evaluation of the effects of hydrologic and geomorphic ... · • this approach necessitates...
TRANSCRIPT
Evaluation of the Effects of Hydrologic and Geomorphic Processes and Bottomland
Hardwood Plant Communities of the Lower White River Basin: An integrated approach
Sammy L. King1, Richard Keim2, and Cliff R. Hupp3
1Louisiana Cooperative Fish and Wildlife Research Unit, USGS, 124School of Renewable Natural Resources, LSU
2School of Renewable Natural Resources, LSU Agricultural Center
3USGS, 430 National Center, Reston, VA
Impacts to White River
• Base‐level lowering of the Mississippi River (Biedenharn and Watson 1997)
• Hydroelectric dams
• Navigational lock at its confluence with the Mississippi River
• Navigation channel along much of its course
• Irrigation pump that diverts surface water from the river
Rivers as Process‐Response Systems• Rivers are process‐response systems that fluctuate around an “endpoint” of dynamic equilibrium
• Changes in sediment load, channel depth, and discharge, among other parameters, can result in rapid changes in the river and associated floodplain
Geomorphic Impacts of Dams
Incised Channel Lower Floodplain
Headcutting
Photos courtesy of USFWS
Impacts of Channel Entrenchment
Table
Water
Table
Water
Objectives1) Conduct a rapid assessment of bank stability/failure at selected points
from the mouth of the river to Newport2) Determine annual (or more frequent) bank erosion and sedimentation
rates along selected reaches of the floodplain3) Expand the validation of the COE HEC‐GeoRAS model to include the
floodplain as well as the channel4) Determine the effects of river stage (and the potential effects of
entrenchment) on groundwater dynamics in different geomorphic settings
5) Develop a process‐based model that will allow us to predict groundwater dynamics at specific locations within the floodplain based on reach‐ and site‐specific characteristics, including local watershed inputs, geomorphic surfaces, soils, and riverine connectivity
6) Determine growth rates and stand establishment of bottomland hardwoods within selected plant communities /geomorphic surfaces
7) Develop an integrated, spatially‐explicit, multi‐scale simulation model to determine the effects of current and potential hydrologic processes on the distribution of bottomland hardwood plant communities on the floodplain of the White River
Geomorphic Study
0
50000
100000
150000
200000
250000
300000
1/1/
1912
1/1/
1916
1/1/
1920
1/1/
1924
1/1/
1928
1/1/
1932
1/1/
1936
1/1/
1940
1/1/
1944
1/1/
1948
1/1/
1952
1/1/
1956
1/1/
1960
1/1/
1964
1/1/
1968
1/1/
1972
1/1/
1976
1/1/
1980
1/1/
1984
1/1/
1988
1/1/
1992
1/1/
1996
Time
Flow
(CFS
)
Pre‐ and post‐dam flow on the lower Roanoke R.
1950Dam closure
Transect 9
0 200 400 600 800 1000
Elev
atio
n (m
)
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
Sedi
men
t dep
ositi
on ra
te (m
m/y
r)
0
1
2
3
4
5
Elevation (m)Deposition rate (mm/yr)
Transect 23
Distance from bank (m)0 500 1000 1500 2000
Elev
atio
n (m
)-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
Sedi
men
t dep
ositi
on ra
te (m
m/y
r)
1
2
3
4
5
6
7
8
Distance from bank (m)
IMPACT
FLOW REGULATION
(Hupp et al. 2009)
Bank Erosion and Floodplain Sedimentation, Volume
(Hupp et al.
River km
25-3233-39
41-4749-55
56-6364-70
72-7880-86
88-9596-102
104-110111-119
120-126129-134
137-143144-150
152-157159-165
166-173
Mas
s w
astin
g in
dex
-4
-2
0
2
4
6
8
Sec
chi d
epth
(m)
0.0
0.5
1.0
1.5
2.0
2.5
Essentially all suspendedmaterial in the lower riverIs derived from bankerosion
particle‐by particle erosion
Mass wasting
Erosion pins
Bank failure has yet to be captured in pin analyses
blue=secchi depthred=mass wasting index
(Hupp et al. 2009)
Mostly fluvial (particle) erosionLarge primary mass wasting, probably a rotational slump, withdeep bank instability.
