DHSVM Hillslope Erosion Modeling Theory - PowerPoint PPT Presentation

1 / 22
About This Presentation
Title:

DHSVM Hillslope Erosion Modeling Theory

Description:

Fox. Comments. 1970. 1969. 1968. 1967. Watershed. Erosion ... There is no silver bullet. Three main types of transport capacity equations: Unit stream power; ... – PowerPoint PPT presentation

Number of Views:315
Avg rating:3.0/5.0
Slides: 23
Provided by: jlan6
Category:

less

Transcript and Presenter's Notes

Title: DHSVM Hillslope Erosion Modeling Theory


1
DHSVM Hillslope Erosion Modeling Theory
  • Presented by
  • Jordan Lanini
  • USDA FS DHSVM Sediment Module Demonstration
  • August 18, 2004

Photo courtesy of USDA Natural Resources
Conservation Service
2
Presentation outline
  • Theoretical composition
  • Data requirements
  • Questions

3
Theoretical Background
  • Hillslope erosion consists of three components
  • Detachment
  • Transport
  • Deposition
  • Requires kinematic runoff routing to calculate
    erosion and transport

raindrop impact
leaf drip impact
shearing by overland flow
Mechanisms of Soil Particle Detachment
L. Bowling, J. Lanini, N. Voisin
4
Current DHSVM Runoff Generation and Routing
  • Runoff is produced via
  • Saturation excess (pixels 6 and 7)
  • Infiltration excess based on a user-specified
    static maximum infiltration capacity (pixel 3)
  • Runoff is routed to the downslope neighbors one
    pixel/time step

5
Runoff Generation Dynamic Infiltration Excess
  • Calculation of maximum infiltration capacity
  • The first timestep there is surface water on the
    pixel, all surface water infiltrates.
  • If there is surface water in the next timestep,
    the maximum infiltration capacity is calculated
    based on the amount previously infiltrated.
  • Dominant form of runoff generation on unpaved
    roads and post burn land surfaces

N. Voisin
6
Kinematic Runoff Routing
  • Pixel to pixel overland flow routed using an
    explicit finite difference solution of the
    kinematic wave approximation to the Saint-Venant
    equations
  • Mannings equation is used to solve for flow area
    in terms of discharge
  • Per DHSVM timestep, a new solution sub-timestep
    is calculated satisfying the Courant condition,
    which is necessary for solution stability.

L. Bowling
7
Soil particle detachmentRaindrop and leaf drip
impact
  • Where
  • is soil detached by raindrop impact in kg m-2
    s-1,
  • is a raindrop soil erodibility coefficient
    (J-1),
  • is the portion of ground covered by
    understory,
  • is the portion of canopy cover for each grid
    cell,
  • is the square of raindrop momentum, and
  • is the square of leaf drip momentum.

Wicks Bathurst, 1996 Photo courtesy of USDA
Natural Resources Conservation Service
8
Water depth correction
  • Standing water diminishes the effects of drop
    impact

Wicks Bathurst, 1996
9
Soil detachment by runoff
  • Modeled with transport capacity (TC) as a balance
    between erosion and deposition.
  • Where
  • is a flow detachment efficiency coefficient.
    This reduces erosion for cohesive soils
  • is the flow width
  • is particle settling velocity
  • is sediment concentration.

Morgan et al, 1998
10
Soil detachment by runoff (cont.)
  • Flow detachment efficiency
  • during deposition
  • for cohesive soils during detachment
  • From Wicks Bathurst but detachment decreases
    too quickly with increased cohesion.
  • Therefore, different relationships between
    cohesion and detachment were examined.

11
Soil detachment by runoff (cont.)
12
Surface erosion rates in the Eastern Cascades
  • Helvey (1980) compiled pre- and post-fire erosion
    rates from three experimental watersheds within
    the Entiat basin

13
Soil detachment by runoff (cont.)
  • Rainy Creek scenario analysis
  • Relationship was adjusted to observed Cascade
    erosion rates
  • Selected relationship
  • Rainy Creek has higher precipitation than Entiat
  • Model numbers are total erosion and not delivered
    sediment

14
Transport Capacity
  • Numerous equations exist for transport in
    overland flow, but
  • There is no silver bullet.
  • Three main types of transport capacity equations
  • Unit stream power
  • Mean stream power
  • Shear stress.

