published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

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Much research activity is carried out to reduce water consumption for domestic purposes. This leads to the possibility of reducing the amount of water introduced into building drainage systems. However, an accurate estimation of the flow attenuation within building drainage pipes is of great importance to prevent solid eposition and subsequent blockage. The research is focused on the field of subcritical flow in partially-filled pipes. Experimental and numerical investigations have been carried out to study the wave attenuation in the following configurations encountered in drainage pipe systems: i) A simple pipe, ii) A pipe subject to one concentrated lateral inflow, iii) A pipe with gate fixed at the downstream section, generating an interaction between wave and backwater profiles. In the present study the Saint-Venant equations are derived in their general and characteristic forms. A number of numerical procedures for solution of the Saint-Venant equations are reviewed, and the rectangular grid characteristics method, diffusing scheme and Strelkoff's implicit method are chosen to solve the equations. The stability of the finite-difference methods used is investigated for free-outfall and controlled outfall boundary conditions. An experimental installation consisting of 0.105 m diameter uPVC pipe is used to investigate the characteristics of the flow and to form test cases for the numerical methods. Comparisons between computed and observed depth hydrographs, peak depths and depth variations along the pipe are made for subcritical flow in a pipe of slope 1/300. The rectangular-grid characteristics method and the diffusing scheme are also applied to supercritical flow. Flow tests are undertaken for supercritical flow in a pipe of slope 1/200 to validate the use of these methods. The investigation revealed that the attenuation rate of peak depths is affected by the volume of the waves. The implicit method is the most suitable method, dealing efficiently with most problems encountered in drainage pipe systems of flat slope. The diffusing scheme can model the attenuation of supercritical flow within building drainage pipes.

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An innovative research study was established at IGER, North Wyke, Devon, to investigate preferential flow through a poorly structured relatively impermeable soil. Macropore channels were added by a mole plough in order to investigate soil water pathways and chemical transport in a soil in which preferential flow was guaranteed. The investigation focused on water and solute movement through specific flowpaths, namely macropores and mesopores, and the interaction between mobile and immobile zones within the soil. Two large soil blocks (1 m2 by 0.85 m) of the Hallsworth series were removed from the field and placed on sand tables so that a suction could be induced at the base of the soil block. The edge was sealed using paraffin wax. Eight tensiometers and suction cup lysimeters were installed in each block together with fifteen pairs of time-domain reflectometry wave guides. A regular spacing pattern was employed so that spatial variations could be easily identified. Samples were collected from suction cup lysimeters every 4 hours. Soil water status was observed from the TDR probes daily and from tensiometers every 10 minutes. Five tracer experiments were conducted; three involved the miscible displacement of chloride at concentrations of 100 and 250 mg I"' and two used nitrate (500 mg l ') and chloride (2500 mg 1') applied as a pulse. Tracer and irrigation water was applied through a misting system at an irrigation rate of 2.76 mm h-1. Three techniques were used to examine soil structure in the macropore and mesopore pore size range to investigate potential flowpaths in more detail. The profile tracing method (PTM). binary transect method (BTM) and resinated core section method (RCSM) provided useful quantitative structural information. Soil water status averaged over a large sampling volume (TDR, 1540000 mm3) was considered to be stable through time. Detailed observations of soil water suction using tensiometers showed that soil water conditions remained unsaturated, at approximately 10 to 20 cm H2O, and varied by 3 cm H2O throughout the experiment. Suction varied depending on the location of each tensiometer with respect to position within or between aggregates. Results based on Poiseuille's law and suction data showed that the flowpaths were predominantly mesopores. This result was supported by breakthrough curve analysis for the bulk of the soil although macropore flow was observed towards the mole drain. Flow rates observed from tracer movement varied throughout the soil regardless of depth. Chloride moved quickly towards the mole drain and the arrival of tracer was recorded within 4 hours. Time to breakthrough monitored at the suction cups varied from 4 to 76 hours. When the concentration gradient between applied solute and antecedent solute was large, reduced time to attain peak concentration was noted. As the concentration gradient reduced, speed of rise to peak concentration increased. An advection-dispersion model (CLEARY) fitted change in observed solute concentration through time at the suction cup lysimeters well. The study concluded that although water moved rapidly through the soil, the tortuous nature and increased contact with soil particles encountered as water moved through the mesopores resulted in water with matrix flow solute characteristics.

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The changes that have taken place in the British Coal Industry over the last five years have meant that in many coalfileds the last deep mines have closed. When a coalfield is abandoned and dewatering ceases, groundwater levels rebound, threatening surface waters with polluting discharges. However, the sparse data sets available limit modelling with existing techniques. A lumped parameter model GRAM (Groundater Rebound in Abandoned Mineworkings) has been developed. This model conceptualises a coalfield as a group of 'ponds'. Each pond is an area of the coalfield that has been extensively worked and can be considered as a single hydraulic unit. The ponds are connected by pipes which represent major inter-connecting roadways along which flow is assumed to be turbulent. Discharge to the surface is also represented using pipes. Flow through the pipes can be calculated using the Prandtl and Nikuradse of the Colebrook-White pipeflow equations. The storage coefficient can vary vertically to represent both worked Coal Measures and the intervening unworked strata. GRAM is able to predict the timing and volume of discahrges. An iron component gives an indication of the water quality evolution of the discahrges. Monte Carlo simulation allows the variables that have most error in their estimation to be represented by probability distributions. The Dysart-Leven Coalfield in eastern Fife, Scotland has not been mined since 1985. However, dewatering has continued to protect the workings in the Frances Colliery. In 1994 British Coal decided the Frances would never reopen, there is therfore no longer a need to continue dewatering. GRAM has been used to produce estimates of the quantity, timing and location of dischargges from the Dysart-Leven Coalfield should pumping cease. MODFLOW has also been applied to the coalfield with less success. Water quality modelling was also attempted using GRAM's iron component, however, conclusive results will not be obtained until the three variables over which ther is most uncertainty have been calibrated against existing discharges.

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Bibliography: p. 368-375. / xv, 375 p. : ill. (chiefly col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Laboratory tests using a wide range of additives have been undertaken to develop hardpans more akin to naturally occurring duricrusts. Some additives have developed cements which have the low permeability and porosity characteristics required, while maintaining a high level of resistance to both chemical and physical breakdown. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 1999