In dryland regions, where water is a limited resource, land use/land cover has undergone and continues to undergo significant change mainly due to human activities. The nature of runoff from dryland regions and the influence of land use/land cover change are largely not quantified. The objective of this study is to examine runoff dynamics and the influence of land cover in drylands of western Texas across multiple spatial and temporal scales. The study consists of four major components: (1) an experimental study at Honey Creek upland catchment (19 ha) to assess vegetation treatment effects on runoff by hydrometric and isotopic methods; (2) a hydrochemical evaluation of hydrologic linkage between the upland and bottomland at the second-order Honey Creek watershed; (3) a detailed precipitation-streamflow analysis at North Concho River basin to assess long-term and large-scale precipitation-streamflowvegetation dynamics; and (4) a comparison of streamflow in North, Middle, and South Concho River basins and a regional streamflow trend analysis for the entire western Texas. The study indicates runoff production in the drylands of western Texas is dominated by a few large runoff-producing events. The small catchment experiment indicated that runoff increased about 40 mm per year when 60% of woody plants were removed. This effect may relate to the presence of a baseflow component, but was not verified in regional trend analysis for the Edwards Plateau region where most rivers are spring-fed. The decrease in streamflow in North Concho River basin after the 1950's is in large part related to the enhanced infiltration capacity from reduced grazing pressure and improved vegetation cover. Regional streamflow trend analysis suggests some headwater areas outside the Edwards Plateau region experienced patterns of streamflow change similar to those in North Concho River basin, although artificial impoundments complicated the analysis. The study has broader application in ecohydrological research beyond specific geographic areas and specific vegetation types when evaluating the impact of ecosystem structure change on hydrology and water resources.

Streamflow characteristics change over time as a result of water resources development and management projects, water use, watershed land use changes, and climate changes. The main objective of this thesis is to assess the significance of the impacts of human activities such as construction of reservoirs, water supply diversions, increased water use and return flows on streamflows by the recently completed Texas WAM (Water Availability Modeling) system. The major river basins in the state of Texas were selected as suitable study basins. The particular objective is accomplished by the assessment of WAM monthly and annual naturalized and regulated flows, based on using the WRAP (Water Rights Analysis Package) model, which represents the river/reservoir management model. WAM flow frequency analysis was performed for the simulated flows. The flow ratio indices developed showed the divergence of the actual flows from their natural behavior for the entire monthly flow frequency flow spectrum ranging from minimum flows to high flows. This study describes the combined effects of reservoir construction, increased water use, water resources development projects and land use changes on the river flow regime.

Title from PDF of title page. / Document formatted into pages; contains 75 pages. / Thesis (M.S.C.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Analytical baseflow separation techniques such as those used in the automated hydrograph separation program HYSEP rely on a single input parameter that defines the period of time after which surface runoff ceases and all streamflow is considered baseflow. In HYSEP, this input parameter is solely a function of drainage basin contributing area. This method cannot be applied universally since in most regions the time of surface runoff cessation is a function of a number of different hydrologic and hydrogeologic basin characteristics, not just contributing drainage area. This study demonstrates that streamflow conductivity can be used as a natural tracer that integrates the different hydrologic and hydrogeologic basin characteristics that influence baseflow response. Used as an indicator of baseflow as a component of total flow, streamflow conductivity allows for an empirical approach to hydrograph separation using a simple mass balance algorithm. / ABSTRACT: Although conductivity values for surface-water runoff and ground-water baseflow must be identified to apply this mass balance algorithm, field studies show that assumptions based on streamflow at low flow and high flow conditions are valid for estimating these end member conductivities. The only data required to apply the mass balance algorithm are streamflow conductivity and discharge measurements. Using minimal data requirements, empirical hydrograph separation techniques can be applied that yield reasonable estimates of baseflow. This procedure was performed on data from 10 USGS gaging stations for which reliable, real-time conductivity data are available. Comparison of empirical hydrograph separations using streamflow conductivity data with analytical hydrograph separations demonstrates that uncalibrated, graphical estimation of baseflow can lead to substantial errors in baseflow estimates. / ABSTRACT: Results from empirical separations can be used to calibrate the runoff cessation input parameter used in analytical separation for each gaging station. In general, collection of stream conductivity data at gaging stations is relatively recent, while discharge measurements may extend many decades into the past. Results demonstrate that conductivity data available for a relatively short period of record can be used to calibrate the runoff cessation input parameter used for analytical separation. The calibrated analytical method can then be applied over a much longer period record since discharge data are the only requirement. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

