David R. Maidment

Geographic Information Systems (GIS)-based spatially distributed model for runoff routing

A method is proposed for routing spatially distributed excess precipitation over a watershed to produce runoff at its outlet. The land surface is represented by a (raster) digital elevation model from which the stream network is derived. A routing response function is defined for each digital elevation model cell so that water movement from cell to cell can be convolved to give a response function along a flow path and responses from all cells can be summed to give the outlet hydrograph. An example application of analysis of runoff on Waller Creek in Austin, Texas, is presented.

Climate-change impacts in a regional karst aquifer, Texas, USA

Climate-change scenarios were created from scaling factors derived from several general circulation models to assess the likely impacts of aquifer pumping on the water resources of the Edwards Balcones Fault Zone (BFZ) aquifer, Texas, one of the largest aquifer systems in the United States. Historical climatic time series in periods of extreme water shortage (1947–1959), near-average recharge (1978–1989), and above-average recharge (1975–1990) were scaled to 2 × CO2 conditions to create aquifer recharge scenarios in a warmer climate. Several pumping scenarios were combined with 2 × CO2 climate scenarios to assess the sensitivity of water resources impacts to human-induced stresses on the Edwards BFZ aquifer. The 2 × CO2 climatechange scenarios were linked to surface hydrology and used to drive aquifer dynamics with alternative numerical simulation models calibrated to the Edwards BFZ aquifer. Aquifer simulations indicate that, given the predicted growth and water demand in the Edwards BFZ aquifer region, the aquifer’s ground water resources appear threatened under 2 × CO2 climate scenarios. Our simulations indicate that 2 × CO2 climatic conditions could exacerbate negative impacts and water shortages in the Edwards BFZ aquifer even if pumping does not increase above its present average level. The historical evidence and the results of this article indicate that without proper consideration to variations in aquifer recharge and sound pumping strategies, the water resources of the Edwards BFZ aquifer could be severely impacted under a warmer climate. 2000 Elsevier Science B.V. All rights reserved.

An integrated system for publishing environmental observations data

Over the next decade, it is likely that science and engineering research will produce more scientific data than has been created over the whole of human history. The successful use of these data to achieve new scientific breakthroughs will depend on the ability to access, integrate, and analyze these large datasets. Robust data organization and publication methods are needed within the research community to enable data discovery and scientific analysis by researchers other than those that collected the data. We present a new method for publishing research datasets consisting of point observations that employs a standard observations data model populated using controlled vocabularies for environmental and water resources data along with web services for transmitting data to consumers. We describe how these components have reduced the syntactic and semantic heterogeneity in the data assembled within a national network of environmental observatory test beds and how this data publication system has been used to create a federated network of consistent research data out of a set of geographically decentralized and autonomous test bed databases.

UNIT HYDROGRAPH DERIVED FROM A SPATIALLY DISTRIBUTED VELOCITY FIELD

A unit hydrograph model is proposed in which the watershed is decomposed into subareas which are individual cells or zones of neighbouring cells. The unit hydrograph is found for each subarea and the response at the outlet to excess rainfall on each subarea is summed to produce the watershed runoff hydrograph. The cell to cell flow path to the watershed outlet is determined from a digital elevation model. A constant flow velocity is assigned to each cell and the time lag between subarea input and response at the watershed outlet is found by integrating the flow time along the path from the subarea to the outlet. The response function for a subarea is modelled as a lagged linear reservoir in which the flow time is equal to the sum of a time of translation and an average residence time in the reservoir. It is shown that the assumption of a spatially varying, but time-invariant, velocity field underlying this model produces a linear system model for all subareas whose outputs can be summed in the manner indicated. An example application is presented for the 8.70 km2 Severn watershed at Plynlimon in Wales using a 50 m digital elevation model in which the cell velocity is calculated by modifying an average watershed velocity according to the terrain slope and the drainage area of each cell. The resulting model reasonably reproduces the observed unit hydrograph.

Five‐minute, 1/2°, and 1° data sets of continental watersheds and river networks for use in regional and global hydrologic and climate system modeling studies

A major shortcoming of the land surface component in climate models is the absence of a river transport algorithm. This issue becomes particularly important in fully coupled climate system models (CSMs), where river transport is required to close and realistically represent the global water cycle. The development of a river transport algorithm requires knowledge of watersheds and river networks at a scale that is appropriate for use in CSMs. These data must be derived largely from global digital topographic information. The purpose of this paper is to describe a new data set of watersheds and river networks, which is derived primarily from the TerrainBase 5′ Global DTM (digital terrain model) and the CIA World Data Bank II. These data serve as a base map for routing continental runoff to the appropriate coast and therefore into the appropriate ocean or inland sea. Using this data set, the runoff produced in any grid cell, when coupled with a routing algorithm, can easily be transported to the appropriate water body and distributed across that water body as desired. The data set includes watershed and flow direction information, as well as supporting hydrologic data at 5′, 1/2°, and 1° resolutions globally. It will be useful in fully coupled land-ocean-atmosphere models, in terrestrial ecosystem models, or in stand-alone macroscale hydrologic-modeling studies.