Prosser Rustomji, 2000 Photo courtesy of USDA
Natural Resources Conservation Service
15
Transport capacity (cont)
  • How to decide?
  • Govers (1992) compiled data from transport
    capacity studies and evaluated several equations
    for overland flow application.
  • Govers found that no existing equation worked
    well over a wide range of particle sizes and
    slopes.
  • Govers saw good results from a unit stream power
    equation with a threshold and a correction for
    particle diameter.

16
Selected transport capacity relationship
  • Kineros (Woolhiser) relationship
  • Contains unit stream power threshold and particle
    diameter adjustment
  • is the density of water
  • d is the particle diameter
  • S is the slope
  • H is the flow depth
  • is a critical unit stream power value (0.004
    m/s)

17
Limitations on transport capacity
  • Govers (1992) found maximum transport capacities
    of 0.35 m3/ m3 during flume experiments
  • Model limits transport calculations to flow
    depths greater than 1 mm (Woolhiser relationship
    results in excessive TC below this threshold)

18
Hillslope Sediment Routing
  • Sediment is routed using a four-point finite
    difference solution of the two-dimensional
    conservation of mass equation.
  • If the pixel contains achannel (including road
    side ditches), all sediment and water enters
    the channelsegment.

sediment and water
L. Bowling
19
Four-point finite difference equation
Detachment (rain and overland flow)
Current time step, current pixel concentration
Previous time step, current pixel mass
Previous time step, upstream pixel mass
Current time step, upstream pixel mass
Current time step, current pixel flow rate
Where ? is a weighting factor, a is
(n/(s0)0.5)3/2 and ß is 3/5.
20
Data Input Needed for Hillslope Erosion Model
  • Soils
  • Bulk Density
  • Manning n
  • K index
  • d50
  • cohesion distributions (mean, stand deviation,
    minimum value, maximum value)

21
Questions?
Photo by Dennis Lettenmaier
22
References
  • Bagnold, R.A., 1966, An approach of sediment
    transport model from general physics. US Geol.
    Survey Prof. Paper 422-J.
  • Epema G.F., H. Th. Riezebos 1983 Fall Velocity
    of waterdrops at different heights as a factor
    influencing erosivity of simulated rain. Rainfall
    simulation, Runoff and Soil Erosion. Catena
    suppl. 4, Braunschweig. Jan de Ploey (Ed).
  • Everaert, W., 1991, Empirical relations for the
    sediment transport capacity of interill flow,
    Earth Surface Processes and Landforms, 16,
    513-532.
  • Govers, G., 1992 Evaluation of transporting
    capacity formulae for overland flow, In Overland
    Flow Hydraulics and Erosion Mechanics, Parsons
    J.A. and Abrahams A.D. Eds. UCL Press Limited,
    London.
  • Helvey, J.D. 1980, Effects of a North Central
    Washington wildfire on runoff and sediment
    production, Water Resources Bulletin, 16(4)
    627-634.
  • Morgan, R.P.C., J.N. Qinton, R.E. Smith, G.
    Govers, J.W.A. Poesen, K. Auerswald, G. Chisci,
    D. Torri and M.E. Styczen, 1998, The European
    soil erosion model (EUROSEM) a dynamic approach
    for predicting sediment transport from fields and
    small catchments, Earth Surface Processes and
    Landforms, 23, 527-544.
  • Prosser, I.P. and P. Rustomji 2000 Sediment
    transport capcity relations for overland flow,
    Progress in Physical Geography 24(2), 179-193.
  • Smith R.E. and J.Y. Parlange 1978 A
    parameter-efficient hydrologic infiltration
    model. Wat. Resour. Res. 14(3), 533-538.
  • Smith R.E., D.C. Goodrich, D.A. Woolhiser, and
    C.L. Unkrich 1995 KINEROS a kinematic runoff
    and erosion model. Chapter 20 in Computer Models
    of Watershed Hydrology, Water Resources
    Publication, Highland Ranch, Colorado. p697-732.
  • Wicks, J.M. and J.C. Bathurst, 1996, SHESED a
    physically based, distributed erosion and
    sediment yield component for the SHE hydrological
    modeling system, Journal of Hydrology, 175,
    213-238.
  • 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.
Write a Comment
User Comments (0)
About PowerShow.com