�� GRASS GIS - Simulation Models

Current Topics: erosion modelling, hydrological modelling, floodplain analysis, wildfire spread

Erosion modelling: ANSWERS - r.answers

The acronym for Areal Non-point Source Watershed Environmental Response Simulation model. This event-oriented, distributed parameter model is designed for erosion, sediment and water quality control planning on complex, agricultural watersheds.
It should normally be distributed in your GRASS-package. Note: ANSWERS is written in C and FORTRAN, and will require a C compiler and a FORTRAN compiler such as f77.
ANSWERS page at Purdue
GRASS man page r.answers

Erosion modelling: AGNPS 5.0

AGricultural Non-Point Source (AGNPS) is a distributed parameter model developed by Agricultural Research Service (ARS) scientists and engineers. It predicts soil erosion and nutrient transport/loadings from agricultural watersheds for real or hypothetical storms i.e., it's an event-based model. Erosion modeling is built upon the USLE applied on a storm basis; thus, it uses the EI-index for single storm events. Its hydrology is based on the Soil Conservation Service Curve Number technique. AGNPS uses another ARS developed model named CREAMS to predict nutrient/pesticide and soil particle size generation and interaction. Here is a AGNPS Page. Some help about using AGNPS can be found here. Note: AGNPS 5.0 is written in C.
References:
- GRASS man pages: r.agnps50.input, r.agnps50.run, r.agnps50.view
- Bragadin, G.L., Franchini, M., Morgagni, A., Todini, E. (1993): Agricultural non-point source nutrient loadings estimated by means of an extended version of AGNPS. The Bidente-Ronco case study - Part I. INGEGNERIA AMBIIENTALE, Vol.22, Nr.9, S. 455
- Mitchell, J.K., Engel, B.A., Srinivasan,R., Wang, S.S.Y. (1993): Validation of AGNPS for Small Watersheds Using an Integrated AGNPS/GIS System. WATER RESOURCES BULLETIN- AMERICAN WATER RESOURCES ASSOCIATION, Vol.29, Nr.5, S. 833
- Robert Alton Young, C.A. Onstad, D.D. Bosch, W.P. Anderson. (1989) AGNPS: A nonpoint-source pollution model for evaluating agricultural watersheds. Jour. of Soil and Water Conservation. v44, n2. ISSN 0022-4561
- Srinivasan, R. and B.A. Engel, (1991), A Knowledge Based Approach to Extract Input Data From Gis, ASAE Paper No. 91-7045, American Society of Agricultural Engineers, St. Joseph, Michigan.
- Srinivasan, R. and B.A. Engel, (1991), GIS: A Tool For Visualization and Analyzation, ASAE Paper No. 91-7574, ASAE, St. Joseph, Michigan.
- Srinivasan, R., Engel, B.A., Wright, J.R., Lee, J.G.(1994): The Impact of GIS-derived Topographic Attributes on the Simulation of Erosion Using AGNPS. APPLIED ENGINEERING IN AGRICULTURE , Vol.10, Nr.4, S. 561

Erosion modelling: KINEROS - r.kineros

KINEROS represents a watershed as a set of related elements. Elements may be hillslopes, channels or ponds. A computational order must be specified so that boundary conditions for an element, such as the amount of water contributed by lateral hillslopes and upstream tributaries, are available.
(Smith et al., in press; Woolhiser et al., 1990).
GRASS man page r.kineros

Rainfall-runoff modelling: TOPMODEL - r.topmodel

TOPMODEL is a rainfall-runoff model that bases its distributed predictions on an analysis of catchment topography. The model predicts saturation excess and infiltration excess surface runoff and subsurface stormflow. Since the first article was published about the model in 1979 there have been many different versions. The idea has always been that the model should be simple enough to be modified by the user so that the predictions conform as far as possible to the user's perceptions of how a catchment works. The distributed outputs from the model help in such assessments.
TOPMODEL page at Lancaster University
GRASS man page r.topmodel
GRASS man page r.topidx
TopModel Bibliography

Storm water runoff: r.water.fea

r.water.fea is an interactive program that allows the user to simulate storm water runoff analysis using the finite element numerical technique. Infiltration is calculated using the Green and Ampt formulation. r.water.fea computes and draws hydrographs for every basin as well as at stream junctions in an analysis area. It also draws animation maps at the basin level. The software is available within GRASS 4.x/5.x.
r.water.fea developed at University of Oklahoma by Dr. B.E. Vieux
GRASS man page r.water.fea

Hydrologic modelling: r.hydro.CASC2D

CASC2D page at University of Connecticut
r.hydro.CASC2D is a physically-based, distributed, raster hydrologic model which simulates the hydrologic response of a watershed subject to a given rainfall field. Input rainfall is allowed to vary in space and time. Major components of the model include interception, infiltration, and surface runoff routing. Interception is a process whereby rainfall is retained by vegetation. Interception is estimated using an empirical three parameter model. Infiltration is the process whereby rainfall or surface water is pulled into the soil by capillary and gravity forces. The Green and Ampt equation with four parameters is applied to model the event-based infiltration. For continuous soil moisture accounting, redistribution of soil moisture can also be simulated whenever the non-intercepted rainfall intensity falls below the saturated hydraulic conductivity of the soil. The redistribution option requires two more soil hydraulic parameters. Excess rainfall becomes surface runoff and is routed as overland flow and subsequently as channel flow. The overland flow routing formulation is based on a two-dimensional explicit finite difference (FD) technique, while two different FD techniques, one explicit and one implicit, provide options for routing one-dimensional channel flow. Through a step function, a depression depth may be specified, below which no overland flow will be routed.
GRASS man page r.hydro.CASC2D

