Forests in three different regions of the czech republic. 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. As an important topographic attribute widelyused in precision agriculture, topographic wetness index twi is designed to quantify the effect of local topography on hydrological processes and for modeling the spatial distribution of soil moisture and surface saturation. For the twi to be meaningful this raster should have a resolution of a least 30m.
Estimation of potential runoffcontributing areas in. Thus it can provide indirect information on land cover and agricultural potential. These supplement volumes are abstracted and indexed the same way the main volumes are. The topographic position index tpi compares the elevation of each cell in a dem to the mean elevation of a specified neighborhood around that cell fig. Lnatanb based on the idea of beven and kirkby 1979 where. Lidar makes calculation of twi possible in areas of low. The topographic wetness index twi, also known as the compound topographic index cti. The topographic wetness index, coined by beven and kirkby in 1979, aims to quantify the influence of topography on hydrological processes within a watershed. Topography wetness index application in floodriskbased. On the calculation of the topographic wetness index hydrolearth. 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. Topographic wetness indextopographic wetness index twi lna s tan. The computation of twi is performed using both geographic information systems gis and python, a programing software. The topographic wetness index twi was developed by beven and kirkby 1979 within the runoff model topmodel.
Topographic wetness index explains soil moisture better than bioindication with ellenbergs indicator values. Topographic wetness index explains soil moisture better. How to install the twi python script into an arcgis toolbox. 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.
In this example an annulus neighborhood is used, but continuous circles or other shapes could be used. Pdf topographic wetness index explains soil moisture better than. It is commonly used to quantify topographic control on hydrological processes. I expected that the resulting raster should look like and display index values like the following image in the pdf pdf, page 14. As an important topographic attribute widelyused in precision agriculture, topographic wetness index twi is designed to quantify the effect of local topography on hydrological processes and for modeling the spatial distribution of soil moisture. The index is a function of both the slope and the upstream contributing area. This index is formulated as twi lnatanb, where a is the upslope.
Juracek abstract digital topographic and soil information was used to estimate potential runoffcontributing areas throughout kansas. 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 wetness index twi and terrain ruggedness index tri are secondary geo morphometric parameters used to describe and quantify local relief. Installing the topographic wetness index python script. Topographic wetness index urban flooding awareness act action. 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. Illinois state water survey contract report 201702, champaign, il seriesreport.
Thus, the index may not capture conditions in areas where there are other more dominant processes governing the flow. The topographic wetness index twi, frequently used in approximately characterizing the spatial distribution of soil moisture and surface saturation within a watershed, has been widely applied in topographyrelated geographical processes and hydrological models. As such, in this paper, the steadystate topographic wetness index was used to represent the spatial distribution of water flow and water stagnating across the country. Which flow routing algorithms are preferable for application in vegetation ecology. Topographic wetness index and terrain ruggedness index in. This index was first developed by beven and kirkby 1979 within their physically based runoff model, topmodel, which is based on the. We used vegetation data from 521 georeferenced plots, recently sampled in a wide. Abstract as an important topographic attribute widelyused in precision agriculture, topographic wetness index twi is designed to quantify the effect of local topography on hydrological processes and for modeling the spatial distribution of soil moisture and surface saturation. Twi beven and kirkby, 1979 relates upslope area as a measure of water flowing towards a certain point, to the local slope. A topographic wetness index is based on the idea that a terrain profile controls the distribution of water and areas subject to water accumulation. Description the topographic wetness index was computed using upstream accumulated areas or flow accumulation a and local slope b as twi lnatanb. Topographic wetness index explanation for forsythe ii mmg.
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. Identification of surface water storing sites using. Pdf on jun 23, 2017, malgorzata radula and others published topographic wetness index explains soil moisture better than bioindication. Topographic wetness index that is purely based on topography is a function of the upstream contributing area and slope 1719. The topographic wetness index twi, also known as the compound topographic index cti, is a steady state wetness index. Generating wetness indices for watersheds in grass cuosg. Topographic indices assume that topography drives flows. Topographic wetness index and prehistoric land use abstract. Modifying digital elevation models to develop more. Compound topographic index anthropology analytical. Estimation of potential runoffcontributing areas in kansas using topographic and soil information by kyle e. Using topographic wetness index in vegetation ecology. 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.
Unmapped special flood hazard areas sfha pdf destined for dfirms stream studies becoming flood maps. 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. However, it generally correctly predicts the accumulation of flow in topological. Topographic wetness indices twis computed from digital elevation models dems are means to forecast the amount of moisture in the soil. Features are shown as points, lines, or areas, depending on their size and extent. How important is the choice of flow routing algorithm with respect to application of topographic wetness index twi in vegetation ecology. Nfhl viewer more detailed flood data displays when zoomed in. This recipe shows you how to calculate a popular one, which is called the topographic wetness index, which. 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. A variety of landscape properties have been modeled successfully using topographic indices such as topographic wetness index twi, defined as lnatan. Flow accumulation topdown, flow width and specific catchment area, topographic wetness.
Superimpose the wetness index image with the transparency of 60% over the topographic map. A comparison of the topographic wetness index and a. 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. In order to test the giss in solving a complex task, we chose the topographic wetness index twi. 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. The twi provides a more costefficient approach to flood determination than conventional hydrodynamic models. Topographic wetness index the twi is a physically based index or indicator of the effect of local topography on runoff flow direction and accumulation. 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. Thematic supplements zfg regularly publishes thematic supplements. This may be useful when attempting to model ancient environments. Pdf an approach to computing topographic wetness index. Numerical modelling of the topographic wetness index.
Develop gis topographic wetness index maps conduct well emplacement develop spatial distribution plan for treecore sampling begin sampling begin sampling of treecores begin soil wetness measurements and correlate to gis data july 20 continue sampling extract majority of treecores for later data processing continue soil wetness. 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. Conference describing the concept of topographic position index tpi and how it could be calculated weiss 2001. An approach to computing topographic wetness index based. Both inputs were derived from the pitremoved version of the 10 m resolution conditioned dtm dtm10condpr developed for mnmodel phase 4.
On the basis of this model, a topographic wetness index for a 10 x 10 m. Geological survey reading topographic maps interpreting the colored lines, areas, and other symbols is the. The twi has been used to study spatial scale effects on hydrological processes. The index is a function of both the slope and the upstream contributing area per unit width orthogonal to the flow direction. Using this tpi at different scales, plus slope, users can classify the landscape into both slope position i. Topographic wetness index and terrain ruggedness index length m maximum width m lw ratio height range m 28. Wetness index aka compound topographic index, topographic wetness index, or topographic index. How important is the choice of flow routing algorithm with respect to application of topographic wetness index twi in vegetation. On the calculation of the topographic wetness index. Gis topographic wetness index twi susquehanna river basin.
Provided for noncommercial research and educational use. An approach to computing topographic wetness index based on maximum downslope gradient. Topographic position and landforms analysis the nature. In this study, 25 m spatial resolution from digital elevation models dem data. Topographic wetness index is used to quantify topographic controls on hydrological processes. Topographic wetness index urban flooding awareness act.