Transport phenomena in hydrologic systems are simulated with finite-state models (FSMs), which are similar to mixing cell models in that they utilize a mixing cell as their basic subdivision, yet are more flexible, capable of modeling more complex systems, and easier to manipulate than previous mixing cell models. The basic FSM equations are discrete, recursive forms of the continuity equation for mass transport and the storage equation for fluid transport. Different types of mixing and flow can be simulated by specifying appropriate algorithms for use in the basic equations. Finite-state models thus have a physical basis, although they avoid the use of differential equations. The FSM digital computer model can simulate systems in one, two, or three spatial dimensions with relative facility. In many important cases, transit number and age number distributions can be calculated. These distributions, and especially their means, are useful in determining fluid residence times in hydrologic systems. Two aquifer systems are modeled using finite-state models. In a portion of the Tucson Basin Aquifer of southern Arizona a three-dimensional, steady flow FSM is used to account for the observed carbon-14 age distribution in the aquifer without assuming piston flow in the aquifer and without evaluating dispersion parameters. This model provides a first approximation of the three-dimensional flow distribution, an estimate of the long-term average annual recharge, and fluid residence times in the aquifer. The second FSM, two-dimensional and non-steady flow, accounts for the transient distribution of tritium in the Edwards Limestone of south-central Texas. This aquifer is a highly anisotropic, nonhomogeneous karst aquifer that is difficult to model by traditional methods. In both models, first guesses for cell volumes and flow distributions were made on the basis of available hydrogeological data. Saturated, unsaturated, and open-channel flow also are examined. Flow algorithms for the basic FSM storage equation follow the theory of linear systems, although in certain regimes, especially those involving unsaturated flow, it may be necessary to develop nonlinear flow algorithms. This was not attempted. It is also shown that the finite-state model can simultaneously model the transport of mass and fluid in a hydrologic system. The FSM also has the potential for modeling heat transport, which may prove useful in simulating geothermal reservoirs as well as other systems involving heat transport.

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<p> Streams in the Kenai River watershed are characterized by a fish-rich environment, with competing interests between commercial industry and recreational users. Resource managers strive to balance the needs of both these user groups while maintaining the sustainability of the resource. The ability to estimate future river conditions could help maintain the resource, and a strong, sustainable economy on the Kenai Peninsula. </p><p> This research used the Army Corps of Engineers Hydrological Modeling System (HMS), which transforms rainfall to river discharge. The main goal was to define a set of parameters that were calibrated using an event based strategy, and concurrent rainfall and discharge data. The model was calibrated and validated in three sub-basins located in different environmental settings (i.e. lowlands, mid, and high elevation). In addition, the Kenai River watershed, as a whole, was modeled. </p><p> Due to limited concurrent datasets, a combination of current and historic rainfall and discharge data was used in the calibration. Over the period of time between the historic data and the current data, no major changes in the watershed were detected. </p><p> Model results at the sub-basin and watershed scale provided reasonable results over the modeling period. Each sub-basin maintained errors below 10% for the calibration and only slight increase in the error for the verification trials. It was found that during an extreme precipitation event, the model did not perform within reasonable bounds.</p>

<p> Hydrogeologically, Rapa Nui (Easter Island, Chile) is one of the least understood islands in Polynesia. There are no surface streams, the soils are poor in productivity and highly permeable, and the water table sits far below the surface of the island. One of the many mysteries of Rapa Nui is how the ancient inhabitants survived with so few sources of freshwater. </p><p> Fieldwork was conducted to identify terrestrial sources of freshwater and to evaluate the occurrence of submarine groundwater discharge (SGD). We documented observable surface water features located in the interior and coast of the island and made field measurements of water temperature and salinity to identify areas of SGD along the coast. The limited number of interior surface water features, periods of drought, permeable aquifers, and existence of <i> puna</i> (dug wells) along the coast of Rapa Nui lead us to conclude that coastal seeps were an important prehistoric source of freshwater.</p>

This thesis seeks to extend the work of Thornes and Scoging on hillslope processes in south east Spain by paying particular attention to the relative roles of surface and sub-surface water movement in gully head change on two contrasting soil types. Gully growth is a major agent of erosion in semi-arid environments, yet studies to date have assumed the dominance of surface wash, and only speculated on the role of subsurface water movement. The sampling design was based on the hillslope hydrological cycle and incorporates measures of precipitation, infiltration, and runoff and subsurface flow on catchment areas above gully heads. Additional data on vegetation and some soil properties were collected. The field work was undertaken on three occasions in the summer, autumn and spring of 1982/3 to examine seasonal variations. The analysis of surface flow was hindered by the drought which meant there were only 10 rain days in 1982, and only one storm occurred during the field sessions on 26 November 1982. Despite this several observations can be made. Wash volumes were twice as high on the marl on 26 November. Both lithologies are susceptible to relatively high erosion rates by surface wash although rates tend to be higher on the marl, and there is considerable variation on both lithologies. However for neither lithology is the amount of sediment transported sufficient to fill in the gullies in the medium term. The analysis of the subsurface hydrology shows that saturated conditions were not monitored anywhere, and maximum soil moisture values reached between 50--60% saturation on the marl and conglomerate soils. There are marked seasonal variations in soil moisture and most of the variation occurs in the upper horizons. Flux rates are negligble on the marl and dominantly in the vertical plane. On the conglomerate rates are much faster, and throughflow may well occur on occasions, and at rates exceeding e'apotranspiration. This will contribute to wetter conditions around and in gullies on the conglomerate.

