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Thesis (Ph. D.)--Technische Universiteit Delft, 1988. / Vita. Includes bibliographical references.

Thesis (M.Sc. Agriculture (Soil Science)) -- University of Limpopo, 2021 / Woody plant encroachment results in the degradation of grasslands. It is defined here as the increase in density, cover and biomass of woody plants into formerly open grasslands, reducing grassland productivity. Globally, many arid and semi-arid savanna grasslands are affected by this land cover transformation which changes the vegetation structure by altering the ratio of woody plants relative to grass species and influences soil hydrology. In the existing literature there is limited information on the effects of woody plant encroachment on soil physical and hydrological properties, especially in savanna grasslands. This study quantified and compared the soil physical and hydrological properties in the topsoil and subsoil of open and woody plant encroached grassland sites located on two contrasting soil forms, namely Bainsvlei and Rensburg. To achieve this objective, the two soils were sampled at various depth intervals from dug soil profiles at both sites at Towoomba Research Station in Bela Bela, Limpopo Province, South Africa. Soil physical properties including bulk density, porosity and aggregate stability as well as hydrological properties (water retention and hydraulic conductivity) were determined from collected samples. Compared to open grassland, soil bulk density was 11% and 10% greater in the topsoil and subsoil, while porosity was respectively 6% and 9% lower in the topsoil and subsoil of woody plant encroached grassland for Rensburg soils. In Bainsvlei soil, there was a minimal increase and decrease in the soil bulk density and porosity, respectively. Soil aggregate stability increased by 38% in the subsoil of woody plant encroached grasslands in Rensburg soil, due to increasing clay content with depth. In Bainsvlei soil, the soil aggregate stability was 9% and 13% lower in the topsoil and subsoil of the woody plant encroached grasslands compared to open grassland. Furthermore, the results revealed that in both soils, there was lower soil water retention and hydraulic conductivity in the topsoil and subsoil layers of woody plant encroached grassland than in open grasslands. There were no significant differences observed for soil hydraulic conductivity in the Bainsvlei and Rensburg topsoil. The subsoil hydraulic conductivity decreased by 24% in Bainsvlei and 44% in Rensburg soils in the woody plant encroached grassland. The soil water retention (SWR) decreased with an increase in woody plants. Specifically, there was 25% and 42% decrease in SWR with woody plant encroachment in the topsoil and subsoil of Bainsvlei soil, respectively. The same trend was observed in the Rensburg soils with 50% and 19% decrease in SWR in the topsoil and subsoil, respectively. Overall, the results revealed that soil type and depth influenced soil physical and hydrological properties in the studied woody plant encroached savanna grassland. As such, interventions aimed at controlling woody plant encroachment need to factor in soil type and depth in the development of management practices tailored to improve the soil hydrology of savanna grasslands

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From the Proceedings of the 1971 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 22-23, 1971, Tempe, Arizona / The southern bed of the ogallala aquifer is hydrologically isolated from all outside areas of recharge, requiring local precipitation for all natural recharge. Current withdrawals are so much greater than natural recharge that it appears that artificial recharge affords the only means of establishing at least a pseudo-balance. A number of observation wells were drilled at Texas Tech University, and subsequently capped until recharge water became available. The initial recharge was 2.5 af over 12 days, at a rate of 120 gpm for about the first day, after which 60 gpm was relatively constant. Approximately 1 month later, 1.2 af were recharged over 3 days at rates ranging over 140-90 gpm. It became evident that a cavity was present at the bottom of the hole being recharged. On a later recharge occasion, the cavity seemed to have enlarged. During a period of 2 years more than 28 af of surface runoff water have been recharged through the shallow hole with increases in recharge rates for each subsequent recharge period. The nature of this phenomenon and the cavities are not understood. This may represent the long sought after answer to recharge of the aquifer, but much more extensive research needs to be done.