The spatial distribution of local evaporation from ground-based sources behind solid and porous windbreaks was studied in laboratory models for steady state and intermittent flows. Field observations of wind and turbulence characteristics (turbulence intensity, power spectra and integral length scale L) over surfaces whose zero displacement (d) and roughness length (z$ sb0$) had also been determined, were used to scale the laboratory simulations. Scaling parameters were z/z$ sb0$, $ sigma$/U, L/z$ sb0$ and Uz$ sb{0}$/K, where z, U, $ sigma$ and K are height, wind speed, standard deviation of velocity fluctuations and turbulent diffusivity, respectively. The 50% porosity barrier was found to be the most effective single-barrier set-up for the reduction of moisture loss. / Conditional sampling of fluctuations w' and q' of the wind and moisture, respectively, with sonic anemometer and fast-response Krypton hygrometer behind solid and porous windbreaks in the field, revealed frequency of occurrence, duration and intensity of those turbulent structures primarily responsible for moisture transfer.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on September 25, 2009) Thesis advisor: Dr. Mary Grigsby. Includes bibliographical references.

No description available.

Call number: LD2668 .T4 1962 F79

In the Canterbury region, New Zealand, water is a contentious issue when irrigation and dairy farming are involved. The Canterbury region accounts for 70% of the total irrigated land area in New Zealand and is one of the most productive agricultural regions. Traditionally, water has been seen as an abundant resource, but growing water demands are now outstripping the supply of water, hence threatening the sustainability of agricultural productivity. In the long term, this problem may worsen as a result of climate change, which is predicted to increase water demands and reduce supply in many parts of Canterbury. In the recent and on-going expansion of irrigation systems, modern sprinkler irrigation methods, namely centre pivot and lateral spray irrigation technology, have replaced the old border-dyke systems. This has been due to the need to increase irrigation flexibility and efficiency to guarantee pasture growth for dairy production in dry periods. This conversion has resulted in a reduction of windbreaks to 2 m heights or sometimes led to 100% removal of windbreaks so as to accommodate centre pivot or linear move irrigation systems. Removal of windbreaks or reduction of windbreak height may increase wind speed across a field. Both spray evaporation loss and evapotranspiration are a function of wind speed. Hence, any increase in wind speed may lead to an increase in irrigation requirements. There is little information currently available on outlining how reduction of windbreak height or the complete removal of windbreaks affects efficiency in water application. Thus, this research was done to quantify the effects of windbreaks on water savings under sprinkler irrigation systems in the Canterbury region under various climatic conditions. The research was done in three major steps: (1) spray evaporation loss (SEL)was measured under various climatic conditions for two typical spray nozzles(Nelson Irrigation Corporation Rotator R3000 and Spinner S3000 nozzles) to develop SEL prediction models; (2) wind speed reduction behind windbreaks was quantified for fields under various wind conditions; and (3) the effects of wind speed reduction by windbreaks was modelled for evapotranspiration, spray evaporation loss and irrigation. The results showed that an increase of wind speed, due to the removal of windbreaks or a reduction of height of windbreaks, leads to an increase in evapotranspiration and spray evaporation losses in irrigated agriculture. For the size of the fields considered in this study which are 80 m by 80 m (Site 1 with medium porosity windbreaks) and 120 m by 120 m (Site 2 with low porosity windbreaks), extra irrigation water of up to 14% is needed in one growing season when windbreaks are reduced to 2 m in height. When windbreaks are completely removed from the field, extra irrigation water of up to 38% and 64% is needed when irrigating using the Rotator R3000 nozzle and the Spinner S3000 nozzle, respectively. Thus, reduction of water resource use can be achieved in irrigated agriculture if irrigation systems can be designed to operate under existing windbreaks. Other savings can follow, from reduced requirements for pumping, fuel and labour costs. Lastly, with future climate change projections showing that the Canterbury region will get windier and hotter, windbreaks can help mitigate water losses associated with sprinkler irrigation

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 138-169). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 138-169). Also available on the Internet.

Thesis (Ph. D.)--University of Florida, 2001. / Printout. Vita. Description based on print version record. Includes bibliographical references (leaves 218-234).

No description available.

No description available.