Arcuate failure, primary
Slab failure, secondary
Impacts of Low Flows on Potential of Bank Failure
Should be exceedance value of about 20%
MeasuringFloodplain Deposition
Geomorphic Study
• Overall objectives are to determine the geomorphic condition of the river, particular as it relates to current (and future) flow regimes (including the effects of sustained low flows on bank erosion and downstream sedimentation)
Hydrologic Issues
• Unknown accuracy and precision of the COE HEC‐GeoRAS model – Have always suggested 1‐2 ft, but we have no idea if this is correct
– If incorrect, does it occur in a predictable manner?
– Improving our understanding of surface and subsurface groundwater dynamics is critical to model vegetation dynamics
Hydrologic Issues
• We know that there is some channel entrenchment, but what are the effects of channel entrenchment on groundwater dynamics? Has it lowered groundwater levels below the root zone?
• If so, what is the effect of various river stages on groundwater levels?
• How do groundwater (and surface water) dynamics vary within and among geomorphic features?
• If we ignore these differences (such as we currently do) will it significantly affect predictions of forest successional change?
Hydrologic Issues
• Process‐based models using soils, geomorphic surface, surface and subsurface riverine connectivity, and local watershed inputs/outputs among other measurable attributes may allow us to extrapolate to similar settings throughout the watershed
Topographic features within the floodplain define surface flow boundaries
A few channelized connections allow surface exchange below flood stages
Hydrologic Model Based on Geomorphic Boundaries
General Conceptual ModelΔStorage = Rain – Evaporation ± Surface Flows ± Subsurface Exchange
RainfallEvaporation
Subsurface Exchange
Surface Flows
Rainfall: local gauges, radar estimates
Evaporation: model based on current field research in Louisiana
Subsurface Exchange: model based on recent research in Louisiana and groundwater data
Surface Flows: model based on HEC‐GeoRAS and measurements of connections
Tree Growth / Stand Development
Tree Growth / Stand Development
• Will be closely linked to hydrology and geomorphology studies; water wells/pressure transducers will be co‐located
• Sampling plots will be stratified across geomorphic features and longitudinal distance from the dam/mouth
• A combination of transects and plots will be used to insure adequate coverage of common vegetation communities
Modeling Study• Ultimately, want to develop a predictive, spatially explicit simulation model of floodplain forest dynamics that will allow for evaluation of the effects of various flow regimes
• This approach necessitates process‐based geomorphic and hydrologic models linked to tree growth and establishment
• In the original proposal, the modelling student (that integrates all components) would begin in year 2. However, funding is currently questionable for this student / study component
Near Future Milestones• In the next 30 days, we will begin efforts to identify and compile relevant datasets for this project
• In the next 60 days, we will initiate selection of study sites. We hope to complete selection of most sites during this timeframe
• The Ph.D. student will attend training for rapid geomorphic assessment
• Provided water levels are appropriate, the rapid assessment and bank erosion study will be initiated
• In the next 90 days, we hope to begin deploying pressure transducers and begin collecting vegetation data
• Very little point bar formation; it is not in equilibrium
• Go to photos of Little Red to see a bank in equilibrium
• Fig 6 is not a bank; midbanks flooded 50% of time; should be flooded 20% of time. This is showing impact of high sustained low flows.
• Measure toe slope by tying pins in laterally and vertically. Tie off boat to one of pins above water; have boat pulled into river so that nose is near edge of bank. Walk from bow of boat to stern and measure at intervals and drop measuring rod at specified distances and measure water depth.
• Cliff and them put in pins; at 1 m or break in slope. Then go back and measure how much of pin has been exposed. If pin completely gone because of mass wasting. You would put a benchmark in tree at some distance from bank; this will allow you to get measurements if entire bank erodes.
• Having done the work on Roanoke will make things a lot easier on White River
Channelization/ Channel Shortening
Nickpoint migrates upstream causing bed lowering upstream of nickpointCan reduce flood frequency and lower floodplain water table
Nickpoint (t2)
Nickpoint (t1)
New channel slope / elevation