Vegetation Management in River Restoration - PowerPoint PPT Presentation

1 / 31
About This Presentation
Title:

Vegetation Management in River Restoration

Description:

... streams, Canadian J of Fisheries and Aquatic Science, 58, 282-292, 2001 ... Resisting rapid bank slumping (up to some bank height) slow channel migration ... – PowerPoint PPT presentation

Number of Views:49
Avg rating:3.0/5.0
Slides: 32
Provided by: tdu5
Category:

less

Transcript and Presenter's Notes

Title: Vegetation Management in River Restoration


1
Vegetation Management in River Restoration
  • Floodplains
  • Riparian zones
  • Channels

2
Readings for next week
  • Brooks, A. P. et al. The long-term control of
    vegetation and woody debris on channel and
    flood-plain evolution insights from a paired
    catchment study in southeastern Australia,
    Geomorphology, 51, 7-29, 2003.
  • Shields, F.D. Jr. et al., Response of fishes and
    aquatic habitats to sand-bed stream restoration
    using large woody debris, Hydrobiologia, 494,
    251-257, 2003
  • Roni, P. and T. P. Quinn, Density and size of
    juvenile salmonids in response to placement of
    large woody debris in western Oregon and
    Washington streams, Canadian J of Fisheries and
    Aquatic Science, 58, 282-292, 2001
  • Larson, M., D. B. Booth, and S. A. Morley,
    Effectiveness of large woody debris in stream
    rehabilitation projects in urban basins,
    Ecological Engineering,18 (2001) 211226.

3
Vegetation Management in Floodplains
  • Planting native forests and protecting their
    animal communities
  • Planting to resist invasive weeds
  • Allowing other aspects of channel-floodplain
    restoration design to create diversity of
    habitats for plant colonization and population
    dynamics

4
Roles of Vegetation in Channel Restoration
  • Riparian shading
  • light and water temperature
  • Mainly for small streams
  • Provide debris (leaves, etc.) as food (algae
    invertebrates fish).
  • River Continuum Off-channel habitat, and
    Flood-Pulse concepts guide expectations about the
    situations where food-supply role should be
    important?
  • Resisting rapid bank slumping (up to some bank
    height) slow channel migration
  • Resisting gullying/washing of banks, especially
    where cattle/elk grazing has degraded channel
    banks
  • Source of Large Woody Debris to stabilize
    spawning gravel in channels that would other wise
    be too steep to store gravel
  • Source of LWD to provide variance in flow
    velocity for resting/feeding
  • Source of LWD to provide shelter from predators
    for small fish

5
Complete stabilization of banks and bars
considered undesirable
  • Some channel shifting is now valued (see earlier
    notes)
  • Both pool and shallow water habitat near banks
    favored by channel asymmetry

6
Preference is for a dynamic balance of
recruitment and succession and demise in
floodplains and riparian zones
  • Veg. colonization of banks and floodplain favored
    by fluctuating hydrograph that disseminates seeds
    and supports moist root-zone for germination and
    growth
  • Sufficiently slow channel migration to allow
    forest maturation and strong root mats
  • Toppling of riparian trees with intact root boles
    into channels
  • Scouring away of trees that colonize point bars,
    resist bed-material movement, and confine flow so
    that it scours a tabular channel
  • Age succession of substrate, species and tree age
    driven by channel migration
  • Occasional destruction of floodplain trees during
    overbank flow or channel avulsion, creating
    diversity of tree age and canopy density

7
In-channel Wood (LWD)
  • Originally removed during channel
    improvement. Still is in many projects
  • Navigation hazard
  • Damage in-channel structures such a bridges
  • Flood hazard
  • Increases flow resistance
  • Wedges against bridges and other structures
  • Flotsam
  • Jams can force channel migration or avulsion
  • Thought to block fish passage
  • Still being removed in PNW in early 1980s

8
In-channel Wood (LWD) reduced by
  • Extensive de-snagging by boats and ground
    machinery
  • To reduce flood stages
  • To lower water tables for agricultural drainage
  • To facilitate navigation
  • Snag density reduced from 550/km in 1850s to
    3/km today in Willamette R., Oregon (Sedell
    Froggat 1984)
  • Removal of source trees by riparian deforestation
    for timber and agriculture
  • Removal of tree recruitment by cattle browsing
  • Scouring away of LWD by increased flooding and
    sediment transport

