Increasing demand for water supplies in semi-arid regions, such as San Antonio, has sparked an interest in potential recharge management through brush control. Two shallow caves under woody plant cover in northern Bexar County, Texas were chosen as study sites where a detailed water budget would be developed. The Headquarters Cave site measures natural rainfall and cave recharge while the Bunny Hole site is instrumented to measure throughfall, stemflow, surface runoff, and cave recharge. Large scale rainfall simulation was used at Bunny Hole to apply water directly above the cave footprint allowing us to determine how recharge differs between natural and simulated rainfall events. Under natural conditions, Headquarters Cave recharged 15.05% of the annual rainfall while Bunny Hole received 4.28%. Natural canopy throughfall measured 59.96% of the water budget; stemflow accounted for 0.48% and canopy interception was 39.56%; no surface runoff was measured. Rainfall simulations conducted at Bunny Hole resulted in an average of 74.5% throughfall, 5.3% stemflow, 20.2% canopy interception, 2.8% surface runoff, and 6.9% cave recharge; simulation intensities were typically higher than natural event intensities. General water budgets across the Edwards Plateau have concluded that evapotranspiration represents 65% of total annual rainfall while percolation and storage accounts for 30% and the remaining 5% is runoff. These studies have been focused on broad water budget parameters while this study looks at more detailed components. No other study to date has been able to combine throughfall, stemflow, surface runoff, and vertical recharge monitoring to quantify the water budget in the Edwards Plateau; these parameters are instrumental in determining a detailed water budget in juniper rangelands. Results from this study illustrate the significance of all aspects of the water budget and are the first to yield a firm measurement of actual upland recharge.

Phosphorus (P) inputs into water reservoirs are the primary cause for accelerated eutrophication affecting water quality. Attempts are underway to regulate inputs originating from concentrated animal feeding operations (CAFOs). The purpose of this research was to relate runoff dissolved (DP) and total P (TP) losses to site-specific characteristics from plots in CAFOs and compare them to their corresponding risk assessment using the Texas Phosphorus Index (PI). Initial studies showed that soil test P (STP) methods used in Texas by inductively coupled plasma were highly reproducible regardless of manure source or application rate. However, NH4OAc-EDTA extraction efficiency was increased with respect to other methods as soil conditions became less acidic, probably due to dissolution of the greater portion of Ca-bound P resulting in STP values that could be three times greater than those of Mehlich III for the same soil. Surface application of dairy manure to high pH soils were positively correlated to STP at various soil-sampling depths down to 15 cm. First order linear relationships between STP values and DP concentrations in runoff were statistically significant for extraction methods and sampling depths but were different among different soils under neutral to calcareous conditions. Attempts to reproduce this relationship on fields that received periodic applications of manure or effluent with various incubation periods failed, although there was a single highly significant relationship between STP and runoff DP for different soils when soil conditions were acid ( pH<6.5) with various sampling depths. Analyses of NH4OAc-EDTA extractable soil elements showed Mg was significantly correlated to DP concentration across various management and soils, indicating that Mg-bound P is a major component controlling P release into runoff. Use of the Texas PI reflected vegetation type closely, with grass-covered sites averaging the lowest risk rating, and having the lowest DP and TP losses, while conversely tilled sites had the highest. However, overall relationship was poor when estimates for erosion rates were used due to experimental design limitations. Use of measured erosion rates for plots and inclusion of extractable Mg improved correlations between PI rating to DP and TP losses, with r2 ranging from 0.60 to 0.87.

Thesis (Ph. D.)--University of Florida, 2004. / Title from title page of source document. Document formatted into pages; contains 134 pages. Includes vita. Includes bibliographical references.

Thesis (Ph. D.)--University of North Texas, May, 2008. / Title from title page display. Includes bibliographical references.

Thesis (Ph.D.)--Mississippi State University. Department of Plant and Soil Sciences. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xv, 188 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 134-137).

The U.S. Environmental Protection Agency is in the process of developing a nationwide standard for turbidity in construction site runoff. It is widely expected that this standard cannot be met with conventional erosion and sediment control measures; consequently, innovative practices for managing sediment on construction sites must be developed. The objective of this research was to develop an understanding of how soil characteristics and polymer properties affect the amount of turbidity reduction that can be achieved through flocculation. The polymers used were PAMs, a proprietary product, and chitosan. The charge density of the PAMs ranged from 0% to 50% and the molecular weights ranged from 0.2 to 14 Mg/mol. A protocol for creating modified synthetic stormwater runoff for soil samples was developed and used on soils from seven construction sites. Particle size distributions were used to compare the modified synthetic stormwater runoff with grab samples of stormwater from one site and showed the synthetic runoff was representative of the actual runoff. Flocculation tests were performed on the synthetic runoffs with PAM and chitosan doses from 0.03 to 10 mg/L. The non-ionic PAM, proprietary product, and chitosan were found to be the most effective at reducing the turbidity of all the synthetic runoff below 200 NTU. The high molecular weight anionic PAMs were effective on only two of the seven synthetic runoff samples. Hardness tests were performed indicating interparticle bridging to be the bonding mechanism of the PAM. Electrophoretic mobility tests were performed on two of the soil suspensions and indicated the bonding mechanism of PAM to be interparticle bridging, and the bonding mechanism of chitosan to be a combination of charge neutralization and interparticle bridging. Tests showed as the charge density of the PAM increased, their effectiveness decreased. / text

