Creating a topographic index so you can spend the next 3 yrs of you life figuring out what to do with it. I am trying to calculate the topographic wetness index one step using the rsaga. Module topographic wetness index twi sagagis module. As a consequence, a wide range of topographybased wetness indices have been. Thus, the index may not capture conditions in areas where there are other more dominant processes governing the flow. Miscalculated topographic wetness index geonet, the esri. The input file is a dem with 10m spatial resolution. Pdf using topographic wetness index in vegetation ecology. Add the following natural logarithm ln equation in the expression window. Input data for landform classification is digital elevation model dem with resolution.
Superimpose the wetness index image with the transparency of 60% over the topographic map. How important is the choice of flow routing algorithm with respect to application of topographic wetness index twi in vegetation. The jenness approach uses a multiscale approach by fitting a quadratic polynomial to a given window size using least squares. The topographic wetness index twi was developed by beven and kirkby 1979 within the runoff model topmodel. Modifying digital elevation models to develop more realistic. For every point in a digital elevation model dem, you can compute a number of parameters that represent the change in surface relative to neighboring. The topographic wetness index twi, also known as the compound topographic index cti, is a steady state wetness index. In arctoolbox, spatial analyst tools toolbox, map algebra toolset, open the raster calculator geoprocessing tool 74. Tpi stands for topographic position index, which is defined as the difference between a central pixel and the mean of its surrounding cells. This may be useful when attempting to model ancient environments. Landform classification using topography position index. If digital topographic maps are available in your area, they can provide a good means of evaluating the potential accuracies of your output wetness index images. The paper discusses the question whether geographical information systems gis and digital elevation models dem are useful tools for studying correlations between topographic attributes of a given area, and vascular flora requirements reflected by ecological indicator values eivs.
In this study, 25 m spatial resolution from digital elevation models dem data. I am trying to use a flow accumulation fac raster and a slope slope raster to calculate the topographic wetness index twi in raster calculator as. As the topography defines and influences most of the processes that take place in a given terrain, the dem can be used to extract many different parameters, which give us information about these processes. Topographic wetness index and prehistoric land use abstract. Landform classification using topography position index case.
Topographic maps and countours academic resource center. The computation of twi is performed using both geographic information systems gis and python, a programing software used to enhance computing capabilities. Using compound topographic index to delineate soil landscape facets from digital elevation models for comprehensive coastal assessment yang, x. The distribution and frequency of the obtained topographic wetness index is shown in fig. This section provides an overview of slope, aspect, and other parameters that are used in topographic modeling. The area with empty cells is near the right margin of the raster. The topographic wetness index twi is frequently used to simulate the soil moisture conditions in a watershed quantitatively, and it is the most commonly an improved topographic wetness index considering topographic position ieee conference publication.
Lnfactanslope the resulting output values do not make sense relative to hand calculations. Machineaccessible metadata file describing the reported data isatab format. It is commonly used to quantify topographic control on hydrological processes. Is there any option to saga to calculate the topographic wetness index. Generating wetness indices for watersheds in grass cuosg. The landform classification is done using the jenness algorithm, based on the tpi of the area under studykerala state, india. On the calculation of the topographic wetness index hydrolearth. A revised version of the topographic wetness index written for arcpython africkertopographic wetnessindex. The saga wetness index is, as the name says, similar to the topographic wetness index twi, but it is based on a modified catchment area calculation modified catchment area, which does not think of the flow as very thin film. Topographic maps represent the earths features accurately and to scale on a twodimensional surface.
Using topographic wetness index in vegetation ecology. Which is the correct way to calculate the topographic. You need to enter the path name for the folder containing the tabular data, e. The twi has been used to study spatial scale effects on hydrological processes. Which is the correct way to calculate the topographic wetness index with arcgis. For a more detailed background, consult the references at the end of this topic. Find file copy path topographicwetnessindex twifilledplus0. Forests in three different regions of the czech republic. Originally developed in the topmodel framework beven et al. Local mean elevation is subtracted from the elevation value at centre of the local window.