River Network Routing on the NHDPlus Dataset

AbstractThe mapped rivers and streams of the contiguous United States are available in a geographic information system (GIS) dataset called National Hydrography Dataset Plus (NHDPlus). This hydrographic dataset has about 3 million river and water body reaches along with information on how they are connected into networks. The U.S. Geological Survey (USGS) National Water Information System (NWIS) provides streamflow observations at about 20 thousand gauges located on the NHDPlus river network. A river network model called Routing Application for Parallel Computation of Discharge (RAPID) is developed for the NHDPlus river network whose lateral inflow to the river network is calculated by a land surface model. A matrix-based version of the Muskingum method is developed herein, which RAPID uses to calculate flow and volume of water in all reaches of a river network with many thousands of reaches, including at ungauged locations. Gauges situated across river basins (not only at basin outlets) are used to autom...

Using SOA and RIAs for water data discovery and retrieval

The main barriers to make full use of the wealth of available online data is that users are unable to rapidly locate relevant web services and retrieve appropriate data sets from different data repositories as well as efficiently reconcile integration between temporal and geospatial data. To address these issues, this paper focuses on the development of an online Water Data Discovery and Retrieval system (WDDRs) to enhance the capabilities of services discovery, data retrieval, and data visualization. The most significant features of WDDRs prototype are reflected in two aspects. On one hand, a water ontology incorporated with Universal Description, Discovery and Integration (UDDI) based enhanced services catalog offers facilities to alleviate semantic heterogeneity and associate semantic information with the web services discovery and data retrieval process. On the other hand, by embracing the capability within the context of Service Oriented Architectures (SOA) and leveraging the latest protocols of several open web service standards and two popular RIAs (Rich Internet Applications) frameworks including the Microsoft Silverlight and the ESRI ArcGIS API for Silverlight, this system provides an interactive web portal which enables users to one-stop search, access, download and visualize different types of geospatial and observational data in a single environment. With the aim of supporting the study of integrated water environmental assessment, several investigations about water data discovery and retrieval were implemented to demonstrate the feasibility and effectiveness of the WDDRs.

A spatiotemporal data model for river basin-scale hydrologic systems

Despite a long history of synergy, current techniques for integrating Geographic Information System (GIS) software with hydrologic simulation models do not fully utilize the potential of GIS for modeling hydrologic systems. Part of the reason for this is a lack of GIS data models appropriate for representing fluid flow in space and time. Here we address this challenge by proposing a spatiotemporal data model designed specifically for large‐scale river basin systems. The data model builds from core concepts in geographic information science and extends these concepts to accommodate mathematical representations of fluid flow at a regional scale. Space–time is abstracted into three basic objects relevant to hydrologic systems: a control volume, a flux and a flux coupler. A control volume is capable of storing mass, energy or momentum through time, a flux represents the movement of these quantities within space–time and a flux coupler insures conservation of the quantities within an overall system. To demonstrate the data model, a simple case study is presented to show how the data model could be applied to digitally represent a river basin system.

Integrating Arc Hydro Features with a Schematic Network

A framework for integrating GIS features with processing engines to simulate hydrologic behavior is presented. The framework is designed for compatibility with the ArcGIS ModelBuilder environment, and utilizes the data structure provided by the SchemaLink and SchemaNode feature classes from the ArcGIS Hydro data model. SchemaLink and SchemaNode form the links and nodes, respectively, in a schematic network representing the connectivity between hydrologic features pertinent to the movement of surface water in the landscape. A specific processing engine is associated with a given schematic feature, depending on the type of feature the schematic feature represents. Processing engines allow features to behave as individual hydrologic processors in the landscape. The framework allows two types of processes for each feature, a Receive process and a Pass process. Schematic network features operate with four types of values: received values, incremental values, total values, and passed values. The framework assumes that the schematic network is dendritic, and that no backwater effects occur between schematic features. A case study is presented for simulating bacterial loading in Galveston Bay in Texas from point and nonpoint sources. A second case study is presented for simulating rainfall-runoff response and channel routing for the Llano River in Texas.

Hydrology of the Jordan River Basin: A GIS-Based System to Better Guide Water Resources Management and Decision Making

A new method of participatory decision support that can be used in transboundary basins is presented. The framework of this method relies first on the creation of a transboundary geographic information system database to store hydrologic data and allow easy access to data from stakeholders. A participatory hydro-political framework is developed to help set up hydrologic models and evaluate joint water management scenarios. Results show that the countries of the Jordan River could benefit from the framework and in the case of southern Lebanon, six climate stations should be replaced or reactivated. Finally, the mechanism of a Lebanese Hydrologic Information System is presented and shows that an observation data model will facilitate science and policy integration.