Instream Habitat Enhancement

Transcription

1 Instream Habitat Enhancement Jeremiah D. Bergstrom, CLA, RLA, ASLA Principal-Water Resources 850 Bear Tavern Road, Suite 104 Trenton, NJ Phone: x101

2 Instream Habitat Enhancement Projects that include the placement of wood and stone structure into the stream channel in combination with appropriate plant and/or bioengineering materials for the purposes of enhancing habitat for fish and other aquatic organisms 2

3 Why habitat enhancement? Stream profile and cross section has been altered/straightened due to anthropogenic activities and no longer exhibits habitat complexity suitable for supporting a diverse aquatic ecosystem Embedded substrate does not currently provide suitable habitat for many aquatic invertebrate species Stream reach has incised banks which do not provide instream cover or suitable fish habitat 3

4 Key Design Principles The development of aquatic habitats requires that streams actively experience sediment flushing and depth variations through scouring action. Scouring causes local movement of instream sediments with the primary goal of shifting bedload material a short distance downstream. This shifting of sediments creates the beginning of a meander. As meanders develop in a stream system, gradient decreases and current velocities and sedimentcarrying capacity are reduced. These effects provide for the development of riffles, deeper water (pools) and improved instream cover enhancing aquatic habitat. Project designs should meet the broadest habitat requirements that can be encompassed while still meeting basic objectives and addressing any target species needs. Ecosystem diversity is important. Maintain fish passage. 4

5 Enhancement Objectives Create deeper water reestablish pool habitat Narrow channel width Remove sediment by flushing action reestablish riffles Add cover for fish creating hiding or resting areas Add substrate and food for aquatic organisms throughout addition of woody debris 5

6 Habitat Enhancement Techniques Boulder Placement / Boulder Clusters Revetments and Cover Logs Cribbing Deflectors Small Dams and Channel Control Structures 6

7 Boulder Placement / Boulder Clusters Boulder clusters are groups of large rocks placed in a stream to improve habitat, and create scour holes and areas of reduced velocity. Placing the boulders in the stream creates eddies or vortices in their wake, which create overhead cover for fish by partially diffusing sunlight. Boulder clusters can also generate scour that cause pockets of deeper water to develop, which adds to the physical diversity of the stream (Fischenich and Seal, 1999). 7

8 Boulder Placement / Boulder Clusters Boulders can be used in most stream habitat types including riffles, runs, flats, glides and open pools, but are most effective in wide, shallow streams with gravel or rubble beds. In deep streams, they can provide cover and improve substrate. 8

9 Boulder Placement / Boulder Clusters Evaluations of fish habitat improvement projects have shown a high variability in the benefits of instream boulders. This variability is due to differences in fish seeding levels, species and ages of fish, season of year, the design of the project, time since implementation, and sampling method (Fischenich and Seal 1999). Group placement of boulders is most effective, but individual boulders may be effective in small streams (FISRWG, 1998). 9

10 Boulder Placement / Boulder Clusters Design Considerations The primary design considerations for boulder clusters are a) the number, configuration, and location of the structures, and b) the size of the boulders needed for stability. The hydraulic impacts of the boulders should also be ascertained when habitat benefits must be quantified or the potential exists for adverse impacts due to increased velocities or water surface elevations. For boulder clusters, the greatest benefits are realized in streams with average flows exceeding 2 feet per second. Boulders should not be used near banks susceptible to erosion. The use of boulder clusters is generally limited to streams with coarse gravel (or larger) substrate. It is not recommended for sand bed streams because the boulders have a tendency to become buried. 10

11 Revetments and Cover Logs Revetments and cover logs include the use of brush and woody material secured to the streambank to provide overhead cover for fish and support insect and other fish food organisms. These structures can provide limited streambank protection. Various materials and techniques can be used, but must be securely anchored to avoid becoming dislodged. 11

12 Revetments and Cover Logs Suitable for use in lowgradient stream bends or meanders where open pools are already present Can be used in combination with other techniques Brush and woody materials maximize surface area for both terrestrial and aquatic insect habitat Can be labor intensive to install 12

13 Revetments and Cover Logs Root Wad Cedar Tree Revetment Cover Log 13

14 Revetments and Cover Logs 14

15 Revetments and Cover Logs NOTE: Brush layering is a bioengineering technique that can be used in combination with tree revetments and cover logs 15

16 Cribbing A cribwall is a live log wall, built cribstyle, to protect eroding banks. Vegetation is planted between the logs used to build the wall. The vegetation reduces stream velocities as well as provides cover and shelter for fish. The root structure of the vegetation strengthens the material within the crib. 16