Hydrology research group terrain analysis using digital elevation models taudem. In this study, 25 m spatial resolution from digital elevation models dem data were used to investi. What is the typical topographic wetness index range of. Stockholm university, faculty of science, department of physical geography and quaternary geology. The highest twi is found in relatively flat areas that can easily accumulate water. I have a big area and i tried many times with saga, the last time i thought the results was ok before saga would crash or g. Topographic wetness index wti the topographic wetness index wti, extends the purely topographybased twi by accounting for spatial variation in hydrologically relevant soil properties beven, 1986 and beven and kirkby 1979.
The index is a function of both the slope and the upstream contributing area per unit width orthogonal to the flow direction. Using topography position index for landform classification. A digital terrain model dtm of an area of approximately 100 km2 in east jutland, denmark, has been created based on information from the oldest available topographic map from the second half of the 19th century. The minimum, the maximum and the average of twi is 0, 28 and 4. In arc catalog create a new shapefile under file new, make it a point file. On the calculation of the topographic wetness index. Everything works fine for small areas, but if i try to do this for larger areas the process crashes. In the research aim is to evaluate the jennes algorithm for landform classification in salt dome of korsia of darab plain, iran. It makes use of an index of hydrological similarity based on topographic data. They concluded that the bayesian updating procedure was useful for computing the topographic wetness index threshold. Wetness index is calculated based on wetnessindexln atanb where a represents the upslope contributing area and b represents slope.
A variety of landscape properties have been modeled successfully using topographic indices such as topographic wetness index twi, defined as lnatan. After starting arcview, load the extension by clicking on file extensions, scrolling. For the last twi created in saga i decided to calculate the slope also in saga, but i still have problems with the file. Getting ready open the dem that we prepared in the preparing elevation data recipe. Topographic index maps are grids derived from digital elevation models dems. A comparison of the topographic wetness index and a dynamic distributed model. Pdf the topographic wetness index twi, lnatan beta, which combines local upslope contributing area and slope, is commonly used to quantify. What is the typical topographic wetness index range of values. Using compound topographic index to delineate soil. Title topographic wetness index summary calculates the ratio of the natural log of the specific catchment area contributing area to slope, lnas, or lnatan beta.
Gis topographic wetness index twi susquehanna river basin. This study is an attempt to classify the topographic position index tpi and landforms of kerala state, india using complex spatial statistics and gis application to identify and extract geomorphologic properties of digital elevation model with 30 m resolution. In its basic form, it works by deriving slope and accumulation distribution parameters from a topographic model sorensen et al. This recipe shows you how to calculate a popular one, which is called the topographic wetness index, which estimates the soil wetness based on the topography. Schematic diagram of morphology types used to compile topographic wetness index the process described herein uses a type of digital terrain analysis dta resulting in a topographic wetness index twi that quantifies topographic controls of basic hydrological processes schillaci et al.
This method was further developed by weiss and jenness. Which flow routing algorithms are preferable for application in vegetation ecology. Evaluation of integrating topographic wetness index with. Thus it can provide indirect information on land cover and agricultural potential. The spatial resolution of dems is a major influence on the values of indices such as topographic wetness index, derived from numerical models. By nrcs soil scientists tom davello, joe brennan, and lynn loomis. Mean elevation is subtracted from the elevation value at center. I just open a 300 mb tiff file in saga gis without problems. This python script can be imported to create a twi tool. In addition, rsaga provides functions for importing and exporting different grid. However, it generally correctly predicts the accumulation of flow in topological low spots e.