The extent and dynamics of permafrost are tightly linked to the distribution and movement of water in arctic landscapes. As the Arctic warms more rapidly than the global average, profound changes are expected in both permafrost and hydrology; however, much is still not known about the interactions between these two systems. The aim of this thesis is to provide new knowledge on the links between permafrost and hydrology under varying environmental conditions and across different scales. The objectives are to (i) determine how permafrost distributions and patterns in morphology are linked to hydrology, (ii) determine how groundwater flow influences ground temperature dynamics in permafrost landscapes, and (iii) explore the mechanisms that link permafrost to groundwater and streamflow dynamics. A range of methods have been applied within the four studies (papers I-IV) comprising the thesis: geophysical (ground penetrating radar and electrical resistivity tomography) and GIS techniques for mapping and analyzing permafrost distributions and related morphology; numerical modeling of coupled heat and water fluxes for mechanistic understanding permafrost-hydrological links; and statistical analyses for detecting trends in streamflow associated with permafrost thaw. Combining these various methods here allows for, and may be considered a prerequisite for, novel insights to processes. The thesis also presents statistical analyses of field observations of ground temperatures, ground- and surface water levels, as well as lake and shore morphological variables. Discontinuous permafrost peatlands are heterogeneous environments regarding permafrost distributions and thickness which is manifested in surface systems such as lake geometries. In these environments, lateral groundwater fluxes, which are not considered in most permafrost models, can significantly influence ground temperature dynamics, especially during high groundwater gradient conditions. River discharge data provide a potential for monitoring catchment-scale changes in permafrost, as the magnitude and seasonality of groundwater fluxes feeding into streams are affected by the distribution of permafrost. This thesis highlights the need to understand water and permafrost as an integrated system with potential internal feedback processes. For example, permafrost thaw can lead to increases in groundwater discharge which in turn can lead to increased heat transfer through the ground, resulting in further acceleration of permafrost thaw rates. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>

A surge function is a mathematical function of the form f(x)=axpe-bx. We simplify the surge function by holding p constant at 1 and investigate the simplified form as a potential model to represent the full peak of a stream discharge hydrograph. The previously studied Weibull and gamma distributions are included for comparison. We develop an analysis algorithm which produces the best-fit parameters for every peak for each model function, and we process the data with a MATLAB script that uses spectral analysis to filter year-long, 15-minute, stream-discharge data sets. The filtering is necessary to locate the concave-upward inflection points used to separate the data set into its constituent, individual peaks. The Levenberg-Marquardt algorithm is used to iteratively estimate the unknown parameters for each version of the modeled peak by minimizing the sum of squares of residuals. The results allow goodness-of-fit comparisons between the three model functions, as well as a comparison of peaks at the same gage through the year of record. Application of these methods to five rivers from three distinct hydrologic regions shows that the simple surge function is a special case of the gamma distribution, which is known to be useful as a modeling function for a full-peak hydrograph. The study also confirms that the Weibull distribution produces good fits to 15-minute hydrograph data.

