| 1
Model identification |
Soil
Erosion Network - Model |
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1.1
Model name |
APEX
- Water and Wind Erosion |
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1.2
Most recent version |
APEX
4220
APEX 8190
(information updated 12/2000)
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1.3
Date of release |
August
1994 |
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| 2
Water erosion and Wind Erosion |
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| 3
Contact person |
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3.1
Name |
J
R Williams |
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3.2
Address |
USDA-ARS,
808 E Blackland Road, Temple, TX 76503 |
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3.3
Tel |
+1
817 770 6508 |
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3.4
Fax |
+1
817 770 6561 |
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3.5
Email |
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| 4
Model Author(s) |
J
Williams, J Arnold, J Kiniry, K Potter, K King |
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| 5
Model components |
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5.1
Water erosion: |
USLE/MUSLE
(several variations) |
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5.2
Wind erosion: |
Modified
Manhattan KS model (Bagnold energy component) |
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5.3
Hydrology: |
Runoff-
modified SCS CN; Peak rate-modified rational or SCS TR-55; ET:
4 options options, Penman, Penman-Montieth, Hargreaves, Priestly-Taylor |
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5.4
Site/topography: |
Whole
Farm/small watershed/landscape; watershed may be subdivided |
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5.5
Plant growth: |
General
crop growth model simulates about 30 crops |
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5.6
Management: |
Irrigation,
fertilizer, liming, furrow diking, crop rotation. Variety of
tillage operations |
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5.7
Soil: |
Up
to 30 soil layers. Core data: Bulk density, field capacity,
wilting point, organic Co texture |
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5.8
Chemistry: |
N
and P cycling; pesticide fate; water quality |
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5.9
Weather: |
Precipitation,
temperature (max, min) solar radiation, relative humidity, wind
(speed & direction). Input or generated |
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| 6
Model characteristics |
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6.1
Spatial |
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6.1.1
Class of area: |
Whole
farm, small watershed, landscape |
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6.1.2
Flow routing system: |
Streamline
- natural subareas |
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6.1.3
Minimum area: |
1
ha |
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6.1.4
Maximum area: |
100
km2 |
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6.2.
Temporal |
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6.2.1
Timestep: |
1
day |
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6.2.2
Single or multiple event? |
Continuous |
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6.2.3
Maximum simulation duration: |
1000
years |
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| 7
Model's representation of processes |
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7.1
Water erosion processes |
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7.1.1
Interrill: |
Combined |
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7.1.2
Rill: |
Combined |
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7.1.3
Gully: |
None
now - development is high priority |
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7.1.4
Streambank: |
Yes
- sediment routing degrades channel as a function of flow velocity |
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7.1.5
Deposition: |
Yes
- governed by flow velocity and particle size |
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7.2
Wind erosion processes: |
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7.2.1
Creep/surface roll: |
Yes
- Bagnolds eg |
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7.2.2
Saltation: |
Yes
- Bagnolds eg |
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7.2.3
Suspension; |
Yes
- Bagnolds eg |
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7.3
Hydrological processes: |
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7.3.1
Evaporation/transpiration |
Penman,
Penman - Montieth, Hargreaves, Priestly- Taylor |
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7.3.2
Runoff: |
SCS
CN modified for volume; modified rational of SCS TR55 for peak
rate |
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7.3.3
Infiltration: SCS CN modified |
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7.3.4
Subsurface flow: |
Yes
- lateral and vertical computed simultaneously when field capacity
is exceeded. Vertical governed by saturated conductivity; lateral
by land slope |
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7.3.5
Return flow: |
Yes
- function of lateral flow and subsurface travel time from watershed
centroid to outlet |
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7.4
Plant processes: |
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7.4.1
Light interception and photosynthesis: |
Yes
- Beer's law; potential daily biomass growth limited by minimum
stress factor - water, nutrients, temperature, aeration |
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7.4.2
Dry matter and residue: |
Yes
- at harvest yield is removed (harvest index). Standing dead
residue falls to the soil surface at a rate driven by accumulated
rainfall, and surface & subsurface residue is decayed as
a function of soil moisture and temperature. |
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7.4.3
Root growth: |
Depth
driven by heat units; limited to max for crop or soil depth.
Root mass a function of water use. Limited by bulk density,
alumini saturation, or temperature |
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7.4.4
Pests: |
Insects,
weeds, diseases. Generic model driven by moisture, temperature
& biomass |
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7.4.5
CO2 sensitivity: |
Through
canopy resistance in Penman-Montieth eqn and crop coefficient
converting energy to biomass |
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7.5
Soil: |
Up
to 30 layers permitted with variable thickness. Erosion removes
soil from profile; layer 2 becomes thinner until it approaches
O, then removed from system. Properties change with erosion,
tillage mixing, mineralization of organic matter |
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7.5.1
Crust development: - |
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7.5.2
Aggregate properties: |
Large
and small aggregates estimated from texture - and used in sediment
routing |
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7.6
Chemistry: |
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7.6.1
Nutrients: |
N
and P cycles: mineral, organic (NO3, NH3,
active & stable organic N; labile P, active and stable mineral
and organic P. Water and sediment transport, crop uptake, mineralization-
immobilization nitrification, denitrification, N fixation, volatilization |
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7.6.2
Carbon: |
Tracks
organic N |
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7.6.3
Pesticides: |
GLEAMS
pesticide component. Wash off of plants, decay in soil &
on foliage, leaching runoff and sediment transport |
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7.6.4
Other contaminants: |
None |
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7.7
Weather: |
Precipitation,
temperature (max & min), solar radiation, wind speed, relative
humidity. Input or generated |
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| 8
Input Data (* = Mandatory) |
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8.1
Weather: |
Precipitation*,
temperature* (monthly means), solar radiation, wind speed, relative
humidity |
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8.2
Soil: |
Bulk
density*, texture*, Organic C*, field capacity, wilting point,
saturated conductivity, % rock, pH, sum of bases, CEC, Al
saturation, CaCO3, labile P, mineral P
active & stable, NO3, Organic N active &
stable. |
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8.3
Hydrology: |
SCS
CN2, watershed area, channel length & steepness,
Mannings N. Optional: channel depth |
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8.4
Plant cover: |
Crop
parameter table; planting and harvest dates |
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8.5
Soil surface cover: |
Initial
standing and flat residue |
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8.6
Management: |
Tillage
table; operation schedule (complete crop rotation by dates) |
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8.7
Topography/site characteristics: |
Land
slope & steepness, Mannings N |
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8.8
Micro-topography: |
Random
roughness and ridge interval and height created by each tillage
operation |
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| 9
Output data |
Weather,
hydrology, erosion, nutrients, pesticides, crop production,
soil properties. By sub-area, routing reach and total watershed.
Option S: daily, monthly, annual; user selects outputs |
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| 10
Programming language |
Fortran |
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| 11
Computer requirements |
IBM
PC compatible with at least 640K |
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| 12
Documentation |
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12.1
Scientific documentation: |
Sharpley
& Williams, 1990. EPIC-Erosion/Productivity Impact Calculator:
1. Model Documentation, USDA Tech Bull # 1768. |
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12.2
User's guide: |
EPIC
User's Guide; USDA ARS SCS, and TAES; Vanicek and Daneshil Editors. |
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12.3
Technical documentation: |
Sharpley
& Williams, 1990. EPIC-Erosion/Productivity Impact Calculator:
2. User Manual. |
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| 13
Availability |
Upon
request from developer |
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