses a disconnect in the natural stream transport A barrier poses conditions that exceed the organisms physical capabilities

24 Excessive velocity Lack of depth Perched culvert outlet Lack of depth outlet pool Obstructions within pool Entrance velocity/apron Types of Passage Problems Velocity barriers Culvert set a too steep slope Low roughness Length of culvert x Velocity > fish abilities Lack of outlet pool depth Jump height to pool depth ratio 1:15 Low roughness Length of culvert x Velocity >fish abilities

25 Common AOP Barriers Excessive water velocities induced by an undersized culvert Drops at culvert inlets or outlets Physical barriers such as weirs, baffles, or debris caught in the culvert barrel Excessive turbulence caused by the constriction of the crossing Low flows through a culvert that causes a disconnect in continual stream flow Common Barrier Types: Jump barrier Velocity barrier Both Jump Barrier Or Both

26 Aquatic Organism Biology Physical capabilities to accommodate different modes of travel Aerobic (low intensity activity) Anaerobic (shorter, high intensity activities) An aquatic organism can fail to pass through a culvert for many reasons but the main reasons are barriers that require exertion beyond physical capacity.

27 Hydrology AOP movements are related to the season and stream flow conditions Culvert design should provide AOP for a range of hydrological flows that correspond to the timing and movement for the AO in their natural environment High passage flows, Q H, represents the upper bound of the flow which the fish can pas without stream turbulence. Low passage flow, Q H, is the lowest flow which a fish can pass Q H and Q L depend on the hydrologic region Hydrologic Data Flood Control vs. Fish Passage Flood control flows i.e. Q25, Q50, Q100, and Q+ Fish passage Q L <Qpass<Q H

28 Geomorphology and Stream Stability Think of a culvert as a rigid structure in a dynamic environment Channels are continually evolving and steam adjustment potential must be addressed Design that does not account for a dynamic system could detrimentally affect the stream and habitat Geomorphic and hydraulic factors affect stream stability. Look at: Channel stability Scour Line, In Situ Sediment Size for Bed load, Active Channel Width and Depth Degradation Perched Terraces, Head Cutting, Exposed Roots, Culvert/Bridge Scour Restoration concepts to achieve natural stability

29 Design of New Installations The state of the art in AOP is the use of Stream Simulation. Using Stream Simulation opens up a full range of culvert characteristics in design so that the culvert interior can become part of the natural stream. Application of Stream Simulation is a multi team effort. Design team would consist of biologists, geomorphologists, environmentalists, and ENGINEERS. Mainly two simulation methods are used: USFS Stream Simulation (2008) FHWA HEC 26 (FHWA 2010a) Both methods apply to closed bottom and open bottom culverts Or: No slope design simplified method Retrofits Hydraulic design matching culvert hydraulics to fish swimming abilities Or Stream Simulation

30 USFS Method Uses a reference reach to measure stream stability Transport sediment and debris should not be constrained or accelerated inside the culvert. Mimics natural channel transport Uses bankfull flow for a good estimator of a stable alluvial channel Critical that channel inside structure be at least as wide as the bankfull width Assumes culvert design does not alter the forces on the stream bed Bankfull width and the reference reach are the main measures for the stream simulation. The design process addresses: Alignment and profile Channel bed cross section and materials Culvert dimensions and type Bed mobility and stability Risk factors (or measure for potential causes of failure)

31 HEC 26 Method Based on streambed stability not bankfull width Based on capital cost for AOP evaluation 5 primary design variables Peak design flow Q X for various X year recurrence intervals (i.e., Q 25, Q 50, and Q 100 ) High passage design flow, Q H Low passage design flow, Q L Bed material characteristics (D X bed material particle size % passing by weight) Permissible shear stress, P, of the bed material

32 Five Fundamental Test Parameters Applied to Simulation Does culvert pass peak design flows? Is the bed material in culvert stable (I = O for Q H )? Is the bed material stable for Qpeak? Is velocity within culvert consistent with the upstream and downstream velocities of channel for Q H? Is flow Q L consistent with the upstream and downstream channel depths? The 5 tests are conducted by a 13 step design procedure

33 HEC 26 Logic

34 Stream Simulation Acceptance Both procedures USFS and HEC 26 test for stream stability If the design does not alter the hydraulic parameters of the channel, then the design can be presumed not to alter the forces experienced by the AO.

35 No Slope Culvert Design Culverts embedded in channel bottom Placed at very little or no slope Short lengths

36 Hydraulic Design Approach Match hydraulics to AO abilities Targets certain AO s fish usually Least favored design approach Usually used in culvert retrofits Baffles, weirs, fish ladders are commonly used Angled Baffles Alternating Baffles

37 Retrofit Options Culvert capacity must be checked for retrofit Retrofitting is likely to be a series of compromises to provide acceptable AOP, while maintaining hydraulic capacity Hydraulic capacity? Use additional overflow culvert above stream Line culvert (check velocity) Baffles, sills and oversized bed materials used for inside the culvert to reduce velocities and increase depths for AOP

38 Stream Simulation for Retrofits Streambeds are created within the culvert Bottom of non circular culvert is non structural Existing culvert conveyance capacity exceeds design flow Culvert width exceeds or is close to active channel width Structural changes to the structure can be made Typical constraints within the culverts Bottom of non circular culvert is a structural supporting member and can not easily be altered Existing culvert conveyance capacity doesn t convey the design flow Piers or supporting structures are scour critical Entrance constraints

39 Profile Adjustments The upstream and downstream channel bed profiles may be adjusted to impact hydraulic conditions within the culvert Typical techniques include grade controls using: Boulder weirs concrete sills Log sills Rock Jump Pool Weirs

40 Construction Allowable seasons for in stream network Protection of stream banks, vegetation, and aquatic organisms Consideration for placement of bed material for embedded culvert Culvert size (height) to provide for mechanized equipment or manual labor for access within culvert during construction (bed material placement, sealing of culvert joints, etc.)

41 Post Construction Maintenance inspections Passage monitoring to see if AOP goals were achieved Bed material monitoring This Not This!

42 Wrap up Ideally a new structure/culvert should not change existing conditions The cross sectional area of the stream should not be changed Channel roughness should remain the same Stream fluvial processes should continue Some retrofit problems may be correctable but may be a partial barrier during some flows or some life stages Use baffles and weirs inside culverts with caution Use downstream hydraulic control to improve conditions through the culvert Hydraulic design criteria is the goal for culvert retrofits

43 For Further Questions and Discussion Contact: Fred Halterman