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. If not stated otherwise, all content is licensed under creative commons attributionsharealike 3. Description the topographic wetness index was computed using upstream accumulated areas or flow accumulation a and local slope b as twi lnatanb. This family of indices may improve our ability to model the habitat of wetlands species. I would appreciate using saga or qgis, but i also have arcgis 9 at hand. Topographic wetness index and prehistoric land use abstract.
On the calculation of the topographic wetness index. In humid areas, topographic wetness indices twis are widely applied to estimate relative soil moisture patterns. What is the typical topographic wetness index range of values. The process calculate the difference between elevation at a specific cell and the average elevation in. The morphometry tools are unique including the saga topographic wetness index and topographic position classification. 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. Using lidarmodified topographic wetness index, terrain. Integrating all this information the contrast index map was obtained, which once reclassified, allowed the spatial delineation of the flood scenarios and their categories of susceptibility. Which is the correct way to calculate the topographic. Topographic wetness index abstract the topographic wetness index, coined by beven and kirkby in 1979, aims to quantify the influence of topography on hydrological processes within a watershed. Creates topographic index lnatanbeta map from elevation map topographic wetness index. Download indexes in shapefile and geodatabase formats through the national map download client. Topographic wetness index aka wetness index aka compound topographic index a measure of water accumulation or soil saturation calculated as.
The topographic wetness index twi module requires a normal slope grid as input. The units of upslope contributing area are m2m or m in fact a is as or specific contributing area, contributing area per unit contour width so thats why you multiply by cell resolution 30 m and not by cell area 3030 a more correct way to calculate this would be to take into account. Exploring hydrological analyses using saga gis cuosg. Dec 17, 2011 compound topographic index cti moore et al. Jul 29, 2019 the topographic wetness index one step tool is a tool chain, in which the dem is preprocessed with the sink removal tool and the slope is computed using the slope, aspect, curvature tool, then the twi is computed using the following tools in sequence. Installing the topographic wetness index python script into. Through the application of spatially distributed models, the topographic wetness index twi can be determined as an alternative to the traditional approach of delineating floodprone areas using contours alone. Apr 08, 2017 installing the topographic wetness index python script into an arcgis toolbox. Compound topographic index anthropology analytical.
Topographic position and landforms analysis the nature. If you have a dem, and dont know what to do with it you need to look at saga gis. First, introduced by beven and kirkby 1979, it has been used in various ecological studies and has proven usefulness. Scinetnathaz project progress meeting 2326 oct 2014, burgas, bulgaria konstantinos papatheodorou helena tzanou tei of kentriki makedonia, lpenpi beneficiary. Calculates the ratio of the natural log of the specific catchment area contributing area to slope, lnas, or lnatan beta. Which is the correct way to calculate the topographic wetness. However, it generally correctly predicts the accumulation of flow in topological low spots e. Greetingsi am new with saga gis, so far finding it interesting. Creates vector maps of lines and points of continuously lowering elevation down the input watercourses, based on the input raster dem. Since its introduction, the twi concept has been integrated into many popular hydrologic models e. Saga geoprocessing and terrain analysis in r description rsaga provides direct access to saga gis functions including, for example, a comprehensive set. Scinetnathaz project progress meeting using morphometric. Topography wetness index application in floodriskbased. The topographic wetness index one step tool is a tool chain, in which the dem is preprocessed with the sink removal tool and the slope is computed using the slope, aspect, curvature tool, then the twi is computed using the following tools in sequence.
The topographic wetness index twi is one of the most widely used topographybased indications of soil moisture. Package rsaga november 12, 2018 type package title saga geoprocessing and terrain analysis version 1. In my new employment i was requested to calculate twi so i was a bit confused as to which approach to use in saga because there is basic terrain analysis, twi, twi one step and saga wetness index. Introduction soil moisture is a key variable controlling hydrological and biogeochemical processes buchanan et al. Calculate the topographic wetness index in qgis duration. Normalized difference vegetation index ndvi geogrphic informations system arcgis esri gis. Topography position index tpi landform slope classification standardization neighborhood statistics. As an example, consider a location in a meadow in yosemite valley. A comparative assessment of prediction capabilities of. Thus, the index may not capture conditions in areas where there are other more dominant processes governing the flow. Here is a nice explanation provided by tom vanwalleghem to a similar thread on the gis stack exchange.
