Calculates the ratio of the natural log of the specific catchment area contributing area to slope, lnas, or lnatan beta. The twi provides a more costefficient approach to flood determination than conventional hydrodynamic models. The computation of twi is performed using both geographic information systems gis and python, a programing software. On the calculation of the topographic wetness index hydrolearth. Using topographic wetness index in vegetation ecology. In my experience, this choice is crucial for the result. Topography wetness index application in floodriskbased. I know there are a lot of different way to estimate it. Information in a dem is stored in a gird format with values for elevation set for. Both inputs were derived from the pitremoved version of the 10 m resolution conditioned dtm dtm10condpr developed for mnmodel phase 4. Topographic position and landforms analysis the nature. Estimation of potential runoffcontributing areas in. Pdf on the calculation of the topographic wetness index. Here is a nice explanation provided by tom vanwalleghem to a similar thread on the gis stack exchange.
Numerical modelling of the topographic wetness index. Illinois state water survey contract report 201702, champaign, il seriesreport. The concept was first used in topmodel and further developed in the 1990s. 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.
Draw a line between the two points bounding the desired profile area. Topographic wetness index title topographic wetness index summary. Topography provides an alternative for mapping wetlands and. I expected that the resulting raster should look like and display index values like the following image in the pdf pdf, page 14. This may be useful when attempting to model ancient environments. Hodgson 1995 demonstrated that the slopes and aspects calculated from 30 m dems are representative of grid spacings two or three.
The jenness approach uses a multiscale approach by fitting a quadratic polynomial to a given window size using least squares. Evaluating topographic wetness indices across central new york. The preprocessed dem is used to calculate the predictor variables. Creating a topographic index so you can spend the next 3 yrs of you life figuring out what to do with it. Topographic wetness index urban flooding awareness act action. Pdf the topographic wetness index twi, lnatan beta, which combines local. Topographic wetness index and terrain ruggedness index length m maximum width m lw ratio height range m 28. The important parameters were then combined to produce a landslide susceptibility map. In addition, rsaga provides functions for importing and exporting different grid. In the research aim is to evaluate the jennes algorithm for landform classification in salt dome of korsia of darab plain, iran. The index is a function of both the slope and the upstream contributing area. Topographic wetness index and prehistoric land use abstract.
Topographic wetness index for jemez university of arizona. Which is the correct way to calculate the topographic. Moore et al 1993 examined the sensitivity of computed slope and steady state topographic wetness index values across 22 grid spacings for three moderately large. Topographic metrics to improve mapping of restorable. Linear models showed that elevation, slope, topographic wetness index, and tangential curvature could explain up to 21% of agb. Our analysis tested two topographic indices titopographic wetness index twi and sink depthboth calculated from high. Modifying digital elevation models to develop more. Description the topographic wetness index was computed using upstream accumulated areas or flow accumulation a and local slope b as twi lnatanb.
On the basis of this model, a topographic wetness index for a 10 x 10 m. 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. The twi has been used to study spatial scale effects on hydrological processes. This provides an indication of depth to water table.
Generating wetness indices for watersheds in grass cuosg. Pdf topographic wetness index explains soil moisture better than. The index is a function of both the slope and the upstream contributing area per unit width orthogonal to the flow direction. Wetness index aka compound topographic index, topographic wetness index, or topographic index. A comparison of the topographic wetness index and a. Epa region 10, working on the environmental monitoring and asssessment program western landscape project jones et al 2000. A new method for the determination of flow directions and upslope areas in grid digital elevation models, water ressources research, vol. A total of 12 thematic layers such as geology, geomorphology, land useland cover, lineament density, drainage density, rainfall, soil, slope.
Digital topographic and soil information was used to estimate potential runoffcontributing areas throughout kansas. A variety of landscape properties have been modeled successfully using topographic indices such as topographic wetness index twi, defined as lnatan. The topographic wetness index is a method used to monitor rainfall and runoff. It is commonly used to quantify topographic control on hydrological processes. Landform classification using topography position index. On the other hand, if the majority of creeks, streams, and swampy areas on the topographic map are shown to be dry areas on the wetness index, the index is likely inaccurate. Pdf on jun 23, 2017, malgorzata radula and others published topographic wetness index explains soil moisture better than bioindication. Topmodel simulations of streamflow and depth to water table in fishing brook. 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. Topographic wetness index and terrain ruggedness index in. A screenshot during wetness index from 5x5 average filtered dem x5times verification, in the northern region of the carp watershed. Twi was created by running the topographic wetness index tool in taudem, and used both a specific catchment area grid and flow direction grid as inputs.
The training data are coupled with the merged predictor variables to train a random trees breiman, 2001 model. On the pasda pamap program lidar las files data summary web page, click. The topographic wetness index twi was developed by beven and kirkby 1979 within the runoff model topmodel. Gis and ahp techniques based delineation of groundwater. Topographic wetness index geonet, the esri community. 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. 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. What is the typical topographic wetness index range of. Predicting aboveground forest biomass with topographic. Then i calculated the topographic wetness index, but the results look very mixed somewhere between a rainbow and random fuzzy bits and values are always negative. Integrating terrain and vegetation indices for identifying. This report describes the theoretical basis for the calculation of the stability index, describes the implementation, presents several. The basics topographic maps produced by natural resources canada nrcan offer detailed information on a particular area and are used for several types of. In this study, 25 m spatial resolution from digital elevation models dem data were used to investi.
Thus it can provide indirect information on land cover and agricultural potential. I have filled and projected my digital terrain model to obtain with the hydrology tool. Training data are derived from the ground truth data. Local mean elevation is subtracted from the elevation value at centre of the local window. The usefulness of a topographic index approach as a basis for aggregation of svat or ecological models over large areas depends on how well the spatial distribution of wetness is captured by the topographic index. A physicallybased variable contributing area model of basin hydrology. 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 wetness index the twi is a physically based index or indicator of the effect of local topography on runoff flow direction and accumulation. Potential runoffcontributing areas were estimated collectively for the processes of infiltrationexcess and saturationexcess overland flow using a set of environmental. Topographic wetness index and terrain ruggedness index in geomorphic characterisation of landslide terrains, on examples from the sudetes, sw poland. Exploring the application of topographic indices in urban. The topographic wetness index twi has become a widely used tool to describe wetness conditions at. Input data for landform classification is digital elevation model dem with resolution.
No data values occur in locations where slope is 0 flat. The results then were used to compare 91 selected subbasins representing soil, slope, and runoff variability. Gis topographic wetness index twi susquehanna river basin. 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 topographic wetness index twi, also known as the compound topographic index cti, is a steady state wetness index. Slope angle and distance to streamlake were found to be the most important parameters along lake champlain shoreline. 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. Mapping of hydropedologic spatial patterns in a steep.
Improve the current wetland mapping process through decreased production time and increased accuracy a ff f h iassess effects of human impacts improve targeting of wetland restoration. We obtained nuisance flood reports from the municipal data service 311 for several watersheds in new york city and baltimore, usa. This information can be used to ma p current and historic wetlands. Lidar based topographic metrics map potential wetness based on topographic position. 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. Module topographic wetness index twi sagagis module. From each mark, indicate the vertical height with a dot on a. Compound topographic index anthropology analytical.