Thesis (M. P. A.)--Texas State University-San Marcos, 2007. / "Fall 2007." Includes bibliographical references (leaves 62-67).

Thesis (M. P. A.)--Texas State University-San Marcos, 2006. / "Fall 2006." Includes bibliographical references (leaves 54-56).

Cretaceous limestone, marl, and dolomite of Late Aptian to Middle Albian age crop out in the Wimberley area, a 5-minute by 10-minute quadrangle in central Texas situated in the dissected eastern margin of the Edwards Plateau. Formations exposed are the upper part of the Glen Rose, the Walnut, and the lower part of the Edwards. The Glen Rose, which crops out over 90% of the area, is subdivided into 7 informal members defined on mappability on aerial photographs. Six major step faults of the Balcones fault zone transect the area, displacing the strata downward to the southeast about 700 feet. The outstanding geomorphic features are the high relief hills and ridges south of the Blanco River, which are caused by dissection along the Edwards Plateau margin, and the deflections of Cypress Creek and Blanco River where they cross faults. / text

The Signal Hill Quadrangle is located astride the Balcones Escarpment southwest of Austin. Cretaceous rocks (Albian and Cenomanian) cropping out in the area include the upper two members of the Glen Rose Formation, the Bull Creek and Bee Cave Members of the Walnut Formation, the Kainer and Person Formations of the Edwards Group, and the Georgetown, Del Rio, and Buda Formations. Deposition represented by these formations ranges from supertidal to tidal-flat to open-shelf marine environments. At one location there is a basalt plug, probably of Senonian age. The youngest deposits in the quadrangle are those associated with Quaternary terraces and alluvial sands and gravels. The faults mapped are part of the Balcones Fault Zone, a system of en echelon, northeast-trending, predominantly normal, dip-slip faults. This system was probably active in the middle Tertiary. The Mt. Bonnell Fault is the most important fault in the quadrangle. It is one of the major faults of the Balcones Fault System, having been downthrown 170-350 feet to the southeast. The total displacement of all faulting in the map area is about 800 feet. / text

Thesis (M.S.)--Texas State University-San Marcos, 2008. / Vita. Includes bibliographical references (leaves 22-25). Also available on microfilm.

The Leona aquifer is an important, but overlooked, water resource in Central Texas. The Quaternary Leona Formation occurs as several isolated alluvial deposits at the margins of the Edwards Plateau. Each of these deposits forms an aquifer. One of these aquifers is located near Lockhart, Texas. This aquifer is recharged by infiltration of precipitation and is discharged by numerous springs and seeps. Additional sources of discharge are evapotranspiration and cross-formational flow into the Wilcox aquifer. The saturated thickness at this location varies seasonally but is rarely greater than 3 m (10 ft). Groundwater flow in an aquifer of this scale is influenced by its heterogeneous nature. This research identified seven different facies in the Leona Formation and the underlying Wilcox Group. These divisions were based on sediment classification, lithology, and sedimentary structures. The Leona Formation is covered by sandy and silty clay soil and caliche. Each of these facies has different hydraulic properties. Many empirical relationships between grain size distribution and hydraulic conductivity (K) have been discussed in the literature. Equations developed by Hazen, Slichter, Terzaghi, Beyer, Saurbrei, and Kozeny were used to estimate hydraulic conductivity. Hydraulic conductivity was also measured in the laboratory with constant and falling head permeameters. Hydraulic conductivity of the Leona aquifer varies seven orders of magnitude. Hydraulic conductivity varies up to four orders of magnitude within a single facies due to small-scale differences in grain size distribution and degree of cementation. The arithmetic mean of hydraulic conductivity in vertical profiles through the Leona aquifer ranges from 0.013 cm/sec (37 ft/day) to 0.14 cm/sec (397 ft/day). Water quality is a concern for many unconfined shallow alluvial aquifers, including the Leona aquifer. Elevated nitrate levels indicate contamination resulting from agricultural land use. Nitrate concentration in the Leona aquifer ranges from 4 ppm nitrate as NO₃ to greater than 70 ppm nitrate as NO₃. These concentrations are significantly greater than those observed in the Wilcox aquifer. The U.S. Geologic Survey computer code MODFLOW was used to create a groundwater model of the Leona aquifer. In the best simulation, specific yield was 0.1 and horizontal hydraulic conductivity was 0.058 cm/sec (164 ft/day). The simulated hydraulic conductivity is an order of magnitude less than observed in gravel pit outcrops. Modeled recharge was 9 percent of annual precipitation in 2003 and 20 percent of precipitation in the first six months of 2004. Five hypothetical wells were placed in the model to examine the effects of pumping on the aquifer. Wells pumped for 61 days at 0.04 l/sec (0.6 gpm) cause insignificant drawdown while wells pumped at a rate of 3.5 l/sec (55 gpm) cause up to 0.55 m (1.8 ft) of drawdown. Natural drainage of the aquifer caused the water table to decline 0.8 m (2.6 ft) over this same period. MODPATH simulations using this groundwater model indicate an average residence time in the aquifer of 13 years and a maximum residence time of 70 years. / text

