Mark Ross

Variability in Specific Yield under Shallow Water Table Conditions

Investigation is provided concerning the variable behavior of specific yield ( SY ) under shallow water table conditions ( <2 m below land surface). Traditionally, specific yield has been defined as the water released from pumping of a phreatic aquifer down by a unit head. It is often used as a fixed value in groundwater flow models. This study seeks to elucidate SY variability due to natural processes of evapotranspiration (ET) and recharge. SY variability is of fundamental importance for modeling hydrologic response from stresses and for determination of water budget of a catchment. HYDRUS 1D—a numerical model solving Richard’s equation for saturated—unsaturated flow in one dimension is used to simulate the behavior of specific yield for a soil type representative of west central Florida. It was found, that for various cases examined (e.g., ET and infiltration), the magnitude of specific yield varied with depth to water table. For infiltration response, the variation in the specific yield exhibited stro...

Fluidization of Soft Estuarine Mud by Waves

The interaction between waves and soft muddy bottoms, a key process in governing estuarine and lacustrine cohesive sediment transport, is at present not well understood. What is quite well known, however, is that waves are significantly important in generating fluid mud, a high concentration near-bed slurry, which thereby becomes potentially available for transport by tidal currents. It follows that the precise mechanism by which fluid mud is formed by wave action over cohesive, porous solid beds is of evident interest in understanding and interpreting the microfabric of flow-deposited fine sediments in shallow waters. Results from preliminary laboratory tests described using known soil mechanical principles shed some light along these lines, and suggest that the fluidization process may be even more significant in generating potentially transportable sediment than previously realized.

A multi-period mixed integer linear programming model for water and energy supply planning in Kuwait.

The demand for water often necessitates desalination, particularly in arid coastal environments. Desalination is often integrated with electrical cogeneration. The demands for water and electricity change over time and are subject to uncertainty. A country-wide large-scale energy and water cogeneration planning model for Kuwait is formulated as a multi-period mixed integer linear programming problem and solved to minimize the net present value over the time period of 2013–2050. Five different plant technology options were considered for desalination and cogeneration including Oil & Multi Stage Flash, Natural Gas & Multi-Effect Distillation, Natural Gas & Reverse Osmosis, Solar Energy & Multi-Effect Distillation, and Solar Energy & Reverse Osmosis. Both water and energy usage in Kuwait and data from existing plants were utilized in providing the parameters and forecasts necessary for solution of the mathematical programming model. The model provides technology choice and associated capacity decisions for existing plants, new plants at green sites, and existing plant capacity expansions as well as their timing to meet the demands.

Discretization approach in integrated Hydrologic Model for surface and groundwater interaction

The commonly used discretization approaches for distributed hydrological models can be broadly categorized into four types, based on the nature of the discrete components: Regular Mesh, Triangular Irregular Networks (TINs), Representative Elementary Watershed (REWs) and Hydrologic Response Units (HRUs). In this paper, a new discretization approach for landforms that have similar hydrologic properties is developed and discussed here for the Integrated Hydrologic Model (IHM), a combining simulation of surface and groundwater processes, accounting for the interaction between the systems. The approach used in the IHM is to disaggregate basin parameters into discrete landforms that have similar hydrologic properties. These landforms may be impervious areas, related areas, areas with high or low clay or organic fractions, areas with significantly different depths-to-water-table, and areas with different types of land cover or different land uses. Incorporating discrete landforms within basins allows significant distributed parameter analysis, but requires an efficient computational structure. The IHM integration represents a new approach interpreting fluxes across the model interface and storages near the interface for transfer to the appropriate model component, accounting for the disparate discretization while rigidly maintaining mass conservation. The discretization approaches employed in IHM will provide some ideas and insights which are helpful to those researchers who have been working on the integrated models for surface-groundwater interaction.