In neuroscience, the neuroimaging discipline uses techniques such as eeg topography for brain mapping. 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 twi has been used to study spatial scale effects on hydrological processes. This dataset represents the steady state wetness index computed by d8 and dinfinity flow models and is intended for the visualization and support topographic and geospatial analysis. On the basis of this model, a topographic wetness index for a 10 x 10 m. The twi provides a more costefficient approach to flood determination than conventional hydrodynamic models. This may be useful when attempting to model ancient environments.
Terrain metrics and landscape characterization from. Topography has been applied to different science fields. How to calculate topographic wetness index using arcgis. The topographic wetness index twi, also known as the compound topographic index cti, is a steady state wetness index. For arcgis users, portions of this tool have been rewritten and are available in the arcgis land facet corridor designer extension. In ophthalmology, corneal topography is used as a technique for mapping the surface curvature of the cornea. Topographic wetness index raster console usage processing. Topographic position is an inherently scaledependent phenomenon. The topographic wetness index is a method used to monitor rainfall and runoff.
The topographic wetness index twi was developed by beven and kirkby 1979 within the runoff model topmodel. Creating a topographic index so you can spend the next 3 yrs of you life figuring out what to do with it. For the intensitybased ici, no empirical value was available from the nordic countries, so a default. In order to test the giss in solving a complex task, we chose the topographic wetness index twi. Go to the usgs store and select mapsstate topographic map indexes. Understanding the spatial distribution of hydrologic. This may be an appropriate scale for looking at soil transport or site water balance. A physically based variable contributing area model of basin hydrology. Installing the topographic wetness index python script. Jan 30, 20 topographic wetness index appears as an informative predictor of species occurrence, at least for the whinchat, and a useful proxy to detect suitable areas for floodplain grassland birds. I expected that the resulting raster should look like and display index values like the following image in the pdf pdf, page 14. Saga algorithm provider terrain hydrology if not stated otherwise, all content is licensed under creative commons attributionsharealike 3. In its basic form, it works by deriving slope and accumulation distribution parameters from a topographic model sorensen et al.
I have filled and projected my digital terrain model to obtain with the hydrology tool. A total 11 landslide conditioning factors are considered such as slope angle, aspect, altitude, distance from drainage, distance from road, distance from river, lithology, land use, topographic wetness index, stream power index and slopelength ls. Topographic wetness index predicts the occurrence of bird. Topographic wetness index title topographic wetness index summary. Landform classification for site evaluation and forest. At a fine scale of 100m, the topographic position would be a flat plain. No data values occur in locations where slope is 0 flat. Scinetnathaz project progress meeting 2326 oct 2014, burgas, bulgaria. Consider saga gis a prime choice for environmental modeling and other applications. Topographic wetness index and terrain ruggedness mafiadoc.
Sti is based on the topographic index ti introduced by beven and kirkby, 1979 and spatial variation in hydrologically relevant soil properties. Sti is one of the popular methods to calculate twi. Jan 26, 2019 calculate the topographic wetness index in qgis duration. Topographic wetness index and terrain ruggedness index length m maximum width m lw ratio height range m 28. Flow accumulation topdown, flow width and specific catchment area, topographic wetness. 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. Thus it can provide indirect information on land cover and agricultural potential. Calculate topographic wetness index in saga stack overnet. 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. Topographic position index the analysis was performed trough the simulation of dtm to obtain topographic position index tpi in morphometry module within saga gis. I know there are a lot of different way to estimate it. Topographic wetness index appears as an informative predictor of species occurrence, at least for the whinchat, and a useful proxy to detect suitable areas for floodplain grassland birds. Topographic indices assume that topography drives flows.
Installing the topographic wetness index python script into an arcgis toolbox. In addition, rsaga provides functions for importing and exporting different grid. The index is a function of both the slope and the upstream contributing area per unit width orthogonal to the flow direction. This provides an indication of depth to water table. A new topographic index to quantify downslope controls on local drainage. Order a paper topographic map index for any state or download a free pdf. Has someone here experience with the quantification of topographic wetness in an area and could provide a tutorial how to do it right. What is the typical topographic wetness index range of.
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