No description available.

No description available.

No description available.

Modeling ground-water hydrology is critical in low-gradient, high water table watersheds where ground-water is the dominant contribution to streamflow. The Hydrological Simulation Program-FORTRAN (HSPF) model has two different subroutines available to simulate ground water, the traditional ground-water (TGW) subroutine and the high water table (HWT) subroutine. The HWT subroutine has more parameters and requires more data but was created to enhance model performance in low-gradient, high water table watershed applications. The objective of this study was to compare the performance and uncertainty of the TGW and HWT subroutines when applying HSPF to a low-gradient watershed in the Coastal Plain of northeast North Carolina. One hundred thousand Monte Carlo simulations were performed to generate data needed for model performance comparison. The HWT model generated considerably higher Nash-Sutcliffe efficiency (NSE) values while performing slightly worse when simulating the 50% lowest and 10% highest flows. Model uncertainty was assessed using the Average Relative Interval Length (ARIL) metric. The HWT model operated with more average uncertainty throughout all flow regimes. Based on the results, the HWT subroutine is preferable when applying HSPF to a low-gradient watershed and the accuracy of simulated stream discharge is important. In situations where a balance between performance and uncertainty is called for, the choice of which subroutine to employ is less clear cut. / Master of Science

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1983. / Includes bibliographical references (leaves 117-120).

The relationship between vegetation change and rehabilitation management is investigated at a severely degraded cut-over lowland raised mire on the Wales/England border, managed by Natural England and The Countryside Council for Wales. Positive responses are confirmed 11 years after rehabilitation commenced, identifying trends towards raised mire as well as bog pool vegetation and water table thresholds associated with these trends have been established. A landscape-scale vegetation survey was carried out three times over 9 years. Species abundance was correlated with average seasonal water table height, time since rehabilitation, cutting type and survey year. Key species maps for the time series confirmed positive vegetation response, but slower than stipulated in the site management plan. There was a clear increase in the target peat-forming species (Sphagnum cuspidatum, Eriophorum angustifolium and E. vaginatum) as a direct response to rehabilitation and correlating positively with a high water table. Permanent quadrat vegetation monitoring was carried out three times at five-year intervals. Uncut areas and areas of recent commercial cuttings were rehabilitated earliest having significant increases in target mire species without the loss of other mire species from excess inundation. In the recent commercial cutting areas, a successional trend was identified, from a low water table to a fluctuating water table characterised by Molinia caerulea-rich vegetation, followed by a transition to stable, inundated conditions supporting Sphagnum cuspidatum/Eriophorum spp pool vegetation. A second successional trend, associated with the achievement of a near-surface, stable water table, saw the development of raised mire vegetation including Sphagna other than S. cuspidatum. This latter trend was primarily found in the uncut areas of the site but was also found to a lesser extent in recently cut-over areas where it was preceded by a fluctuating water table with a Calluna vulgaris- Molinia caerulea vegetation. A new survey related water table residence time calculated from hydrology data with vegetation for each quadrat. Analysis identified a mire pool vegetation type correlated with shallow, above surface flooding. A diverse mire vegetation type was also found which correlated with the water table staying within the upper 10cm of peat. The minimum threshold for establishment of Sphagnum species was found to be an average water table level within the range of 5.1 to 10cm below the peat surface. Higher cover of Sphagnum species was related to shallow flooding – suggesting that these conditions would be most efficient in re-establishing mire vegetation. 3 A base-line vegetation monitoring survey on an area immediately following deforestation and damming identified a subtle but positive response of the mire vegetation to management within one year.

This thesis describes the flow of ground water with a free water table, in an isotropic and homogeneous soil overlying a horizontal impermeable layer, from a surface-applied rainfall or irrigation supply to a system of horizontal tube drains. The idealized representation of this situation is in terms of a potential flow towards line sinks. The tube drains (sinks) may be at atmospheric pressure (free flow) or under back-pressure (submerged flow). After describing the flow to systems of drains at uniform depth and equal spacings, the thesis shows the effect of horizontal, vertical and combined misalignments of a single line sink on the free surface, the flow pattern and the rates of flow to each sink. The study was carried out by viscous-flow and electrical analogues, by a numerical method (Relaxation), and by the exact solution of equations based on physical approximations. In theory the extent of the effect of any misalignment is infinite. Experimentally it was found that the vertical misalignment had a significant effect on the free surface, discharge and flow net over the whole range of the experiment, while the horizontal one had a noticeable effect only extending over one spacing on either side of the misaligned drain. An approximate mathematical solution for the horizontal displacement has been obtained. Experiments on the viscous-flow model revealed the importance of the effect on the free surface etc. of the back pressure. The distribution of the effect along the free surface and the correlation between the free surface height and the back pressure are also presented. A new approach was used to elucidate the effect of negative pressure (capillary rise) on the free surface and obtain the surface of atmospheric pressure. An equation, independent of the geometrical scale ratio was derived to relate the various parameters for the unsteady flow to the scaling laws. The introduction of a reference potential at a fixed point in the field provides a method for the correction of the change with time in the position of equipotentials and represents a new technique. The variations of free surface heights with discharge, as observed on the viscous-flow model, were compared with the results of s some recent theories and showed discrepancies between the experiment and theories.

