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Richard M. T. Webb

Publications and source records attributed to Richard M. T. Webb.

10 recordsLinked to original sources
USGS2017

Water, Energy, and Biogeochemical Model (WEBMOD), user’s manual, version 1

The Water, Energy, and Biogeochemical Model (WEBMOD) uses the framework of the U.S. Geological Survey (USGS) Modular Modeling System to simulate fluxes of water and solutes through watersheds. WEBMOD divides watersheds into model response units (MRU) where fluxes and reactions are simulated for the following eight hillslope reservoir types: canopy; snowpack; ponding on impervious surfaces; O-horizon; two reservoirs in the unsaturated zone, which represent preferential flow and matrix flow; and two reservoirs in the saturated zone, which also represent preferential flow and matrix flow. The reservoir representing ponding on impervious surfaces, currently not functional (2016), will be implemented once the model is applied to urban areas. MRUs discharge to one or more stream reservoirs that flow to the outlet of the watershed. Hydrologic fluxes in the watershed are simulated by modules derived from the USGS Precipitation Runoff Modeling System; the National Weather Service Hydro-17 snow model; and a topography-driven hydrologic model (TOPMODEL). Modifications to the standard TOPMODEL include the addition of heterogeneous vertical infiltration rates; irrigation; lateral and vertical preferential flows through the unsaturated zone; pipe flow draining the saturated zone; gains and losses to regional aquifer systems; and the option to simulate baseflow discharge by using an exponential, parabolic, or linear decrease in transmissivity. PHREEQC, an aqueous geochemical model, is incorporated to simulate chemical reactions as waters evaporate, mix, and react within the various reservoirs of the model. The reactions that can be specified for a reservoir include equilibrium reactions among water; minerals; surfaces; exchangers; and kinetic reactions such as kinetic mineral dissolution or precipitation, biologically mediated reactions, and radioactive decay. WEBMOD also simulates variations in the concentrations of the stable isotopes deuterium and oxygen-18 as a result of varying inputs, mixing, and evaporation. This manual describes the WEBMOD input and output files, along with the algorithms and procedures used to simulate the hydrology and water quality in a watershed. Examples are presented that demonstrate hydrologic processes, weathering reactions, and isotopic evolution in an alpine watershed and the effect of irrigation on water flows and salinity in an intensively farmed agricultural area.

Techniques and Methods↗
USGS2009

Identifying Hydrologic Processes in Agricultural Watersheds Using Precipitation-Runoff Models

Understanding the fate and transport of agricultural chemicals applied to agricultural fields will assist in designing the most effective strategies to prevent water-quality impairments. At a watershed scale, the processes controlling the fate and transport of agricultural chemicals are generally understood only conceptually. To examine the applicability of conceptual models to the processes actually occurring, two precipitation-runoff models - the Soil and Water Assessment Tool (SWAT) and the Water, Energy, and Biogeochemical Model (WEBMOD) - were applied in different agricultural settings of the contiguous United States. Each model, through different physical processes, simulated the transport of water to a stream from the surface, the unsaturated zone, and the saturated zone. Models were calibrated for watersheds in Maryland, Indiana, and Nebraska. The calibrated sets of input parameters for each model at each watershed are discussed, and the criteria used to validate the models are explained. The SWAT and WEBMOD model results at each watershed conformed to each other and to the processes identified in each watershed's conceptual hydrology. In Maryland the conceptual understanding of the hydrology indicated groundwater flow was the largest annual source of streamflow; the simulation results for the validation period confirm this. The dominant source of water to the Indiana watershed was thought to be tile drains. Although tile drains were not explicitly simulated in the SWAT model, a large component of streamflow was received from lateral flow, which could be attributed to tile drains. Being able to explicitly account for tile drains, WEBMOD indicated water from tile drains constituted most of the annual streamflow in the Indiana watershed. The Nebraska models indicated annual streamflow was composed primarily of perennial groundwater flow and infiltration-excess runoff, which conformed to the conceptual hydrology developed for that watershed. The hydrologic processes represented in the parameter sets resulting from each model were comparable at individual watersheds, but varied between watersheds. The models were unable to show, however, whether hydrologic processes other than those included in the original conceptual models were major contributors to streamflow. Supplemental simulations of agricultural chemical transport could improve the ability to assess conceptual models.

Scientific Investigations Report↗
USGS1999

Sedimentation survey of Lago Yahuecas, Puerto Rico, March 1997

Sediment is filling Lago Yahuecas, a reservoir built to divert water to Lago Guayo for power generation, at an average rate of 2 percent per year. During March 10 to 13, 1997, the U.S. Geological Survey conducted a bathymetric survey of Lago Yahuecas to determine the amount of sediment deposited and sedimentation rate in the reservoir. Also, reservoir sediments were cored and sampled to determine the dry bulk density. Over the last 41 years, the storage capacity of the reservoir has been reduced by approximately 81 percent from 1.76 million cubic meters in 1956 to 0.33 million cubic meters in 1997. The average annual storage capacity loss to sediment deposition in the reservoir us 34,878 cubic meters per year. The average dry bulk density of the sediment samples was 0.98 gram per cubic centimeter. Based on the contributing drainage area of 45.17 square kilometers, the average sediment yield of the basin was estimated to be 757 megagrams per square kilometer per year.

Lago Yahuecas;Puerto Rico↗
USGS1996

Sedimentation survey of Lago Dos Bocas, Puerto Rico, August 1994

Sedimentation has reduced the storage capacity of Lago Dos Bocas by approximately 43 percent over the last 52 years from 37.5 million cubic meters in 1942 to 21.3 million cubic meters in 1994. If the calculated long term sedimentation rate of 311,000 cubic meters per year remains unchanged, the water-supply storage capacity of the reservoir will be exhausted by the year 2062. Sedimentation in the reservoir has not been uniform. Three tributaries flow into the lake: the Rio Grande de Arecibo, the Rio Caonillas, and the Rio Limon. The Rio Grande de Arecibo has the largest drainage basin and was determined to deliver more sediment to the reservoir than the other two tributaries combined. Only minor amounts of sediment have deposited in the Rio Caonillas branch of the reservoir indicating that Lago Caonillas, located immediately upstream, could be the major sediment repository along the Rio Caonillas tributary. Excluding the Lago Caonillas drainage basin, the long-term sediment yield of the Rio Grande de Arecibo drainage basin is approximately one million kilograms per square kilometer per year.

Lagos Dos Bocas↗