Deriving accurate streamflow estimates for ungaged watersheds provides a challenging task for water resource engineers. Traditional methods include correlation to the nearest USGS streamflow station or numeric simulation of watershed rainfall-runoff processes. Mean annual flow, ten percent exceedance and other streamflow indices can be normalized and non-dimensionalized by dividing by the watershed drainage area and the mean annual precipitation rate. Obtaining non-dimensional parameters can be especially useful for extrapolation of flows to downstream, ungaged, coastal fringe regions. Florida and other states along the Gulf Coast exhibit strong variability in the magnitude of streamflow fraction of precipitation. The irregular patterns created by the variance in magnitude do not correlate well with traditional statistical methods of parameter estimation. Using spatial and hydrologic factors, this study, through parameter sensitivity analysis, correlates land-use, slope, soil type, precipitation, and watershed area to a non-dimensional fraction that is to be applied to ungaged regions to determine the streamflow scaling. The study domain for the land-use correlation method is West-Central Florida. Strong trends in correlation to land-use were found but underlying geology must also be considered when defining the study domain. Urbanization, depth-to-water-table and grassland were the dominant parameters in the northern study domain yielding an 80 percent correlation to streamflow fraction for the combined factors. While in the southern domain, wetlands and depth-to-water-table combined to be an indicator with a 75 percent correlation.

The hydrology of the Canadian Prairies has been well described in the scientific literature. 20th C observations show that snowmelt over frozen soils accounted for over 80% of the annual runoff, and streamflow hydrographs peaked in April and ceased in May due to a lack of runoff or groundwater contributions. Since then, the region has undergone rapid changes in land use and climate, both which affect streamflow generating processes. This study evaluates the detailed hydrological impact of regional changes to climate on an instrumented research catchment, the Smith Creek Research Basin (SCRB); an unregulated, wetland and agriculture dominated prairie catchment in south-eastern Saskatchewan. Wetlands have been drained for decades, reducing wetland extent by 58% and maximum storage volume by 79%, and increasing drainage channels lengths by 780%. Long term meteorological records show that there have been gradual changes to the climate: though there are no trends in annual precipitation amount, increasing temperatures since 1942 have brought on a gradual increase in the rainfall fraction of precipitation and an earlier snowmelt by two weeks. In the summer months, the number of multiple day rainfall events has increased by 5 events per year, which may make rainfall-runoff generation mechanisms more efficient. Streamflow records show that annual streamflow volume and runoff ratios have increased 14-fold and 12-fold, respectively since 1975, with major shifts in 1994 and 2010. Streamflow contributions from rainfall-runoff and mixed-runoff regimes increased substantially. Snowmelt runoff declined from 86% of annual discharge volume in the 1970’s to 47% recently while rainfall runoff increased from 7% to 34%. Annual peak discharge tripled over the period from 1975 to 2014, with a major shift in 1994, while the duration of flow doubled in length to 147 days after a changepoint in 1990. Recent flooding in the SCRB has produced abnormally large streamflow volumes, and flooding in June 2012 and 2014 was caused solely by rainfall, something never before recorded at the basin. Although the observed changes in climate and wetland drainage are substantial, it is unlikely that a single change can explain the dramatic shifts in the surface hydrology of the SCRB. Further investigation using process hydrology simulations is needed to help explain the observed regime changes.