Modeling Evapotranspiration of Two Land Covers Using Integrated Hydrologic Model

Modeling evapotranspiration (ET) distribution in shallow water table environments is of great importance for understanding and reproducing other hydrologic fluxes such as runoff and recharge. Unfortunately, ET distribution can be the most difficult hydrologic process to analyze. The partitioning of ET into upper zone ET, lower zone ET, and groundwater ET is complex because it depends on land cover and subsurface characteristics. One comprehensive distributed parameter model, integrated hydrologic model (IHM), builds on an improved understanding and characterization of ET partitioning between surface storages, vadose zone storage, and saturated groundwater storage. It provides a smooth transition to satisfy ET demand between the vadose zone and the deeper saturated groundwater. In this paper, the IHM was used to analyze ET contribution from different regions of the vadose zone and saturated zone. Rigorous testing was done on two distinct land covers, grass land and forest land, at a study site in West-Cent...

Hydrologic modeling impacts of post-mining land use changes on streamflow of Peace River, Florida

Whether mining activity results in reduced flow of surface water in the Peace River Watershed of Florida has been the subject of much debate. With increased dependence of downstream users on surface water flow of the Peace River as a source of drinking water for four coastal counties in Southwest Florida and problems of water security, the debate has been intensified. It is possible to assess relationships of mining with streamflow in the upper reaches of the Peace River Basin using hydrologic modeling and identify mined sub-basins. In this work, land-use change impacts were simulated by the Hydrological Simulation Program—Fortran (HSPF) model based on geographical information system (GIS) tools, to compare pre- and post-mining streamflows at a study site of the Peace River in west-central Florida. The purpose of this study was to determine if land-use changes caused by mining have negatively impacted streamflow in the Peace River. Changes of land use were identified before and after mining activities. A coupled volume-water depth-discharge (V-h-Q) model based on stage/storage and stage/discharge was applied using HSPF for the pre-mining and post-mining models, respectively. Daily simulated post-mining hydrographs from HSPF were plotted with the calibrated pre-mining results and streamflow hydrographs from the 18 gauging stations, to compare timing of peaks, low flows and flow trends. Analyses of percent exceedances of flow frequency curves of the streams indicated that most streams had similar distributions for mined (reclaimed) and premining periods. In the streamflow change analysis, streamflows actually increased in mining-affected basins at nearly half the stations. Streamflows at other stations diminished. Overall from this comprehensive study, there were declines in streamflow at most gauging stations on the mainstem of the Peace River and its tributaries. The results of this study suggest that regional planning is urgently needed to propose reclamation schemes that enhance regional hydrology.

General Model to Represent Multiple Wetland and Lake Stage-Storage Behavior

Quantifying wetland and lake storage is crucial for developing accurate hydrologic models, especially in regional or large watershed applications with potentially hundreds or thousands of wetlands where detailed survey data are unavailable. This paper evaluates an analytical method that uses a volume-depth ( V-h ) power-function model and a single general shape parameter to predict the storage behavior of multiple wetlands and lakes. This study (1) developed a general shape parameter (i.e., general V-h model) that defines the stage-storage relationships of wetlands and lakes from a diverse and extensive development data set; (2) evaluated the errors associated with storage or stage predictions based on the V-h model; and (3) tested the general V-h model performance on an independent validation data set. The study findings were as follows: (1) General wetland and lake shape parameters were shown to approximately represent stage-storage relationships of each wetland and lake group in this study; (2) the div...

Using Soil Moisture Data to Estimate Evapotranspiration and Development of a Physically Based Root Water Uptake Model

