Integrated Management of Surface Water and Groundwater – Approaches and Systems Tools

William Yeh

Department of Civil and Environmental Engineering

University of California, Los Angeles, California

Abstract: Increasing demands for water by competing users pose new challenges for water resources managers. Decision makers must understand the interactions between surface water, groundwater and the environmental system. Additionally, the decisions made with regard to water transfer and allocation must take into consideration the diverse objectives that include water supply, cost efficiency and ecosystem protection. This paper reviews the concept of multiobjective optimization, and systems analysis approaches and tolls developed for water resources planning and management with particular emphasis on the linking of simulation models to optimization. This paper will also review the integrated management of surface water and groundwater in Southern California as well as the saltwater intrusion barrier projects in the coastal plain in Southern California.

Understanding the Dynamics of Contaminant Transport near a Salt Wedge using Field/ Laboratory Observations and Computer Simulations

T. Prabhakar Clement

Associate Professor

Auburn University

In this presentation, I will discuss multiple laboratory, field, and computer simulation datasets to illustrate the contaminant transport issues associated with saltwater intrusion dynamics. This is a short summary of the projects completed by the members of my research group in the past five years. The field dataset is based on a two-year field investigation of a dissolved hydrocarbon plume flowing towards a tidally- and seasonally-forced estuarine river system (Westbrook et al. 2005). Installation and sampling of several multi-port wells along the saline riverbank and into the river enabled us to map both vertical and horizontal definition of the hydrocarbon plume. Using the field data, a conceptual model was developed to illustrate the hydrodynamic controls of groundwater and contaminant discharge patterns occurring near a groundwater and saltwater interface.

Our laboratory research focused on developing physical models to study the transient migration patterns of contaminants in unconfined aquifers (e.g., Simpson et al. 2003). Observations were made in laboratory-scale tanks to record the salt-wedge intrusion and recession processes occurring in an unconfined aquifer. Later, the effect of basement heterogeneity on accumulating salts within an unconfined aquifer was studied. The salt accumulation processes due to gradual invasion of saltwater (due to natural reduction in aquifer flow), and the salt accumulation processes due to sudden invasion of saltwater (due to catastrophic events such as tsunami) were studied. Finally, experiments were completed to record the migration patterns of anthropogenic contaminants (such as nutrients and other organic contaminants) released just beneath and above the salt water wedge. These laboratory observations provide data to develop conceptual models for modeling various types of transport problems occurring near a salt wedge.

Our modeling efforts focus on benchmarking density coupled codes using various types of theoretical and experimental datasets (Simpson and Clement, 2003 & 2004). Two classes of benchmark problems that involve stable and unstable internal interfaces and their respective role in testing density coupled codes will be presented. Further, a brief introduction to the current version of the reactive transport code RT3D (Clement et al. 2000) and its use in modeling reactive contaminants will also be provided.

References

1) Clement, T.P., C.D., Johnson, Y. Sun, G.M. Klecka, C. Bartlett, Natural attenuation of chlorinated solvent compounds: Model development and field-scale application, Journal of Contaminant Hydrology, vol.42, p.113-140, 2000.

2) Simpson, M.J., T.P. Clement, and T.A. Gallop, Laboratory and numerical investigation of flow and transport near a seepageface boundary, Ground Water, vol 41(5), p.690-700, 2003.

3) Simpson, M.J., and T.P. Clement, Worthiness of the Henry and Elder problems for validating density-dependent flow models, Advances in Water Resources, vol (26) p. 17-31, 2003.

4) Simpson, M.J., and T.P. Clement, Improving the worthiness of the Henry problem as a benchmark for density-dependent groundwater flow models, Water Resources Research, vol 40 (1), W01504, doi:10.1029/2003WR002199, 2004.

5) Westbrook S.J., J.L. Rayner, G.B. Davis, T.P. Clement, P.L. Bjerg, and S.J. Fisher, Interaction between shallow groundwater, saline surface water and contaminant discharge at a seasonally- and tidally-forced estuarine boundary, Journal of Hydrology, vol (302) p. 255-269, 2005.

Coastal Aquifer chemical mixing: salt-water freshwater stability issues and possible mechanisms for post-tsunami aquifer mixing.

Scott W. Tyler

Professor of Hydrology

Department of Geologic Science and Engineering

University of Nevada, Reno

Reno, NV

tylers@unr.edu

http://equinox.unr.edu/homepage/tylers/

Convective behavior in aquifers and porous media are often overlooked as possible mixing mechanisms of both salinity and contaminants. Vertical or horizontal gradients of fluid density, either from salinity or temperature are quite common in many aquifer systems and can lead to convective fluid motion not easily predicted from water level or peizometric level analysis. The development of convection cells in aquifers is controlled by fluid density contracts, fluid density gradients, and aquifer permeability and the diffusion/dispersion properties of either salinity or heat. System stability can be parameterized through the Rayleigh number, a non-dimensional representation of the ratio of buoyancy forcing to resistive forcing.

