1. Forest Roads
Colleen O. Doten
August 18, 2004

2. Outline
Forest Roads in the Distributed hydrology-soil-vegetation model
Erosion and Sediment Transport Module
Implementation
Output

3. Forest Roads in DHSVM Interception of shallow groundwater
Flows through the road-side ditch network
Discharges from culvert

4. Hydrologic Impacts of Forest Roads
Result of a number of characteristics
Location in hillslope and upslope contributing area (user specified)
Depth of road-side ditches (user specified)
Road drainage connectivity (DEM resolution)
Culvert density (user specified)
Soil properties (i.e., depth, hydraulic conductivity) (user specified)

5. Hydrologic Impacts of Forest Roads
Bowling and Lettenmaier(1997) and LaMarche and Lettenmaier (1998)
Deschutes River subbasins: road densities from 3.2 to 5.0 km/km2
Increase in peak flows
Average change in peaks over threshold: 1.8 to 9%

6. Hydrologic Impact of Forest Roads
Drier with roads
Wetter with roads
Hard and Ware Creeks, WA

7. Outline Distributed hydrology-soil-vegetation model
Erosion and Sediment Transport Module
Implementation
Output

8. Erosion and Sediment Transport Module
MASS WASTING
Soil Moisture Content Q
Qsed
Sediment
Channel Flow
Sediment
DHSVM
Precipitation
Leaf Drip
Infiltration and Saturation Excess Runoff
CHANNEL ROUTING
Erosion
Deposition
HILLSLOPE EROSION
ROAD
EROSION

9. Over road Flow
Runoff generation by infiltration excess is determined by DHSVM.
Runoff is partitioned based on area of the road in the grid cell.
Flow is modeled using an explicit finite difference solution of the kinematic wave approximation to the Saint-Venant equations.

10. Over road Flow Routing
Flow enters the road-side ditch in the grid cell in which it was generated (Wigmosta and Perkins, 2001)
Routing takes into account crown
hillslope
road crown
road- side ditch
fillslope

11. Mechanisms of Soil Particle Detachment
Sediment becomes available for transport by:
two mechanisms (roads)
Effects of maintenance and use
erodibility coefficients
particle size
raindrop
impact
shearing by overland flow
Mechanisms of Soil Particle Detachment

12. Soil particle detachment by raindrop impact
Dr = cfkr2
where:
cf erodibility coefficient
k reduction factor due to surface water depth
r rainfall intensity
KINEROS

13. Soil detachment by runoff
Modeled with transport capacity (TC) as a balance between erosion and deposition.
where:
cg = CHvs/h
CH a flow detachment efficiency coefficient
vs particle settling velocity
C sediment concentration
A flow area
h flow depth
KINEROS

14. Sediment Transport
Sediment available for transport is routed using a four-point finite difference solution of the two-dimensional conservation of mass.
Amount transported is limited by the transport capacity.

15. Four-point finite difference equation
Current time step, current pixel concentration
Previous time step, current pixel mass
Detachment
(rain and overland flow)
Previous time step, upstream pixel mass
Current time step, upstream pixel mass
Current time step, current pixel flow rate

16. Transport capacity relationship
KINEROS (Woolhiser) relationship
Same as Hillslope erosion, except:
is m/s

17. Sediment Routing Road surface sediment:
Routed according to the crown type.
Added to the road-sided ditch is routed through the network to a culvert.
Delivery from culvert to stream based on:
proximity
particle size (Duncan et al., 1987):
Particle Size, mm
Percent Delivered
0.5-2 10 30
≤0.63
100

18. Outline Distributed hydrology-soil-vegetation model
Erosion and Sediment Transport Module
Implementation
Output

19. Test Catchment – Rainy Creek
Existing road network
Total Length: 46 km
Density: 1.05 km/km2
Road Surface Area: 0.23 km2
No. Culverts: 284
Culvert locations:
stream crossings (91)
road low points (193)
Road Segments: 332

20. Road Classes Class ID Description Road Width, m Crown Type
Ditch Width, m
Ditch Depth, m
106
Road, Unimproved, Class 4
4.267
Outsloped
0.914
0.305
515
Road, Light-Duty, Dirt, Class 3C
4.572
Insloped
518
Road, Light-Duty, Gravel, Class 3B
5.486
Crowned
1.219

21. Road Statistics Class ID Total Length, m % of Total Length
Total Area, m2
% of Total Area
106
4,797
10.4
20,469
8.9
515
18,516
40.0
84,651
36.9
518
22,978
49.6
126,057
54.5