In humid regions such as west-central Florida, evapotranspiration (ET) is estimated to be 70% of precipitation on an average annual basis (Bidlake et al. 1993; Knowles 1996; Sumner 2001). ET is traditionally inferred from values of potential ET (PET) or reference ET (Doorenabos and Pruitt 1977). PET data are more readily available and can be computed from either pan evaporation or from energy budget methods (Penman 1948; Thornthwaite 1948; Monteith 1965; Priestly and Taylor 1972, etc.). The above methodology though simple, suffer from the fact that meteorological data collected in the field for PET are mostly under non-potential conditions, rendering ET estimates as erroneous (Brutsaert 1982; Sumner 2006). Lysimeters can be used to determine ET from mass balance, however, for shallow water table environments, they are found to give erroneous readings due to air entrapment (Fayer and Hillel 1986), as well as fluctuating water table (Yang et al. 2000). Remote sensing techniques such as, satellite-derived feedback model and Surface Energy Balance Algorithm (SEBAL) as reviewed by Kite and Droogers (2000) and remotely sensed Normalized Difference Vegetation Index (NDVI) as used by Mo et al. (2004) are especially useful for large scale studies. However, in the case of highly heterogeneous landscapes , the resolution of ET may become problematic owing to the coarse resolution of the data (Nachabe et al. 2005). The energy budget or eddy correlation methodologies are also limited to computing net ET and cannot resolve ET contribution from different sources. For shallow water table environments, continuous soil moisture measurements and water table estimation have been found to accurately determine ET (Nachabe et al. 2005; Fares and Alva 2000). Past studies, e.g., Robock et al. (2000), Mahmood and Hubbard (2003), and Nachabe et al. (2005), have clearly shown that soil moisture monitoring can be successfully used to determine ET from a hydrologic balance. The approach used herein involves use of soil moisture and water table data measurements. Using point measurement of soil moisture and water table observations from an individual monitoring well ET values can be accurately determined. Additionally, if similar measurements of soil moisture content and water table are available from a set of wells along a flow transect , other components of water budgets and attempts to comprehensively resolve other components of the water budget at the study site. The following section describes a particular configuration of the instruments, development of a methodology, and an example case study where the authors have successfully applied

ESTIMATING EVAPOTRANSPIRATION IN URBAN ENVIRONMENTS

Quantifying evapotranspiration (ET) rates in urban environments is paramount for understanding and modeling other hydrologic fluxes such as runoff and recharge. Large impermeable fractions of land in urban areas may only experience evaporation following rainfall events. Pervious fractions are believed to support most of the ET burden. Point measurements of land-cover ET in pervious areas can provide better estimates of the overall urban ET budget. These can be made by examining changes in the total soil moisture above the seasonal low water table or the ET extinction depth. Soil moisture can be determined by summing the average soil moisture content measured at various depths with capacitance sensors on a vertical probe. Graphs of total soil moisture above the water table for a riparian area in west-central Florida display two distinct slopes, a flattened slope during the overnight period and a steeper slope between approximately 9:00 am and 6:00 pm. The overnight slope is believed to correspond to a process removing moisture continually from the soil, such as gravity drainage. The daylight portion of the slope corresponds to ET plus the continuing downward gravity drainage. Daylight ET is the cause of the difference between the two slopes. Different plant communities exhibit measurably different ET rates and can be estimated using this methodology.

Estimation of Evapotranspiration and Water Budget Components Using Concurrent Soil Moisture and Water Table Monitoring

Simultaneous measurements of soil moisture profiles and water table heads, along a flow path, were used to determine evapotranspiration (ET) along with other components of the water budget. The study was conducted at a small-scale (~0.8 Km2) hydrologic monitoring field site in Hillsborough County, Florida, from January 2002 to June 2004. Frequency Domain Reflectometry soil moisture probes, installed in close proximity to water table monitoring wells were used to derive changes in the soil water storage. A one-dimensional transect model was developed; changes in the soil water storage and water table observations served as input to determine all vertical and lateral boundary fluxes along the shallow water table flow plane. Two distinct land cover environments, grassland and an alluvial wetland forest, were investigated in this particular study. The analysis provided temporally variable ET estimates for the two land covers with annual totals averaging 850 mm for grassland, to 1100 mm for the alluvial wetland forest. Quantitative estimates of other components of a water budget, for example, infiltration, interception capture, total rainfall excess, and runoff were also made on a quarterly and annual basis. Novelty of this approach includes ability to resolve ET components and other water budget fluxes that provide useful parameterization and calibration potential for predictive simulation models.