Of particular interest to coastal aquifers inundated by tsunami waves may be case of a relatively thin layer of denser seawater infiltrated over a fresher ground water. Such an unstable density contract can lead, depending upon aquifer parameters, to a convective mixing pattern in the aquifer in which the denser seawater descends through the aquifer in plume-like structures. In this lecture, an overview of density driven miscible flows in aquifers will be presented, along with examples of laboratory and field data showing the nature of mixing and stratification that can occur in saline-fresh water aquifer systems. A discussion of the possible application of stability analysis to better understand the salinity distribution in coastal aquifers following the tsunami wave will also be presented.

This discussion will then be followed by an overview of UNR student/faculty international activities in the area of public water supply. To date, UNR students and faculty have led 7 work trips, primarily to developing countries, to transfer technology on drinking water and water resource management and also to provide volunteer labor and training to local water managers. These work trips are completely volunteer driven and funded by local donations, yet provide a tremendously valuable educational experience for American students to learn about other cultures, while also providing a valuable service to the host country. Work trips have included drilling water wells in Kenya, repairing and training Haitian teams to repair village hand pumps in drilled and dug wells, sanitation and water resource education in Panama and measurement of evapotranspiration in Chilean wetlands. It is hoped that through these discussions, appropriate projects for UNR and other US university students can be developed or expanded in Sri Lanka.

Water and Salinity Dynamics in Soils and Groundwater

Rien van Genuchten

George E. Brown, Jr. Salinity Laboratory, USDA, ARS

Riverside, CA

Many of the tsunami-related problems in coastal regions of Sri Lanka involve the salinity of the invading seawater and its effect on local soil and groundwater resources, including agricultural operations. The Salinity Laboratory of the USDA-Agricultural Research Service has a long history of research dealing with water flow and salinity dynamics in the subsurface, especially as related to the unsaturated zone. This presentation reviews some of our basic and applied research that may have direct relevance to the Tsunami-related salinity problems in Sri Lanka. This includes development of user-friendly models for predicting one-and multi-dimensional water and solute transport in soils and groundwater, multicomponent geochemistry, salinity dynamics in irrigated areas, unsaturated soil hydraulic property characterization, the effects of salinity on the soil hydraulic properties, root water uptake and plant salt tolerance, bacteria and virus transport, and instrumental techniques. Some of the modeling tools developed at the Salinity Laboratory (such as especially the HYDRUS and STANMOD codes;

http://www.ussl.ars.usda.gov/models/modelsmenu.htm) should be useful for estimating the general or site-specific effects of salinity (both short- and long-term) on soil and groundwater resources, and for evaluating possible remediation strategies.

Hydrological characterization of the unsaturated zone using cross-borehole radar and resistivity imaging

Karsten H. Jensen

University of Copenhagen

Subsurface heterogeneity complicates a proper field characterization of flow and transport properties using traditional using conventional sampling and monitoring techniques. Data obtained at point locations and in wells may not allow for an accurate representation of subsurface characteristics particularly in the horizontal direction. Recent developments within hydrogeophysics have demonstrated that many hydrogeological studies may benefit from the additional information that cross-borehole electrical resistivity tomography (ERT) and transmission radar tomography can provide. Data on changes in water content and salt concentration can be obtained with an attractive spatial resolution and at a spatial scale suitable for testing and calibrating hydrological models for flow and transport. Such data may underpin predictions of future salinity changes of Tsunami affected soil.

Results will be shown from a site in Denmark located on 20 m unsaturated sandy soil. Two identical field sites have been established each having four ERT and four georadar boreholes. The boreholes are drilled to form a cross consisting of two lines. The two sites are located 8.5 m apart enabling an evaluation of the spatial variability. One of the sites is exposed to natural rainfall and evapotranspiration conditions while at the other one the upper boundary is controlled by irrigation. At both sites tracer in the form of chloride has been added for characterization of transport and dispersion properties. Using resistivity and georadar tomography in combination it is possible to obtain data for the spacio-temporal variations of both water content and tracer concentration. The data will also serve the purpose of estimation large-scale hydraulic parameters for unsaturated flow.

Hydrogeologic and borehole and surface geophysical methods applied to aquifer characterization and water-supply recovery: post-tsunami coastal aquifers, Sri Lanka

Kevin J. Cunningham

U.S. Geological Survey, 3110 SW 9^th Avenue, Fort Lauderdale, Florida 33315, USA

The December 26^th, 2004, tsunami had a huge impact on fresh ground-water supplies in affected areas due to the rapid degradation of the water quality that resulted from overland saltwater flooding of coastal areas. Important to evaluation of the aquifers and restoration of freshwater supplies will be (1) a reliable characterization of the physical system that composes the coastal aquifers, and (2) numerical hydrologic simulation of the tsunami event and the eventual recovery of the coastal aquifers to normal conditions. Assessment of the geologic, hydrologic, and hydraulic parameters of the aquifer are fundamental information needs for aquifer characterization and revitalization of water-supply needs. Hydrogeologic and geophysical methods are the principal tools in accomplishing this assessment. Characterization of the physical system is also a critical component of numerical hydrologic simulations, which are most reliable using an accurate aquifer framework and description of aquifer ground water.

