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

HILLSLOPE EROSION

Soil Moisture Content

CHANNEL ROUTINGPrecipitationLeaf Drip

Infiltration and Saturation Excess Runoff

DHSVM

Q

Qsed

Sediment

MASS WASTING

Erosion

Deposition

ROADEROSION

Sediment

Channel Flow

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

road crown

road- side ditch

hillslope

fillslope

Detachment

• Sediment becomes available for transport by:– two mechanisms

(roads)

• Effects of maintenance and use– erodibility coefficients– particle sizeshearing by overland flow

raindropimpact

Mechanisms of Soil Particle Detachment

Soil particle detachment by raindrop impact

Dr = cfkr2

where:cf erodibility coefficient k reduction factor due to surface water depthr 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 velocityC sediment concentrationA flow areah flow depth

ACTCcDF g )(

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.

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Four-point finite difference equation

Detachment (rain and overland flow)

Current time step, current pixel concentration

Current time step, upstream pixel mass

Current time step, current pixel flow rate

Previous time step, current pixel mass

Previous time step, upstream pixel mass

Transport capacity relationship

• KINEROS (Woolhiser) relationship

• Same as Hillslope erosion, except:is 0.0004 m/s

)()1(

05.02 cg

Sh

dTC

c

Sediment RoutingRoad 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

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 0.914 0.305

518 Road, Light-Duty, Gravel, Class 3B

5.486 Crowned 1.219 0.305

Road Classes

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

Road Statistics

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

– Road erosion (basin average in m) – Road erosion delivered to hillslope (basin average in m) – Total overroad inflow (kg)

• MassSediment.Balance– Road erosion (basin average in m) – Road erosion delivered to hillslope (basin average in m) – Total overroad inflow (kg) – 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+02Road 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+04Road 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 ResultsSimulated Rates, kg/ha/yrRoad 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/yrRoad surface erosion:

– 3,800 to 500,000 kg/km of roadOlympic 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

ReferencesDietrich, 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