Thesis (M.S.)--Texas State University-San Marcos, 2008. / Vita. Includes bibliographical references (leaves 60-67). Also available on microfilm.

"The problem investigated in this thesis is that of determining the impact of the disestablishment of Camp Edward Gary on the economy of the city of San Marcos, Texas...it is anticipated that this study may contribute two additional outcomes of value: the first is a test of certain ideas in economic theory pertaining to recessions; and the second is an evaluation of the data pertaining to the economy of small communities...the data presented in Chapter II and the summarization of that information in Chapter III lead to the inevitable conclusion that the deactivation of Camp Edward Gary caused a recession in the City of San Marcos, Texas, which was shared in varying degree by virtually every element of the economy...it is further concluded that the impact of the loss of the military community was modified to some degree by the beneficial effects of the growth in its educational institutions and the fact that the loss was shared, although in a lesser degree, by other communities in the general area." --leaves 4, 5, 79

The Barton Springs Segment, part of the karstic Edwards aquifer in Central Texas, is a Sole Source aquifer, is habitat to rare karst species, and provides water to a well-loved municipal swimming pool, yet its hydrogeologic properties remain insufficiently understood. For this study, the hydrogeologic characteristics of the Barton Springs Segment were investigated using several approaches, including mapping of hydrostratigraphic units and faults, measurement of upland infiltration, groundwater traces, and aquifer tests. The depositional environment, diagenesis, fracturing, down-dropped and dipping faulted blocks, and subsequent dissolution were determined to play important roles in controlling groundwater flow-path development within the Barton Springs Segment. In particular, downdropped fault blocks create groundwater gradients to the southeast that influence flow in the Edwards outcrop area. Upland internal drainage basins were found to be extremely efficient at conveying recharge to the underlying aquifer. The maturity of natural internal drainage sinkholes can be measured by its bowl volume, which grows in proportion to the catchment area it captures. A 19-hectare internal drainage basin, HQ Flat sinkhole, was monitored for rainfall, evapotranspiration, soil moisture, and discrete runoff to the cave drain. During a 505-day period, 5.5% of measured rainfall entered the cave drain as discrete recharge, 26% of measured rainfall infiltrated through soils on the slopes, and the remaining 68% was lost through evapotranspiration. This amount of upland infiltration is consistent with infiltration measurements in other karst areas and is much larger than the 1% upland recharge of rainfall that was previously estimated. A chloride mass balance indicates that at the adjacent Tabor research site, about 50% of rainfall infiltrates to a 6-meter depth. Dye-tracing and pump tests demonstrated that primary and secondary groundwater flow paths are the major influence on transmissivity within the Barton Springs Segment. Groundwater tracing breakthroughs reveal very high advection and relatively low dispersion. Drawdown response to pump tests indicates a very high degree of anisotropy, controlled by location of groundwater flow paths. Overall the Barton Springs Segment is a mature karst aquifer with highly developed rapid, discrete network for both recharge and groundwater-flow. / text