The U.S. Geological Survey’s (USGS) Office of Ground Water—Branch of Geophysics in Storrs, Connecticut, and Center for Water and Restoration Studies in Fort Lauderdale, Florida, have numerous borehole and surface geophysical tools that have relevance to coastal aquifer characterization in Sri Lanka. Specific USGS borehole geophysical tools that could provide important aquifer data include: acoustic televiewer, three-arm caliper, digital borehole imager, electromagnetic induction, flowmeters (heat-pulse, electromagnetic, and spinner), fluid resistivity, fluid temperature, natural gamma ray, spectral gamma ray, single-point resistivity, spontaneous potential, video camera, and borehole water sampler. In addition, surface geophysical instrumentation from the USGS that could produce significant information about the coastal aquifers include: electromagnetic and transient electromagnetic ground conductivity meters, ground-penetrating radar, water-borne continuous resistivity profiling, water-borne seismic reflection profiling, and helicopter electromagnetic surveys. Principal applications of both borehole and surface geophysical methods include: (1) depth to freshwater-saltwater interface(s); (2) measurement of vertical ground-water salinity profiles; (3) determination of depth to bedrock; (4) detection, measurement, and orientation of bedrock fractures; (5) delineation of lithology; (6) mapping of clay (confining) units; (7) detection of porous hydrogeologic units; (8) detection of ground-water flow units or productive fractures; and (9) development of a hydrogeologic framework. Many of these geophysical tools have been practical in characterization of the coastal karst limestone Biscayne aquifer of southern Florida and other aquifers of the United States. Examples of their application will be presented.

Suggested for the characterization of the coastal aquifers and recovery of water supplies in Sri Lanka is a plausible, highly generalized plan for implementation of the use of selected hydrogeologic and geophysical methods. The first step would include drilling monitoring wells and water-supply wells. Geologic core samples recovered from the drilling wells would provide definition of the lithologic composition and hydraulic character of aquifers. Borehole geophysical logs acquired in these wells would produce important information on water-table levels, ground-water salinity, aquifer productivity, and aquifer framework; thus, providing data to map potentiometric surfaces, ground-water quality, trends in productivity, and hydrogeologic framework. These maps could show the location of prospective new water-supply wells for the immediate needs of the impacted population. Geologic contacts, water-table elevations, ground-water salinities, freshwater-saltwater interfaces, and aquifer frameworks would delineate between wells with surface geophysical tools. Hydrogeologic and borehole and surface geophysical data would integrate into conceptual hydrogeologic models that would be functional in numerical hydrologic simulations.

Ground Water Quality Management Through Risk-Based Decision Analysis

Jagath Kaluarachchi

Professor

Civil and Environmental Engineering

Utah State University

Logan, Utah

Management of watersheds with contaminated ground water is becoming a challenging issue in many parts of the world. Since ground water provides the majority of water in rural and urban communities of the world, ground water quality has become an equally priority issue as water quantity. Rural and semi-urban watersheds are prone to ground water contamination due to non-point sources commonly present in various land use and land use practices. A good example is chemicals used in various agricultural activities to increase crop yield. In a detailed ground water quality management project conducted in the Whatcom County, Washington State by Utah State University demonstrated that excessive nitrate buildup in ground water due to large-scale use of nitrogen-rich chemicals in agriculture can be properly modeled and managed using a risk-based management strategy. In this work, the researchers addressed various best management practices to minimize nitrate contamination considering risks and economic benefits. In this presentation, the methodology and the results of the analysis will be presented and discussed.

Due to the recent tsunami in the south Asian region, ground water quality has been compromised due to the unstable regions salinity formed beneath the land surface. Once adequate field data are collected and conceptual models of the physical systems are developed, a methodology similar to the one discussed here can be applied to evaluate the most cost-efficient and timely actions needed to reverse ground water quality to its native conditions.

The 2004 Indian Ocean Tsunami: A Perspective from Natural Hazards to Water Resources

David Hyndman

Department of Geological Sciences

Michigan State University, East Lansing, MI 48854, USA

hyndman@msu.edu

http://www.geology.msu.edu/hyndman_d.html

The consequences of the December 2004 Tsunami were truly catastrophic. Large populations from Sumatra, to Thailand and Sri Lanka live and work very close to sea level and were provided little to no warning of the massive incoming waves. This tragedy illustrated a clear need for both improved warning systems across the Indian Ocean and education to local populations and government officials about future hazardous events and evacuation plans.

In addition to the catastrophic loss of life and property during the tsunami, the waves have also had long-term impacts on local water supplies due to contamination of local wells and infiltration of saline waters. Geophysical techniques such as Ground Penetrating Radar (GPR) can be used to map the extent and thickness of tsunami sands deposited during this and potentially previous events, and to evaluate the saline intrusion into the fresh groundwater system. GPR surveys from the surface can be performed to rapidly map the region, and cross borehole radar tomography can provide more detailed information in areas of interest where multiple boreholes exist of can be drilled. Geophysical information can be coupled with flow and transport models to evaluate changes in water quality since the tsunami, and predict recovery of such supplies. Research into the nature of water supply contamination and the its return to a useable state will provide information that can help design future water supplies in a manner that they will be less likely to be impacted by future tsunami.