9
LWD is a natural component of rivers in many
parts of the world
  • Not in deserts, tundra, and large, steep mountain
    rivers
  • No longer in agricultural or agricultural regions
    (unless riparian trees are maintained and floods
    controlled), and not for a long time (if ever) in
    intensively logged regions
  • Natural LWD loading of channels probably depends
    on
  • Channel size (drainage area) and gradient
  • Production rate of large trees, especially those
    with wood that resists decay and abrasion
  • E.g. Australian LWD loads (m3/m2 or / km)
    generally higher (low stream power, dense wood
    NZ generally lower (high stream power) than in N.
    hemisphere rivers

10
Too late! Beginning in 1980s .
  • Reduction of reach-scale flow resistance hard to
    document
  • Doesnt block fish migration Limit?
  • Provides habitat for fish and other organisms
  • Slow velocity zones
  • Pools and overhangs for refuge
  • Feeding/resting sites
  • Spawning sites on trapped gravel
  • Shade
  • Increases intra-reach habitat diversity
  • Provides substrate for bacteria, invertebrates,
    algae, etc., which convert C and nutrients to
    animal food
  • Slows sediment transport and allows sediment
    storage
  • Induces channel (habitat) complexity
  • De-snagging and riparian clear-cutting continues
    in many channels/ countries

11
Origin of LWDDepends on climate (vegetation
production) and position in a watershed
  • Bank erosion and toppling
  • Self-pruning by riparian trees
  • Landslides (from hillslopes)
  • Debris flows (from steep channels upstream)
  • Fluvial transport from upstream banks and jams
  • Exhumation of logs buried in floodplain (100s to
    1000s yrs)
  • Artificial placement as fixed jams or bank
    revetments
  • There is also loss of LWD to
  • Overbank flooding
  • Decay

12
LWD budgets
  • Need to estimate long-term input rates and tempo
    from fluvial and hillslope processes
  • Decay rates (species, climate)
  • Transport rates
  • Abrasion rates per km of transport
  • Ages of wood in debris accumulations upto 1000s
    of years
  • Dendrochronology
  • 14C in wood

13
Spatial distribution of LWD at reach scale in a
natural forested stream, S.E. Australia
A. Brookes et al., Geomorphology, 2002
14
Bed and water surface profiles in natural and
de-snagged rivers, S.E. AustraliaBrooks et
al.,2003, Geomorphology
15
Active valley jam, Queets R., WAAbbe and
Montgomery, 2003, Geomorphology.
16
Deflection jam Abbe and Montgomery, 2001,
Geomorphology
17
Bar apex jam, Queets R., WAAbbe and Montgomery,
2003, Geomorphology.
18
Meander jam, Queets R., WAAbbe and Montgomery,
2003, Geomorphology.
19
Stable and unstable debris jams Abbe and
Montgomery, Geomorphology 2003
20
Log jam, Nisqually R., WA (Collins
Montgomery Restoration Ecology, 2002)
21
Log jams in Queets and Nisqually Rivers,
WashingtonD. Montgomery, GSA Today, 2004
22
Roni and Quinn, Canad. J Fisheries Aquatic
Sci., 2001
23
Roni and Quinn, Canad. J Fisheries Aquatic
Sci., 2001
24
Roni and Quinn, Density and size of juvenile
salmonids in response to placement of large woody
debris in Western Washington streams, Canad. J
Fisheries Aquatic Sci., 2001
25
F. D. Shields et al., 2003, Response of fishes
and aquatic habitats to sand-bed stream
restoration using large woody debris,
Hydrobiologia, 494, 251-257.
To stabilize incised sand-bed streams 72
structures built on concave bank toes with 1168
trees w. root balls and crowns in 2 km long
reach. 58 with metal anchors 88,000/km
26
Shields et al. (2003)
27
Shields et al. (2003)
28
Shields et al., (2003)
29
Most manipulation of LWD has been local
  • To demonstrate the value of LWD for fish
  • For natural bank stabilization (Literature of
    T. Abbe)
  • But what is the cumulative effect?

30
Most manipulation of LWD has been local
  • To demonstrate the value of LWD for fish
  • For natural bank stabilization (Literature of
    T. Abbe)
  • But what is the cumulative effect?

31
Long-term goal?
  • Gradually move away from strategies that rely on
    site-by-site installation of LWD
  • Increasingly rely on putting the
    riparian/floodplain vegetation community into a
    state in which it will
  • supply bank reinforcement of preferred kind (i.e.
    not absolute)
  • supply stable, units of large wood at a rate that
    will balance removal
  • manage the channel and downstream conditions so
    that the resulting channel complexity/blockage is
    acceptable to boating and flood-control interests
  • Not possible everywhere.
  • Need for strategic thinking connects with
    Terrestrial Ecology, Regional Ecosystem Planning,
    and Restoration courses (Frank?)
Write a Comment
User Comments (0)
About PowerShow.com