General water rights adjudications are now taking place in Arizona. The Gila River and Little Colorado River adjudications are among the largest court proceedings ever undertaken in the United States, involving more than 78,000 water rights claims scattered over 50,000,000 acres of land. The cost of individually proving such a number of individual claims in a formal trial setting would be enormous — often greater than the water's economic worth. Also, the time required to complete such a proceeding would take decades. Consequently, alternative procedures are needed to streamline the investigations and forestall a potentially serious water resource management problem. There are an estimated 22,800 stockwatering ponds (stockponds or stocktanks) in the Gila River Basin alone, and each potentially could be tried as an individual case. If small claims such as those for stockwatering could be considered de minimis in their impact on other higher priority uses, they might be adjudicated as one class of use, thereby fore-stalling a case-by-case trial of each individual water right claim. However, a major obstacle in granting special treatment to small claims lies in demonstrating to litigants that certain small water uses do not, in fact, have a discernible impact on other downstream water right holders. This study was undertaken to quantify the actual losses to a river system from stockwatering ponds, and to compare those losses to other naturally occurring impacts on the hydrologic system. Employing a watershed model, portions of the Walnut Gulch Experimental Watershed at Tombstone, Arizona, an area located within the San Pedro watershed, were analyzed. Storm runoff was simulated with and without the presence of stockponds. Different storm events and storage conditions were modeled in order to measure the impact of stockpond storage under a wide range of field circumstances. This study demonstrated that the hydrologic effects of stockwatering ponds are de minimis with respect to their impact on other water users many tens or hundreds of miles downstream on the river system. Stockpond numbers, capacities, volume/surface area relationships, quantification methods, and effective retention are also evaluated. Statutes in other states are reviewed for their approach to handling stockwatering uses.

Irrigation practices in the Rincon Valley and Mesilla Basin of the Lower Rio Grande have evolved over the last century into a complex setting of transboundary conjunctive use. Three major water users have surface and groundwater appropriation rights regulated by compact, treaty, and operating rules and agreements. The analysis of complex relationships between supply/demand components and the effects of surface-water and groundwater use requires an integrated hydrologic model to track all of the use and movement of water. Models previously developed for the region relied on a priori estimates of net irrigation flux or externally-calculated landscape water budgets. This study instead utilizes a MODFLOW model with the Farm Process (MF-FMP), which directly couples the surface-water and groundwater regimes through simulation of landscape processes. This allows the assessment of stream-aquifer interactions in the context of fulfilling irrigation demands with variable supplies of surface water allotments and supplemental groundwater pumping. MF-FMP also simulates direct uptake of groundwater by crops, an important utility for modeling a region with significant acreage dedicated to pecan orchards, a phreatophytic crop. The abilities and limitations of this new model are explored through scenario simulations meant to estimate streamflow depletions caused by historic pumping levels.

Both natural and anthropogenic climate change are driven by forcings that interact and result in hydroclimatic changes that alter ecosystems and natural resources at different temporal and spatial scales. Accordingly, changes within regions (i.e. individual points to large watersheds) may differ from patterns observed at sub-continental to global scales, thus necessitating the generation of point- to region-specific, cross-scale hydroclimatic data to elucidate important drivers of observed changes, and provide information at scales relevant to resource managers. Herein, we use the Northern U.S. Rocky Mountains as a study region to explore 1) the covariability between observed hydrologic and climatic changes, 2) the nature of changes occurring at the scale of days to decades, and 3) the ocean-atmosphere teleconnections operating at continental- to hemispheric-scales underlying the observed regional patterns of hydroclimatic variability. We then expand the scope of study to include the entire central North American Cordillera to investigate changes in winter precipitation (i.e. snowpack) spanning the last millennia+, with a focus on the spatial and temporal coherence of events from the medieval climatic anomaly to present. To accomplish this we utilize the full suite of hydroclimatic observational records in conjunction with proxy records of snowpack derived from a distributed network of tree-ring chronologies.Results from observational records in the Northern Rockies show important changes have occurred in the frequency and means of biophysically important temperature thresholds, and that recent changes appear greater in magnitude at the mid- to high-elevations. These changes, coupled with interannual- to interdecadal-scale moisture variability driven by ocean-atmosphere teleconnections, are shown to be strong controls on the timing and amount of regional snowpack and streamflow. Across the cordillera, tree-ring based records of snowpack show that before 1950, the region exhibited substantial inter-basin variability in snowpack, even during prolonged droughts and pluvials, marked by a predominant north-south dipole associated with Pacific variability. Snowpack was unusually low in the Northern Rocky Mountains for much of the 20th century and over the entire cordillera since the 1980s; heralding a new era of snowpack declines entrained across all major headwaters in western North America.