WMS-Watershed Modeling System
Watershed Modeling System with HEC-1
WMS is a state-of-the-art computer program which utilizes digital terrain data to delineate watershed and sub-basin boundaries and compute geometric parameters used in hydrologic modeling. WMS includes tools which aid in the creation of both rural and urban watersheds with interfaces to hydrologic modeling software. WMS includes the actual models as well as the interfaces.
HEC-1 Interface in WMS
WMS includes a comprehensive interface to the HEC-1 flood hydrograph program used by many hydrologic engineers to model the rainfall-runoff process. The interface has been created in such a way that models can be built from TINs used to delineate basin boundaries and compute geometric data, or by manually constructing a series of outlets and basins to form a topologic representation of the watershed. When a TIN is used the topologic model is automatically constructed as outlets are added and basins defined. Furthermore any geometric parameters computed by WMS are supplied to corresponding HEC-1 input fields.
HEC-1 parameters are edited from a master dialog, which displays the currently defined data of a selected basin or outlet (in HEC card style format) and allows the user access to the several user-friendly dialogs used to specify desired options. WMS includes the ability to define several of the advanced HEC-1 options such as time-area curves, lag times and times of concentration, and snow melt elevation zones using computed geometric parameters.
Once a HEC-1 model has been defined the HEC-1 model checker can be run to try and identify potential problems in the data prior to actually running the HEC-1 model. The model checker provides several hints (although it does not guarantee a successful run or that the answers will be correct) for correcting the data prior to running HEC-1.
HEC-1 can be launched from within WMS and after completion hydrographs can be displayed in the hydrograph window. Hydrographs from different sub basins or from different runs of HEC-1 can also be overlaid for comparison.
Sub-basins of the watershed can be created by adding any number of additional outlet points along the stream network. Besides the sub-basin boundaries, WMS automatically creates a topologic representation of the watershed which is used for defining models such as HEC-1 and TR-20.
TR-20 Interface in WMS
WMS includes a comprehensive interface to the TR-20 hydrologic program used by many hydrologic engineers to model the rainfall-runoff process. The interface has been created in such a way that models can be built from TINs used to delineate basin boundaries and compute geometric data, or by manually constructing a series of outlets and basins to form a topologic representation of the watershed. When a TIN is used the topologic model is automatically constructed as outlets are added and basins defined. Also, any geometric parameters computed by WMS are supplied to corresponding TR-20 input fields.
TR-20 parameters are edited from a master dialog. This dialog allows the user access to the several user-friendly dialogs, including the channel data dialog, used to specify desired options. WMS allows the user to define the main TR-20 options such as the RUNOFF, REACH, RESVOR, and DIVERT cards. Composite curve numbers and basin times of concentration can be computed automatically.
Once a TR-20 model has been defined the TR-20 model checker can be run to try and identify potential problems in the data prior to actually running the TR-20 model. The model checker provides several hints (although it does not guarantee a successful run or that the answers will be correct) for correcting the data prior to running TR-20.
TR-20 can be launched from within WMS and after completion hydrographs can be displayed on the TIN, the topologic model and blown up within the hydrograph window.
Interface to NFF in WMS
The National Flood Frequency (NFF) Program was developed by the USGS in cooperation with the Federal Highway Administration (FHA) and the Federal Emergency Management Agency (FEMA). It evaluates regression equations for estimating T-year flood-peak discharges for rural and urban watersheds. As many as 7 multiple regression equations (2-, 5-, 10-, 25-, 50-, 100-, and 500-year) are defined for each of 200 plus flood regions across the US. Methods are also available for estimating a typical flood hydrograph corresponding to a given T-year peak discharge.
The NFF program is composed of two components: (1) Each state's regression equations, standard errors, etc., and (2) a calculation routine for rural and urban flood characteristics, including tabling and graphing capabilities. To use the regression equations a basin is defined in WMS using the TIN and drainage analysis tools for basin delineation. The NFF main dialog is then used to define the state and region(s) where the watershed is located. Variables for the regression equations are then defined and peak flows computed. NFF has the capability to generate an approximate, design hydrograph which can be displayed within WMS in the same way hydrographs for HEC-1 and TR-20 are displayed.
Interface to the Rational Method in WMS
The Rational Method is one of the simplest and best known methods routinely applied in urban hydrology. Peak flows are computed from the simple equation: Q = kCiA where: Q - Peak flow, k - conversion factor, C - Runoff coefficient, i - Rainfall intensity, A - Catchment area.
With WMS' capability to create TINs from feature arc data, roads, railroads, canals, and other urban features which control runoff are easily incorporated into the model so that an urban catchment areas can be delineated so that the variable A can be automatically computed.
