GIS provides a framework for understanding and managing these complex systems
Ancient civilizations grew up around them, drinking water comes from them, and vacationers flock to themrivers are a crucial but often overlooked part of the freshwater cycle. Reliable sources of freshwater are imperative to the survival of most terrestrial creatures including humans.
According to United Nations Environment Programme, freshwater represents only 2.15 percent of the earth's water. However, the amount of available freshwater is much less because the vast majority of surface freshwater is contained in continental ice.
Rivers, along with lakes, reservoirs, and wetlands, represent the accessible sources of freshwater that support habitats for plant and animal communities and absorb storm water from naturally occurring flooding. For thousands of years, rivers have transported goods and been a source of food. More recently, rivers have been harnesssed for energy production.
Despite their importance, rivers are imperiled by pollution from industry, agriculture, and sewage; compromised by harmful land-use practices; and diverted to meet the demands of a growing and increasingly urban population. Management strategies that employ dams and river course straightening to control the flow, store water, better extract energy, or improve navigation have sometimes been detrimental to habitat and water quality.
The collective result has been degradation that seriously threatens freshwater species. The Second UN World Water Development Report, 2006, reports, "On average, freshwater species populations fell by about 50 percent between 1970 and 2000, representing a sharper decline than measured in either terrestrial or marine biomes."
Government agencies on the federal, state, and local levels, as well as conservation organizations, work to safeguard freshwater systems and depend on GIS for its data management, analysis, and visualization capabilities.
Flow gauge data, bathymetry contours, species population numbers, siltation rates, and pollution levels for various contaminants are a few examples of the many data types required for river management activities. ArcGIS, Esri's comprehensive suite of GIS applications for desktop, server, mobile, and Web platforms, provides a framework for managing and integrating data from many sources in different formats and facilitates data exchange.
ArcGIS allows rivers to be modeled in a variety of ways. Rivers can be represented as a network so that hydrographic flow or ship traffic can be analyzed. A river's areal extent can be portrayed in relation to other types of landforms. A model that describes a river's course and surrounding watershed can be constructed to calculate drainage, descent, flooding potential, and other characteristics.
The development of Arc Hydro, a data model for water resources, has enhanced and standardized data storage and integration. David R. Maidment, director of the Center for Research in Water Resources, University of Texas, Austin, led the consortium that developed Arc Hydro. He has observed, "A river is not just a blue line on a map; it has a complex, three-dimensional morphology that is normally defined using cross sections laid out along the stream centerline." This data model helps handle the complexity of river system data.
Mapping rivers in both two and three dimensions effectively communicates the complex interplay of factors affecting river systems. The visualization capabilities of GIS promote effective communication for decision making within organizations and public concensus building.
In addition to data management and visualization capabilities, ArcGIS supplies tools for analyzing this data. ModelBuilder, part of the geoprocessing framework of ArcGIS Desktop, provides a graphic interface for designing and implementing geoprocessing models that can incorporate tools, data, and scripts. In this visual modeling environment, scenarios can be explored and repeated with a variety of parameters and the processes and data shared with others. When applied to river management, geoprocessing and other analysis tools in ArcGIS are especially useful for watershed modeling, river flow modeling, and land-use inventories.
Many aspects of river preservation involve ongoing monitoring of conditions. Whether determining if drought conditions exist, evaluating habitat remediation efforts, or documenting compliance with federal regulations, monitoring activities can be more effectively carried out using GIS.
An article in this issue describes how Catchment Management Authorities (CMAs) in New South Wales, Australia, have developed a custom ArcGIS extension for measuring biodiversity in each region. With this tool, CMAs can identify existing and potential threats to ecosystems. The extension also assists CMAs in determining and implementing appropriate rehabilitation measures.
A multijurisdictional storm water infrastructure inventory project in Pennsylvania is the subject of another article in this section. The data, gathered using ruggedized Tablet PCs equipped with ArcPad, was shared among upstream and downstream municipalities and with federal and state environmental protection agencies. The project's goals were not only collecting data on sources of particulate matter in area rivers and streams but also inventorying storm water infrastructure. With this information, communities can prioritize retrofit sites and work first on those that will be most beneficial.
A conservation program in western Pennsylvania that is developing a comprehensive river management system for the Allegheny River was hampered by a lack of GIS-ready data at an appropriate scale with sufficient detail. An article in the Focus section details the methods staff members developed for generating that data. Using ArcGIS Desktop with the Spatial Analyst and 3D Analyst extensions and a relatively inexpensive commercial fish finder, the Western Pennsylvania Conservancy generated bathymetry data in-house at a much lower cost than contracting with consultants for that data. This data, combined with river flow data, will allow modeling of pollution concentrations, substrate shifts, and sediment deposition. The completed dataset will benefit many outside the organization from federal agencies to academic researchers and even recreational boaters.
These articles illustrate some of the ways GIS helps gather, analyze, and communicate information about complex river systems vital to the environmental and economic well-being of the communities that surround them. This information can guide decision making and shape a more integrated natural resource management policy that will safeguard rivers.