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?)