The Rational method main dialog includes the capability to generate Intensity-Duration-Frequency (IDF) curves from HYDRO-35 maps (eastern US), NOAA Atlas maps (western US), or user specified data of rainfall intensities. A kinematic wave equation, used by the Federal Highways Administration (FHA) design handbook, can be used to estimate the time of concentration from the catchment length, slope, and a Manning's roughness coefficient.
Digital Terrain Modeling and Mapping
Watershed models can be created in WMS from: triangulated irregular networks (TINs), Digital Elevation Models (DEMs), or GIS vector data. WMS is compatible with ARC/INFO and ArcView data and includes many utilities for both importing and exporting. Major features of WMS include:
- Watershed model development from imported ARC/INFO or ArcView shape files.
- Delineates watershed and sub-basin boundaries from TINs or GRIDs.
- Computes geometric parameters in a fraction of the time required from traditional methods.
- Complete Interfaces to HEC-1, TR-20, Rational Method, and NFF.
- Composite curve number generation from GIS vector or grid data.
- Automatic computations of time of concentration or lag time from computed geometric parameters.
- Flood plain delineation.
- Use of TIFF images as backdrops for on-screen digitizing or to enhance final presentation graphics.
- Hydrologic/hydraulic calculators for detention basin, curb and gutter, wire, and improved channels.
Overview of WMS
WMS merges information obtained from terrain models and GIS with industry standard lumped parameter hydrologic analysis models such as HEC-1 and TR-20. Terrain models can obtain geometric attributes such as area, slope and runoff distances. Many display options are provided to aid in modeling and understanding the drainage characteristics of terrain surfaces.
The distinguishing difference between WMS and other applications designed for setting up hydrologic models like HEC-1 and TR-20 is its unique ability to take advantage of digital terrain for hydrologic data development. WMS uses three primary data sources for model development:
1. Geographic Information Systems (GIS) Data
2. Digital Elevation Models (DEMs)
3. Triangulated Irregular Networks (TINs)
Guidelines for Using Geographic Information Systems (GIS) Data
Watershed and sub-basin boundaries may already be known and stored as part of a GIS or CAD database, or it may be straight- forward to trace an existing map to define streams and basins. With WMS, properly structured hydrologic models can be created automatically from points, lines, and polygons.
Since this data is often already developed and stored in a GIS, importing from ARC/INFO and ArcView, or DXF files is easily done.
The following are the basic steps required to create watershed models from scratch using GIS data.
1. Obtain a Map or Already Developed GIS or CAD Data or digitize a TIFF image of a map on screen.
2. Construct Feature Object Topology
3. Define the Hydrologic Model
Topologic model automatically constructed from feature objects.
Guidelines for Using DEM Data
One way WMS can be used for defining watershed models and developing hydrologic data involves the use of digital elevation models or DEMs. A DEM is a two-dimensional array of elevation points with a constant x and y spacing. Their simple data structure and wide-spread availability have made them a popular source for digital terrain modeling and watershed characterization.
The two primary data sets which must be obtained to perform watershed delineation with DEMs are elevations, and flow directions. The most common form of DEM elevations are the USGS digital maps. 1:250000 scale (90 meter resolution).
DEMs can be downloaded free of charge from the EROS home page. Other sources of elevation data may include federal, state, and local government agencies, universities, or private data publishers. WMS can read digital elevation in standard USGS, ARC/INFO/ArcView ASCII grid, and GRASS grid formats. Flow direction data for DEM points must be computed using the flow direction command in ARC/INFO/ArcView, GRASS, or by using the version of TOPAZ especially created for distribution with WMS.
Typical steps for using DEMs to develop hydrologic models.
1. Obtain and Import a Digital Elevation Model (DEM)
2. Import a Flow Direction Grid
3. Compute Flow Accumulations
4. Identify the Watershed Outlet and Convert DEM Streams to Arcs
5. Define Interior Sub-basin Outlet Points
6. Define Basins
7. Convert DEM Basins to Polygons
8. Compute Basin Geometric Data
9. Define the Hydrologic Model
Guidelines for Using TIN Data
The following steps can be used as a guideline for watershed characterization with TINs.
1. Obtain Background Elevation
2. Smooth the Background Elevation
3. Create a Conceptual Model with Feature Objects
4. Redistribute Vertices
5. Create TIN
6. Edit TIN
7. Complete Stream Network and Outlet Definitions
8. Delineate Basins
9. Refine TIN
10. Compute Basin and Stream Parameters
11. Define the Hydrologic Model
Built-In Model Checker
WMS includes a built-in Model Checker. The Model Checker will check over the input data for any modeling errors. If it encounters an error, it will explain what is wrong and how to correct it.
Windows: 386/486/Pentium running Microsoft Windows 3.1/NT/95, math coprocessor and 4 MB RAM.
UNIX X-Windows: AIX, HP-UX, IRIX, OSF, SunOS, SPARC Solaris.
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Τελευταία Ενημέρωση 27 Ιουλίου 2004 - Last Revised on July 27, 2004
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