22. Sediment Module Implementation
Spatially constant parameters
road crown: 0.02 meters/meter (Road Preconstruction Handbook)
Spatially variable parameters
Manning’s roughness coefficient, n: – 0.02 (KINEROS2 model documentation)
Rainsplash erodibility coefficient: 200 – 300 (Smith et al. 1999)
Overland flow erodibility coefficient: – (Smith et al. 1999)
d50: 0.1 – 10 mm (Dietrich et al., 1982)
Run for a six-year period: 10/1/1991 to 9/30/1997

23. Outline Distributed hydrology-soil-vegetation model
Erosion and Sediment Transport Module
Implementation
Output

24. Default Output AggregatedSediment.Values MassSediment.Balance
Road erosion (basin average in m)
Road erosion delivered to hillslope (basin average in m)
Total overroad inflow (kg)
MassSediment.Balance
Total culvert return sediment flow (kg) 
Total culvert sediment to channel (kg)
Total amount of sediment stored in channels (kg)
Final Sediment Mass Balance
Basin Average Road Surface Erosion
Road Surface Erosion (mm): -7.51e-03
Road Surface Erosion (kg/hectare): -2.02e+02
Road Sediment to Hillslope (mm): 2.12e-03
Average Road Surface Erosion
Road Surface Erosion (mm): -1.43e+00
Road Surface Erosion (kg/hectare): -3.83e+04
Road Sediment to Hillslope (mm): 4.02e-01

25. Default/Optional Output
Sed.Road.Flow
total mass (kg) in the segment
total outflow concentration (ppm) from the segment
Sed.Road.FlowOnly: total outflow concentration (ppm) from the segment
Model Map (binary file) and Graphic Image (real-time):
Road Surface Erosion
Sum of lateral inflows (hillslope and road surface) (ascii file)

26. Model Results Simulated Rates, kg/ha/yr Published Rates, kg/ha/yr
Road surface erosion: 17 – 41 (164 – 394 kg/km road) (3,247–7,842 kg/ha of road)
Range based on minimum (0.0025) and maximum (0.035) overland flow erodibility coefficient
Changes in raindrop erodibility coefficient (100 – 2 x 107) had no affect
Published Rates, kg/ha/yr
Road surface erosion:
3,800 to 500,000 kg/km of road Olympic Peninsula, WA (Reid and Dunne, 1984)
12,000 to 55,000 kg/ha of road central ID (Ketcheson et al., 1999)

27. Sensitivity Analysis
Road erosion increases with decreasing particle size (d50 = 10 mm vs 0.1 mm)
Road erosion increases with increasing overland flow erodibility coefficient (CH = vs )
Road erosion increased with decreasing stream power criteria
Variables with little or no effect:
Cell factor
Manning’s n
Particle density

28. References
Dietrich, R.V., J.J.T. Dutro, and R.M. Foose, 1982: AGI Data Sheets for geology in the field, laboratory, and office, 2nd ed., American Geological Institute, Falls Church, VA.
Duncan, S.H., R.F. Bilby, J.W. Ward and J.T. Heffner, 1987: Transport of Road-Surface Sediment Through Ephemeral Stream Channels, Wat. Resour. Bull., 23,
Ketcheson, G.L., W.F. Megahan, and J.G. King, 1999: "R1-R4" and "BOISED" Sediment Production Model Tests using Forest Roads in Granitics, J. Amer. Water Resour. Assoc., 35,
KINEROS2 model documentation (
Smith, R.E., D.C. Goodrich and C.L. Unkrich, 1999: Simulation of selected events on the Catsop catchment by KINEROS2, A report for the GCTE conference on catchment scale erosion models, Catena, 37,
Reid, L.M., and T. Dunne, 1984: Sediment production from forest road surfaces, Water Resour. Res., 29,
Wigmosta, M.S. and W.A. Perkins, 2001: Simulating the effects of forest roads on watershed hydrology, In: Land Use and Watersheds: Human Influence on Hydrology and Geomorphology in Urban and Forest Areas, M.S. Wigmosta and S.J. Burgess (eds), AGU Water Science and Application, V.2, p
Woolhiser, D.A., R.E. Smith and D.C. Goodrich, 1990: KINEROS, A kinematic runoff and erosion model: documentation and user manual, USDA-Agricultural Research Service, ARS-77, 130 pp.
Ziegler, A.D., T.W. Giambelluca, and R.A. Sutherland, 2001: Erosion prediction on unpaved mountain roads in northern Thailand: validation of dynamic erodibility modeling using KINEROS2, Hydrol. Process., 15,

29. Culvert Discharges