Forest Roads Colleen O. Doten August 18, 2004

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

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

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)

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%

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

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

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

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.

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

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

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

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

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.

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

Transport capacity relationship KINEROS (Woolhiser) relationship Same as Hillslope erosion, except: is 0.0004 m/s

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 0.63-0.5 30 ≤0.63 100

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

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

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

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

Sediment Module Implementation Spatially constant parameters road crown: 0.02 meters/meter (Road Preconstruction Handbook) Spatially variable parameters Manning’s roughness coefficient, n: 0.015 – 0.02 (KINEROS2 model documentation) Rainsplash erodibility coefficient: 200 – 300 (Smith et al. 1999) Overland flow erodibility coefficient: 0.0025 – 0.35 (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

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

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

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)

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)

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 = 0.0025 vs. 0.035) Road erosion increased with decreasing stream power criteria Variables with little or no effect: Cell factor Manning’s n Particle density

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, 113-119. 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, 83-98. KINEROS2 model documentation (http://www.tucson.ars.ag.gov/kineros/Docs/DocNav.html#) 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, 457-475. Reid, L.M., and T. Dunne, 1984: Sediment production from forest road surfaces, Water Resour. Res., 29, 1753-1761. 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. 127-143. 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, 337-358.

Culvert Discharges