<p> In Louisiana, human actions, such as levee construction for flood protection, have disrupted the connectivity between many rivers and their surrounding wetlands, leading to marsh degradation and land loss. River sediment diversions from the Mississippi River into adjacent wetlands are currently proposed as a large-scale wetland restoration technique. The reintroduction of sediment-rich waters into adjacent wetlands will also come with altered hydrology and nutrient loads. Despite hydrology and nutrient loading being central to many previous studies, many uncertainties remain regarding the marsh response to this type of large-scale environmental alteration. </p><p> To better understand the effect of river sediment diversion related increases in nutrient supply and altered hydrology on tidal freshwater marsh species specific responses and soil physico-chemical properties, we conducted a greenhouse experiment consisting of three common tidal freshwater and brackish marsh species (<i>Panicum hemitomon, Sagittaria lancifolia</i>, and <i> Spartina patens</i>). To mimic diversion specific conditions, we tested high and low nitrate loading rates (35 g N m² y^&ndash;1 and 0.25 g N m² y^&ndash;1, respectively) and two hydrologic regimes to compare diversion and non-diversion. Units were also set at two different soil surface elevations within each treatment, to simulate healthy and degraded marsh types. </p><p> Growth responses measured throughout the study differed between species, but were not influenced by the treatments. After 3 months, aboveground and belowground biomass was not impacted by the treatment for any of the species. Soil redox potential was influenced by changes in hydrology but recovered to pre-study conditions by harvest. This study provides an insight into how proposed river diversion conditions and subsequent recovery may influence the productivity of freshwater marshes. We also further highlight the need for a more complete understanding of how changes in flooding depth, duration, and nitrate load from proposed river sediment diversions will influence the productivity of marshes in receiving basins.</p><p>

<p> Managed Aquifer Recharge (MAR) systems have become an increasingly important approach to the management of groundwater in Southern California in recent years. This thesis describes an experimental investigation of the vadose zone dynamics beneath a recharge basin used by the Orange County Water District. Soil moisture probes, pressure transducers, and fiber optic distributed temperature sensing (FODTS) at multiple depths beneath the basin were used to monitor infiltration. The purpose was to measure the diurnal temperature flux using heat as a tracer of infiltrating water to gain insight on the influence of basin stage (i.e., water level) on infiltration rate. To increase the temperature resolution from the standard 1 m, we installed a wrapped fiber optic cable at two locations using direct push technology. The wrapped FODTS cable was spliced to a trenched cable that ran laterally across the basin at depths of 30 cm and 1 m, installed during a previous experiment. The wrapped cable was then installed vertically at two locations to observe both the spatial distribution and vertical dynamics of fluid flow at 10 cm intervals. Propagation of the diurnal heat flux at the surface was related to water velocity. The infiltration behavior was affected by subtle changes in stratigraphy below the basin. The heat tracer suggests strong components of horizontal flow due to the presence of thin fine-grained hydrostratigraphic units. Water movement during initial saturation was particularly complex and suggested that simple one-dimensional vertical flow models will not accurately predict infiltration rates. The FODTS system provided high-resolution dynamic imaging of percolation that is not possible using a multi-level transducer system.</p><p>

<p> The purpose of this study was to investigate multiple methods used to locate and identify sources of submarine groundwater discharge (SGD) along the coastline of Santa Catalina Island (Catalina) in Los Angeles, California. The driving hypothesis is that SGD may be identified by higher temperature/lower salinity plumes. To test this hypothesis, temperature and conductivity measurements were made along the shoreline of Catalina and compared with previously collected airborne thermal infrared images. In some locations where potential zones of SGD were identified, samples were collected from the surface water within the plume and analyzed for the presence of radon. Radon in ocean water can be used as a tracer to identify the presence of terrestrial groundwater. The analysis was complicated by dynamic variables including tides, weather, and sample collection. In spite of this uncertainty, one potential zone of SGD was identified using sea surface temperature, electrical conductivity, and radon at Toyon Bay. This zone of SGD is consistent with the location of warm water shown in airborne infrared imagery. These results suggest that high-resolution thermal imagery may be useful for identifying diffuse SGD in southern California, but further field tests will be necessary to confirm this conclusion.</p><p>

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