In a shallow aquifer underlain by low permeable material, groundwater recharge (R), discharge to rivers or stream as baseflow (BF), and discharge to the atmosphere as evapotranspiration (ET) are related by a simple water balance equation, R - ET - BF = ΔS. Gathering information about these processes is difficult since these processes are hidden from view, yet these processes commingle with one another at the water table surface. The main objective of this dissertation project was to evaluate how main hydrological processes can be inferred from high-resolution water table measurements collected at various sites in Walnut Creek watershed located in southern Iowa. Water table monitoring data available for analysis in the project included three main sites, covering 2573 days between 1996 to 2008 and 61,714 individual water level monitoring points. Water table fluctuations were used to estimate R across an upland-floodplain chronosequence and plant ET under three riparian land covers. High resolution hydraulic head measurements were analyzed with spectral methods to evaluate potential surface and groundwater interaction. Detailed sedimentology and water table monitoring were combined to develop a conceptual model of nitrate leaching to in the near-stream riparian zone of an incised channel. Additional soil moisture and precipitation monitoring are recommended for improved application of methods to other sites. Results from this dissertation indicate that there is a considerable amount of information about key hydrological processes to be gained by measuring water table levels at a high frequency.

The lack of cost-effective, reliable sampling methods for many wetland characteristics hinders efforts to describe the structural and functional properties of wetlands. This study evaluated techniques for sampling the subsurface hydrology and invertebrates of freshwater wetlands. The depth of rusting on mild steel rods was compared with water well measurements to determine the reliability of rust depth as a predictor of subsurface water levels. An emergence trap and a benthic coring device were compared to determine the utility of each for sampling the invertebrate fauna of a wetland. Accuracy of the rods in estimating different water table measurements (average, lowest, most recent) and comparability of rod data (within sets of five rods) were investigated for different reference points on the rods, residence times, and wetland soils. The effect of the presence of vegetation in a soil low in organic matter on rod accuracy also was evaluated. The depth of lowest formation of a rust band on the rods predicted average and most recent water table depths in peat soil (r² for regressions of rust band depth on water table depth ranged from 0.71-0.95). Estimates of average water table depths were most precise for peat soil. Accuracy and precision were considerably lower in sand and clay soils, but significant relationships (P < 0.10) between depth of rust band formation and water table depth were found for all soils (r² values for sand and clay ranged from 0.13-0.55). The presence of vegetation had no effect on rod accuracy in the sand soil. Differences in rod performance between residence times were not apparent. However, a rod residence time of 4-6 weeks is recommended to balance the time necessary for adequate rust formation on the rods and to minimize the chance of exposure to large changes in water levels. A decrease in water table depth of approximately 40 cm in one month in the clay wetland caused a month lag time in rust formation. Differences in depth of rust band formation between the five rods within replicate sets were greatest for rods from clay (mean SD = ±7.9 cm). Variability of rust band measurements within replicate sets was lower in peat (mean SD = ±2.3 cm) and sand (mean SD = ±2.6 cm). The results indicated that the rusty rod technique has serious limitations and should be applied only in situations where the use of standard methods must be restricted. Emergence traps and a benthic coring device were used to sample the invertebrates of a freshwater, emergent wetland during late spring and summer, 1989. The fauna captured by each technique, disparities between the techniques in sampling certain taxa, and factors potentially affecting abundance estimates were examined. In addition, the efficiency of each technique, expressed as the number of samples required to achieve a desired level of precision, in estimating mean abundances of the dominant invertebrate group, the Chironomidae, was evaluated. Total and monthly estimates of insect family richness were higher for continuous sampling of emergence than for monthly core samples of the benthos. Emergence traps also caught a greater variety of the insect taxa inhabiting the wetland. The precision and efficiency of each technique in estimating abundances of the dominant group, the Chironomidae, varied between months and habitats (open water; vegetation). The variation was most likely due to the natural spatial and temporal variations inherent in invertebrate populations. The number of samples required (n[subscript r]) to estimate mean Chironomidae abundances for the entire summer, June-September, to a precision of D= 0.20 (equivalent to a standard error equal to 20% of the mean), varied between techniques. Fewer sampling stations would have been required to estimate mean adult abundances using emergence traps than would have been required for estimates of larval abundances using benthic core samples. Large numbers of benthic cores (27-208 individual cores per habitat) would have generally been required for both monthly and seasonal estimates of non-insect invertebrate abundances. Labor costs for processing emergence samples were about 30% of those for benthic samples. Subsampling of dominant groups in the emergence samples would have further reduced costs. Frequent sampling throughout a season, with several different techniques, is required to completely characterize the invertebrate community of a wetland. This study compared two quantitative techniques for sampling wetland insects. Continuous sampling with emergence traps provided higher estimates of insect family richness and more precise estimates of Chironomidae abundances at a lower cost per sample than monthly core samples of the benthos. / Graduation date: 1992

Irrigation rates in excess of plant evapotranspiration requirements have been identified as a major contributor to the development of raised water tables in the City of Lethbridge. These high water tables have created problems such as coulee slope instability, basement flooding and structural instability. This study characterized water table conditions in Lakeview subdivision, an area that experiences basement flooding. Soil texture data from this subdivision is used to address speculation that geologic controls contribute to high water tables in the city of Lethbridge, Linear regression analysis comparing mean sand and clay fractions to mean water table depth revealed that variations in soil texture have no statistical relationship to variations in water table depth. Glacio-lacustrine sediments underlie Lakeview subdivision while tills predominate in the Varsity Village area. Lakeview subdivision is also approximately 20 years older than Varsity Village and the two are compared to gain some understanding of how water tables develop over time. Comparison of mean water table depths in irrigated and non-irrigated land cover classes in both Varsity Village and Lakeview revealed a significant difference in Varsity Village whilc Lakeview showed no statistical difference. Finally, a water scheduling program is developed to decrease or reduce the build-up of water tables and alleviate some of the problems that result. / x, 169 leaves : ill. ; 29 cm