17 Cribbing This technique is useful when slopes are too steep for other techniques of stabilization and there is no room to cut back the slope. Cribwalls are also effective to prevent toe erosion by scouring. Cribwalls do not need to be built up the entire bank. Another bioengineering technique can be installed on the upper bank. Cribwalls should be used for walls four foot high or less and not longer than 20 feet. For successful vegetation establishment ensure that the cuttings are dormant and are installed soon after harvest. The branches should not be allowed to dry out. The cribwall must be constructed during low water period. 17

18 Cribbing Live Timber Crib Wall 18

19 Deflectors Deflectors constrict and divert water flow so that stream meanders and pools are formed by scouring and relocation of fine sediment and gravel 19

20 Deflectors Can be made of logs and/or stone and can rise 6 to 18 inches above normal flows, but should always be less than streambank height. Low-flow stream width can be narrowed up to 70-80% between the tip of the deflector and the streambank to achieve desired results. Stream velocity is reduced as scouring forms a pool extending from the apex of the deflector to the far bank. 20

21 Deflectors Deflectors are built singly to protect an eroding bank, or in pairs to narrow the stream channel. They are placed in a series, positioned alternately, on one bank and then the other to keep the current sweeping swiftly in a natural winding pattern. In nature, pools and riffles normally are repeated every 5 to 7 channel widths; therefore, the distance between deflectors should be at least seven times the average stream width. Deflectors may be constructed entirely of rock, or rock and wire combinations (gabions), or rock framed with logs. Build deflectors in a triangular shape, with the tip pointing downstream and angling out toward the channel. Adjust the angle (usually about 30 degrees between the bank and the deflector) to guide the current into midchannel at a suitable speed. Check the path of the current by throwing a float into the water upstream from the deflector. If the float hits the opposite bank, modify the size or angle of the deflector until the float remains in mid-channel. Deflectors built at an extreme angle (pointed more across than down stream) or too long (more than one half the channel width) may cause erosion on the opposite bank or catch floating debris. Improperly built deflectors receive greater water pressure and may be damaged by floods. Build deflectors low with only a few inches above the water surface at the offshore tip and tapered upward toward the bank. Design deflector height to allow high flows to pass over the top of the structure. Remember, deflectors should guide the current, not dam it! Avoid building deflectors in riffles. Preserve natural riffle areas from any type of disturbance or construction. They are important fish food production and spawning areas. 21

22 Deflectors Single-Wing Deflector Deflector and Cover Log 22

23 Deflectors Single-Wing Deflector & Cover Log Double-Wing Deflector 23

24 Deflectors Double-Wing Deflector NOTE: Double-wing deflectors create midchannel pools through scouring action in shallow sections of streams Single-Wing Deflector & Cover Log NOTE: A cover log ensures bank stability where suitable boulders, tree stumps, or stable banks are lacking 24

25 Small Dams and Channel Control Structures Small dams or structures across a stream can be used to create pools or deeper water through scouring action in shallow sections of streams. In continuous, steep gradients, the short, upstream break in gradient also provides resting area, often holding more fish than does the deeper pool below. The quiet water above the structure and the edges of the pool below also act as a trap for organic material used as food by stream invertebrates. 25

26 Small Dams and Channel Control Structures Any channel control structure requires a detailed investigation of the stream hydraulics and morphology. An intensive design process should be used to thoroughly understand the problem and propose structures that meet project goals and objectives. It is critical to understand the impacts of proposed structures to upstream and downstream areas. Natural channel design principles should be applied when considering the location of channel control structures, including identification of tributary locations, changes in channel evolution type and other significant hydrologic or geomorphic features. 26

27 Small Dams and Channel Control Structures Wedge Dam 27

28 Small Dams and Channel Control Structures Boulder Cross Vane 28

29 Small Dams and Channel Control Structures Log Cross Vane 29

30 Small Dams and Channel Control Structures K-Dam 30

31 Small Dams and Channel Control Structures W-Weir A W-weir is made of very large rock in the shape of a W. The edges of the W are anchored into each bank at the top of the bank or the "bankfull" elevation. The bottom or upstream points of the W are at the stream bottom or thalweg elevation and the top point of the W on the downstream side is at an elevation 1/2 way between the other two. The design was created by David Rosgen of Wildland Hydrology. A W-weir allows river flow to pass through a segment of stable cross section while providing grade control and stream bank protection. 31

32 Small Dams and Channel Control Structures W-Weir SOURCE: Dimondale, Eaton County, Michigan Dam Before Restoration W-Weir After Restoration 32

