Development of innovative sediment control approaches for severely disturbed sites using GIS, modeli

1
Development of innovative sediment control
approaches for severely disturbed sites using
GIS, modeling and field experiments
Helena Mitasova, Dept. of Marine, Earth
and Atmospheric Sciences, NCSU R. McLaughlin,
Dept. of Soil Science, NCSU http//www.skagit.mea
s.ncsu.edu/helena/
2
Sediment control for severely disturbed sites
Current systems often ineffective for large,
severely disturbed sites, sediment loads exceed
state and federal standards Alternative systems
that provide cost-effective protection in
spatially and temporally complex conditions are
needed. Combine new/improved techniques with
landscape-scale, spatially explicit modeling to
fins optimal configurations and locations for
these techniques. ADD PICTURES HERE from
Charlotte and installations
3
Improved sediment control systems
get from Rich
4
Role of modeling and GIS

• - analysis of spatial pattern of water
• and sediment flow,
• - identification sediment sources and sinks,
• - design of conservation measures
• - analysis of different scenarios,
• - visualization of results

5
Spatially distributed, process-based models
SIMWE and GeoWEPP
describe basic properties
6
Overland water flow governing equations
Shallow overland flow bivariate St. Venant
equation
steady state kinematic wave with approx.
diffusive wave effect
r(x,y) , h water depth, ie rainfall excess,
v - velocity given by Mannings eq., ? -
diffusion constant the diffusion term (dependent
on h5/3) makes the equation linear in h5/3
making it possible to solve it by path sampling
method. ADD HERE full dynamics or other models
can be used for water, couple modules to create a
model as complex or as simple as needed
H. Mitasova
7
Sediment transport governing equations
Sediment transport and net erosion/deposition
model is based on 2D generalization of a 1D
hillslope erosion model used in WEPP. Using
steady state water flow as input sediment
transport is described by continuity equation
with diffusion term
where D s ( T - qs ) is sources-sinks
term D / Dc qs / T 1
(Foster and Meyer, 1972) T Kt
?p Dc Kd (? - ?c)q
c - sediment concentration, qs - sediment flow,
T - transport capacity, Dc- detachment
capacity, s(r) - first order reaction coef. ?
diffusion constant, ? - shear stress, ?c -
critical shear stress, Kt, Kd - transport and
detachment capacity coef.
8
Numerical solution path sampling method
- robust method for complex, high resolution
elevation surfaces, spatially variable land
cover, soil properties and rainfall excess -
based on duality between particle and field
representation
source is represented by particles with
increased density in disturbed areas
particle density represents water
depth initially a noisy surface
Example from Balsam mountain development NC,
lidar-based DEM
9
Numerical solution path sampling method
- path samples (particles) represent water or
sediment evolving according to the bivariate
continuity equation, solved by operator
inversion Green's function representing
short time propagation of the particles (drift
diffusion)
initial set of particles after 20000 iterations,
close to steady state
accumulated water depth after 20000 iterations
10
Numerical solution path sampling method
11
Development of SW Centennial Campus
Combining the GIS and CAD data to create digital
models of the current and future landscapes
2001
1993
future
construction
12
Change in topography
1993
DEMs (2m res) interpolated from contours and
lidar data using the RST method in GRASS
2001
high tension/low smoothing
low tension/high smoothing
13
Storm water and sediment control
storm water detention
check dam completely filled with sediment
These control measures are included as
topographic features captured e.g. by lidar
14
Overland flow
current 49 forest
construction 24 forest
0.7m3/s
0.002m3/s
discharge m3/s
Spatial distribution of overland water discharge
for 1hr steady rainfall at 46mm/hr (2 year
design storm)
15
Net erosion/deposition
0.01-6.0kg/ms erosion968kg/s
0.001kg/ms erosion87kg/s
/m2s
erosion deposition
erosion deposition
main impact of disturbance is outside
construction site stream erosion within
protective buffer
16
Overland flow and net erosion/deposition
impact of disturbance caused by concentrated
water flow that is not sufficiently reduced by
the buffer, maximum erosion rates are within the
protective buffer
Discharge m3/s
/m2s
Erosion deposition
17
Overland flow and net erosion/deposition
total erosion kg/s
Extended, high infiltration buffers can reduce
the impact
no extended buffer
forest buffer
grass buffer
current
18
Overland flow effectiveness of checkdams
Show overflow 25 year storm dams filled to the
top
current 49 forest
Spatial distribution of overland water discharge
for 1hr steady rainfall at 65mm/hr (25 year
design storm)
discharge m3/s
19
Overland dispersal flow
modeling impact of spreaders show photo
discharge m3/s
20
GeoWEPP results
discharge m3/s
21
Net erosion and deposition
Net erosion and deposition is computed as a
divergence of sediment flow.
erosion depos.
Observed colluvial deposits
Erosion/deposition as directional
derivative (change in sediment flow along 1D
flowline)
Erosion/deposition as divergence of 2D sediment
flow
22
Optimizing conservation measures
Original LU
sediment flow
net erosion/deposition Optimized
LU
23
Conclusions
- new mapping technologies provide multitemporal,
high resolution 3D representation of
landscape - new generation of spatially
distributed, process-based models
integrated with GIS - increasing importance of
stochastic techniques Future - r.terradyn
short term terrain evolution (Thaxton 2004) -
fully dynamic wave, coupled processes -
spatially distributed overland flow and erosion
data for calibration and validation
(ground-based laser scanning) - new modules
developed by international GRAS community will
support building of tools for simulation of
complex Earth systems
H. Mitasova