SWAT hydrologic model

The Soil and Water Assessment Tool (SWAT) is the hydrologic model used in the SWAT/GRASS linkage (USDA/Arnold and others, 1995). SWAT is a continuous-time, basin-scale hydrologic model capable of complex long-term simulations including hydrology, pesticide and nutrient cycling, and erosion and sediment transport. It is a river basin scale model developed to quantify the impact of land management practices in large, complex watersheds. SWAT is a public domain model actively supported by the USDA Agricultural Research Service at the Grassland, Soil and Water Research Laboratory in Temple, TX.

SWAT main page
Short SWAT-GRASS man page
Full SWAT-GRASS man page with references

Watershed Calculation: r.watershed

The series of programs provided within the watershed menu is effective for the delineation and segmenting of channel net- works, and for identifying a watershed boundary. Work is continuing to increase the effectiveness of delineating sub- basin boundaries as well.
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1.  Filtering of elevation data
2.  Locating pits
3.  Calculating drainage accumulation/outlining watershed
4.  Creating stream network
5.  Coding stream segments/finding segment lengths
6.  Finding subwatershed basins
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GRASS man page r.watershed

Floodplain Analysis: f.input etc.

f.input reads the results of the HEC-2 Water Surface Profile model and generates a vector map of water surface elevations at hydraulic sections. The user supplies to f.input a vector map of the hydraulic cross sections used in the HEC-2 model along with the HEC-2 model results.
f.econ takes as input the results of f.wsurf along with a user-supplied vector map of building sites and two ASCII files of economic data. As output f.econ generates a vector map of total damage to each building in the floodplain along with a summary ASCII report of flood damages categorized by building types (residential, public, ...) and damage type (structure or content). f.econ also reports areal extent of flooding.
f.reach provides floodwater statistics, including areal extent of flooding, average flood depth, and volume of water, calculated on a reach-by-reach basis.

Landscape Analysis: r.le

Since the 1970s, with the availability of satellite data, there has been an increasing interest in the structure of the earth on the scale of kilometers or hundreds of kilometers. Landscape ecology is a multi-disciplinary pursuit, involving geographers, biologists, sociologists, remote sensors, and many others. The focus of landscape ecology is on the dynamics and structure of the biosphere, including human activities, on the scale of hundreds of meters to kilometers (Risser et al. 1984; Forman and Godron 1986; Urban et al. 1987). The science of landscape ecology expanded rapidly in the 1980s, and methods for the quantitative analysis of landscape structure also were developed (e.g. Mead et al. 1981; Gardner et al. 1987; Milne 1988; Griffiths and Wooding 1988), yet there is no generally for the quantitative analysis of landscape structure that will work within a geographical information system (GIS). The r.le programs have been designed to provide software for calculating a variety of common quantitative measures of landscape structure. The programs can be used to analyze the structure of nearly any landscape.
The r.le programs are designed for analyzing landscapes composed of a mosaic of patches, but, more generally, these programs are capable of analyzing any two-dimensional raster or array whose entries are integer values. The r.le programs have options for controlling the shape, size, number, and distribution of sampling areas used to collect information about the landscape. Sampling area shapes can be square, or rectangular with any length/width ratio or can be circular with any radius. The size of sampling areas can be changed, so that the landscape can be analyzed at a variety of spatial scales simultaneously. Sampling areas may be distributed across the landscape in a random, systematic, or stratified-random manner, or as a moving window. The r.le programs can calculate a number of measures that produce single values as output (e.g. mean patch size in the sampling area), as well as measures that produce a distribution of values as output (e.g. frequency distribution of patch sizes in the sampling area) (Table 1), and it is also possible to output tables of data about selected attributes (e.g., size, shape, amount of perimeter) of individual patches, as well as to make new maps of patch attributes. The programs include no options for graphing or statistically analyzing the results of the analyses. External software must be used.

Postscript documentation (check also the related manual pages)

Wildfire spread simulation: r.ros/r.spread/r.spreadpath

This WIldfire SPread Simulation, WiSpS, package contains three GRASS programs r.ros, r.spread and r.spreadpath
r.ros (for wildfire spread simulation) - Generates three, or four raster map layers showing 1) the base (perpendicular) rate of spread (ROS), 2) the maximum (forward) ROS, 3) the direction of the maximum ROS, and optionally 4) the maximum potential spotting distance.
r.spread - Simulates elliptically anisotropic spread on a graphics window and generates a raster map of the cumulative time of spread, given raster maps containing the rates of spread (ROS), the ROS directions and the spread origins. It optionally produces raster maps to contain backlink UTM coordinates for tracing spread paths.
r.spreadpath - Recursively traces the least cost path backwards to cells from which the cumulative cost was determined.
GRASS man page r.ros
GRASS man page r.spread
GRASS man page r.spreadpath

Model integration in GRASS - Collection of Bernie Engel.

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