33 Small Dams and Channel Control Structures Step Pools 33

34 Summary Understand the specific needs of the aquatic species of concern and provide for the broadest range of habitat enhancement Maintain fish passage at all times Use natural materials that are readily available and appropriate to the geologic region and habitat area you are working in Understand the impacts structures will have on upstream and downstream areas Securely anchor all materials appropriately 34

35 Additional References British Columbia, Ministry of Agriculture, Food and Fisheries. Constructued Ditch Fact Sheet, Bio-engineering Techniques. Fischenich, C., and Seal, R Boulder Clusters. U.S. Army Engineer Research and Development Center, Vicksburg, MS. FISRWG Stream Corridor Restoration: Principles, Processes, and Practices. Federal Interagency Stream Restoration Working Group, Houser, D. and Lutz, K Fish Habitat Improvement for Trout Streams. Pennsylvania Fish and Boat Commission Kelly, F Restoration of Urban Streams. United States Department of Agriculture, Massachusetts Nonpoint Source Pollution Management. Boulder Clusters and Rock Riffles Fact Sheet. North Carolina State Cooperative Extension. Fact Sheet Number 4 Using Root Wads and Rock Vanes for Streambank Stabilization. Rosgen, D. The Cross-Vane, W-Weir and J-Hook Vane Structures Their Description, Design and Application for Stream Stabilization and River Restoration. Wildland Hydrology, Inc. Seehorn, M Stream Habitat Improvement Handbook. USDA Forest Service, Technical Publication R8-TP 16. Virginia Cooperative Extension. Landowner's Guide to Managing Streams in the Eastern United States. 35

36 Case Study Pike Run Habitat Enhancement and Restoration Project 36

37 Project Overview This restoration effort proposed instream habitat enhancement and floodplain wetland habitat enhancement through the placement of in-stream structures and native plantings in portions of Montgomery Park. The project team conducted detailed preliminary analyses including stream cross section surveys in accordance with Rosgen stream classification methodologies and have proposed a restoration scenario focusing on improving instream habitat within an approximately 1000 linear foot segment of Pike Run. In addition, large areas of floodplain wetlands currently mowed by the Township and frequented by Canada Geese and other nuisance wildlife populations have been planted with native meadow and woodland species to further expand and enhance the riparian buffer along the stream. 37

38 Project Objectives The stream substrate in the target section of Pike Run consists of both bedrock and embedded cobbles. The embedded cobbles and bedrock do not currently provide suitable habitat for many aquatic invertebrate species. The reach also has incised banks which do not provide instream cover or suitable fish habitat. The development of aquatic habitats requires that streams actively experience sediment flushing and depth variations through scouring action. Scouring causes local movement of instream sediments with the primary goal of shifting bedload material a short distance downstream. This shifting of sediments creates the beginning of a meander. As meanders develop in a stream system, gradient decreases and current velocities and sediment-carrying capacity are reduced. These effects provide for the development of riffles, deeper water (pools) and improved instream cover enhancing aquatic habitat. The objectives of the project team are to increase the number of riffled areas and pools within the existing stream channel suitable for invertebrates as well as provide more in-stream fish habitat and cover along stream banks. 38

39 Pike Run - Existing Stream Conditions 39

42 Pike Run Study Area Riparian Planting Location in Park Harlingen Road Existing Stream Segment for Structures 42

43 Pike Run Original Design 43

44 Pike Run Original Design 44

45 Pike Run Final Design To achieve the stream enhancement objectives, the project proposes the use of a series of single-wing deflectors and cover logs. These structures constrict and divert water flow during normal flow conditions so that stream meanders, riffles, and pools are formed by scouring and relocation of fine sediment and gravel. The finished structure height of the deflector structures will not be greater than 6 inches above normal flow conditions as to minimize any increases in scour action during storm events while still providing resting and holding areas for aquatic species. Structures will be constructed of logs a minimum of 14 inches in diameter, pinned together at a 90 degree angle and placed at a degree angle to the streambank. The space inside the structure will then be filled with large cobbles or boulders. Waters overtopping the structure will be directed toward the center of the stream and away from streambanks, creating meanders, pools, and riffles within the existing stream bed. To prevent sloughing and reduce current erosion on opposite streambanks, cover logs with stream bank plantings are proposed. In addition to providing protection against potential streambank erosion, the logs and plantings provide addition cover and further enhancement to aquatic habitats in the stream reach. 45

46 Pike Run Final Design 46

47 Pike Run Instream Habitat Enhancement Construction and Installation Photos 47