Extended detention basins are not used for stormwater quality management in many areas of the US because they generally do not achieve the 80% removal of total suspended solids required by many regulatory agencies. The objective of this research was modification of the outlet controls of an existing basin to provide batch treatment of the urban stormwater runoff through efficient control of the hydraulic residence time. A solar powered automated valve and controller were developed and placed on the outlet of an extended detention basin in Austin, Texas to increase the detention time beyond the times achievable using an orifice. This system retained the diverted runoff in the basin for a variable preset period of time. The quality of the influent and effluent of the basin was monitored for concentrations of suspended solids, nutrients, chemical oxygen demand. and total and dissolved metals. The suspended solids concentrations in the basin were controlled by adjusting the residence time of the runoff in the basin to meet the required pollutant reduction. The automated valve can also be used to regulate flow into the receiving waters to control peak flow.

Superelevation transition is often used to help balance the centrifugal forces on vehicles through curved roadway sections. Such transitions have regions with near-zero cross-slope as the pavement cross-section rotates from a negative to positive grade. For drainage of roadway surfaces, regions with near-zero slope constitute 'irregular topography'. This condition promotes extended stormwater runoff drainage path lengths and may result in excessive splash from vehicles and hydroplaning. A critical concern is the effect of longitudinal slope on stormwater drainage through superelevation transition. The overall goal of this study is to provide design guidance on longitudinal slope at superelevation transitions through application of a numerical simulation model of highway drainage. Sheet flow on urban pavement surfaces is very shallow, typically measuring a depth less than one centimeter. For modeling of such flow conditions, any small discontinuity or over-simplification of the surface geometry may result in failure in the flow computation. The kinematic wave approximation to the full Saint-Venant equations is often used in many surface and subsurface water models due to its simplicity in application. However, this model fails when backwater effects, ponding, or flow on reverse slope occurs in the local scale. Furthermore, due to the complexity in the surface geometry and the existence of drainage systems, the kinematic wave model is not sufficient for modeling urban stormwater runoff. On the other hand, the full dynamic wave (DW) model usually requires more computational effort. The long computation time of DW model often compromises the accuracy of the model, making the model practically inefficient. In this study, an algorithm was developed to properly represent the irregularly shaped roadway surfaces near superelevation transition areas with unevenly spaced curvilinear grids based on the geometry profile provided by a roadway design software package such as MicroStation CAD. With this accurately defined geometric representation, a nonlinear hydrodynamic diffusion wave model for hydraulic analysis developed in this research estimates the flow depth and runoff volume on the pavement surfaces. The model computes the flow responses for rising hydrographs using a preconditioned general Conjugate Gradient method. Kinematic boundary conditions developed for the open boundaries at the upstream and downstream boundaries compute the boundary values explicitly at each time step. The result of a numerical experiment shows that the spread and concentration of sheet flow is closely related to the transition in cross slope, longitudinal slope, rainfall intensity, and the width of the road. The characteristics of the sheet flow on superelevation transition areas are analyzed to find the optimal longitudinal slope. It is found that the longitudinal slope in the range of 0.3%-0.4% is the optimal slope at superelevation transition areas which minimizes the depth of stormwater runoff. An example application of the model on a rural highway in Texas is also presented. It is found that a significant amount of stormwater may exist on traffic lanes at the superelevation transitions tested. The predicted ponding depth exceeds the minimum value for potential hydroplaning, and the pattern of the flow concentration may cause differential drag forces on traffic vehicles. / text

An Office of Arid Lands Studies Report to the City of Tucson, Real Estate Division, Contract No. 0255-83 / "This report represents one of two parts of the project "Evaluation, Monitoring and Operation of Existing City Water Harvesting System and Expansion Plan for Future Development of Rainfall Utilization," funded by the City of Tucson during the period November 1982 to June 1983." / Introduction: This report deals with the potential harvesting of rainfall and runoff in the Tucson urban area, as distinguished from the rural (farmland) setting that is discussed separately. The principal differences are that 1) rainfall catchment surfaces like rooftops and pavement already exist in the urban area, and 2) harvested rainwater in the urbanized area can be put to a variety of beneficial uses.