The Ythan River in Grampian Region, Scotland, is being investigated under a European Council Directive (91/676/EEC) for designation as a Nitrate Vulnerable Zone because of an increase in estuarine eutrophication in recent years. This paper explores the use of the GRID module of ArcInfo GIS for hydrological modelling of the River Ythan as part of the development of a spatial decision support system for the river catchment. A topographically correct elevation grid was created for the catchment area using a DEM and digitised stream network. From this, the flow directions, flow accumulations at the pour points, and subcatchment boundaries were created. These were compared with water discharge values measured at the pour points and hand-delineated subcatchment boundaries provided by the North-east River Purification Board. GRID was then used to measure the length of the stream channels, and by assigning suitable water flow velocities, an isochrone map was produced to show the spatial pattern of catchment hydrological response. Currently this hydrological model is being extended to incorporate spatial variation in rainfall and evapotranspiration. The hydrological model is also being coupled with a hydrochemical model to predict the chemical composition of drainage water in the catchment. This will help policy makers decide on suitable methods for reducing nitrate concentrations in the River Ythan and provide a GIS-based framework for modelling hydrochemical responses to altered land use in the catchment.
Flooding is a natural and variable phenomena, it can occur on any land surface, ranging from a street intersection, a home lot to the extensive rural flood plain areas inundated by large rivers such as the Mississippi-Missouri rivers. Flooding results in damage to property, crops and negative impacts on human welfare. Flood Plain Management aims to minimize damages and reduce the threat to human life and welfare when major flood events occurs. Along with these more traditional tasks of river engineers and flood defense managers comes also the requirements of developing solutions which not only meets the design requirements also are friendly to and enhance the environment. Application of the hydraulic numerical modelling tool MIKE 11, developed by the Danish Hydraulic Institute, for flood analysis and flood plain management is a strategic and essential tool for an integrated Flood Plain Management approach, using "Decision Support System" (DSS) technology. Incorporating MIKE 11's capabilities in a DSS allow for analysis of the full impacts on for example flood extents, flood depths, flood damage of present or future options, i.e. "WHAT IF" scenarios can be modelled accurately and confidently. The modeller can at all stages of the integrated process present results to decision makers in a clear and easily understandable formats. Linking the MIKE 11 hydraulic model with GIS (ArcView) merges MIKE 11 and GIS technologies within a DSS Framework. The MIKE 11-GIS interface allows for presentation of flood inundation maps, flood impact maps and related statistics. The maps illustrates the results from a MIKE 11 simulation in a easily assimilated and highly visual format, highly facilitating interpretation and analysis of potential impacts. Several flood maps can be merged into a video, which animates to an example the development of flood inundation during a flood event. The outputs are high quality presentations which are readily suited to Environmental Impact Assessments, Flood Risk Analyses, Flood Damage and Disaster Assessments. The MIKE 11 - GIS interface also allows for extraction of flood plain topography from the Digital Elevation Model (DEM). The flood plain topography is essential for developing accurate and physically correct MIKE 11 applications. The proposed paper presents the concept and case studies of application of MIKE 11 and GIS for integrated Flood Plain and Disaster Management.
Identification of transport and navigational path centerlines through surface-water bodies in geographic information system (GIS) digital-data sets is required for flow modeling and analyses of interconnected streams and lakes. The U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency (EPA), developed an ARC Macro Language (AML) computer program that creates transport-path centerlines through interconnecting lakes and mainstem rivers in the EPA River-Reach File 3 (RF3). This program uses the GRID raster-modeling software, which is a sub-system of the ArcInfo (1.) GIS from Environmental Science Research Institute (Esri). GRID software provides functions to perform least-cost path analyses through raster-data sets by establishing a cost surface, eliminating areas from analyses, and creating barriers in the cost surface. Also, ArcInfo software was used to prepare data for input into GRID, and refine the output for later processing or analysis. 1. The use of product or firm names is for identification purposes only and does not imply endorsement by the U.S. Geological Survey.
The Engineering Computer Graphics Laboratory (ECGL) of Brigham Young University in cooperation with the U.S. Army Engineer Waterways Experiment Station (WES) in Vicksburg, Mississippi has developed a suite of applications for environmental, hydraulic, and hydrologic simulation. These applications include the Dept. of Defense Groundwater Modeling System (GMS), the Surface water Modeling System (SMS), and the Watershed Modeling System (WMS). All three systems include a set of modeling codes along with extensive grid and mesh generation utilities and sophisticated post-processing and visualization tools in both two and three dimensions. The vast majority of modeling codes are based on either the finite difference or finite element approach. Traditionally, most programs designed for pre-processing of these types of models require the user to construct a computational grid that encompasses the problem domain. The user then selects nodes or cells in the grid to assign model parameters such as boundary conditions and material properties. The problem with this approach is that is often requires extensive effort to enter the data and if significant modification is required, the data entry process must be repeated. In light of the limitations inherent in traditional pre-processing applications, the ECGL and WES have developed a new approach within GMS, SMS, and WMS for model development and pre-processing. With the new approach, a high-level representation of the model is constructed using an ArcInfo data model consisting of points, nodes, arcs, and polygons. Model parameters are assigned directly to the GIS entities as attributes. For example, lakes are represented as polygons, rivers are represented as arcs, wells are represented as points, etc. This model is constructed entirely independently of the numerical grid and is referred to as a "conceptual model". Once the conceptual model is developed, a mesh or grid is automatically constructed to fit the conceptual model and all of the model parameters are automatically assigned to the proper cells or elements. The advantage of the conceptual model approach is that it greatly simplifies model creation and if the user modifies the conceptual model, a new computational model can be constructed in seconds. Since the data model utilized in GMS, WMS, and SMS is patterned after the ArcInfo data model, conceptual models and attributes can be shared freely between the three applications and ArcInfo or ArcView.