Title: Vegetation Management in River Restoration
1Vegetation Management in River Restoration
- Floodplains
- Riparian zones
- Channels
2Readings 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.
3Vegetation 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
4Roles 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
5Complete 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
6Preference 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
7In-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
8In-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
9LWD 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
10Too 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
11Origin 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
12LWD 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
13Spatial distribution of LWD at reach scale in a
natural forested stream, S.E. Australia
A. Brookes et al., Geomorphology, 2002
14Bed and water surface profiles in natural and
de-snagged rivers, S.E. AustraliaBrooks et
al.,2003, Geomorphology
15Active valley jam, Queets R., WAAbbe and
Montgomery, 2003, Geomorphology.
16Deflection jam Abbe and Montgomery, 2001,
Geomorphology
17Bar apex jam, Queets R., WAAbbe and Montgomery,
2003, Geomorphology.
18Meander jam, Queets R., WAAbbe and Montgomery,
2003, Geomorphology.
19Stable and unstable debris jams Abbe and
Montgomery, Geomorphology 2003
20Log jam, Nisqually R., WA (Collins
Montgomery Restoration Ecology, 2002)
21Log jams in Queets and Nisqually Rivers,
WashingtonD. Montgomery, GSA Today, 2004
22Roni and Quinn, Canad. J Fisheries Aquatic
Sci., 2001
23Roni and Quinn, Canad. J Fisheries Aquatic
Sci., 2001
24Roni 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
25F. 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
26Shields et al. (2003)
27Shields et al. (2003)
28Shields et al., (2003)
29Most 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?
30Most 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?
31Long-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?)