This script was written to be used as a tool in arcgis. Newest topographicwetnessindex questions geographic. Methods of computing this index differ primarily in the way the upslope contributing area is cal. Background performing additional processes on digital elevation models is a common practice. Modifying digital elevation models to develop more realistic wetness index layers for soil. Numerical modelling of the topographic wetness index. Topographic maps are an excellent planning tool and guide and, at the same time, help make outdoor adventures enjoyable and safe. Topographic wetness index urban flooding awareness act action. Using compound topographic index to delineate soil landscape. Topographic wetness index twi that quantifies topographic controls of. The topographic wetness index, coined by beven and kirkby in 1979, aims to quantify the influence of topography on hydrological processes within a watershed. Topographic position index tpi is an adaptation of this method which compares the elevation of each cell in a dem to the mean elevation of a specified neighborhood around that cell. We used vegetation data from 521 georeferenced plots, recently sampled in a wide.
Topographic wetness indices twis computed from digital elevation models dems are means to forecast the amount of moisture in the soil. Dec 17, 2011 compound topographic index cti moore et al. In this study, 25 m spatial resolution from digital elevation models dem data were used to investigate the scaledependency of twi values when converting dems to 50 and 100 m. Newest topographic wetness index questions feed to subscribe to this rss feed, copy and paste this url into your rss reader. Sagagis topographic wetness index topowetnessindex. Modifying digital elevation models to develop more. In my experience, this choice is crucial for the result.
Estimation of potential runoffcontributing areas in. Draw a line between the two points bounding the desired profile area. Topographic indices assume that topography drives flows. Dec 01, 2019 sagagis topographic wetness index topowetnessindex. Parameters slope raster catchment area raster transmissivity raster. Majid hojati tehran university, department of gis and remote sensing, tehran, iran majid. Topographic attributes and ecological indicator values in. This is how it looks like black cells are nodata cells. Modifying digital elevation models to develop more realistic wetness index layers for soil survey applications.
The process described herein uses a type of digital terrain analysis dta resulting in a. Topographic wetness index can be expressed as lnatanb based on the idea of beven and kirkby 1979 where a is the specific catchment area aal, catchment area adivided by contour length. Topographic wetness index predicts the occurrence of bird species. Compound topographic index anthropology analytical. Estimation of potential runoffcontributing areas in kansas using topographic and soil information by kyle e. The index is a function of both the slope and the upstream contributing area. Conference describing the concept of topographic position index tpi and how it could be calculated weiss 2001. Topographic wetness index the twi is a physically based index or indicator of the effect of local topography on runoff flow direction and accumulation. Gray new south wales department of natural resources dnr, po box 3720, parramatta nsw 2124, email. Nov 19, 2015 the topographic position index tpi guisan et al. A suite of global, crossscale topographic variables for. The computation of twi is performed using both geographic information systems gis and python, a programing software.
On the basis of this model, a topographic wetness index for a 10 x 10 m. Ks so that the soiltopographic wetness index stwi can be expressed as. Pdf on the calculation of the topographic wetness index. Topographic wetness index is calculated as ti lnupslope contributing area tanof slope angle the upslope area is the flow accumulation map, you can calculate this map using arcgis hydrology. Import into arc map and digitize a point at the outlet of the watershed. Topographic wetness index twi was developed to locate wetlands but has largely been ignored from ecological studies despite the value of these areas for. Twi beven and kirkby, 1979 relates upslope area as a measure of water flowing towards a certain point, to the local slope. Calculates the ratio of the natural log of the specific catchment area contributing area to slope, lnas, or lnatan beta. Topographic wetness index title topographic wetness index summary. Juracek abstract digital topographic and soil information was used to estimate potential runoffcontributing areas throughout kansas. Contour map characteristics index contours are used to label the elevation of the their associated points.
A comparison of wetness indices for the prediction of observed. This command outputs a singleband raster with values computed from the elevation. This provides an indication of depth to water table. It affects the spatial distribution of soil moisture, and groundwater flow often follows surface topography burt and butcher, 1986. Inputs are the workspace and the input dem, output is the twi layer we chose to fill all sinks due to some small sinks in a lidar redived dem.
160 528 1040 1115 1009 63 1324 405 1407 791 946 172 946 757 360 1007 325 957 30 727 1529 1378 1240 213 199 248 1290 60 1231 630 1088 70 1165 227 1379 1035 901 290 277