Browsing by Author "Davies, Bryan"

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    Defining flows to protect instream biota : a critique of the instream flow incremental methodology and the development of a hierarchical habitat-based approach, using the pennant-tailed catlet, Chiloglanis anoterus in the Marite River, South Africa
    (2001) Pollard, S (Sharon); King, Jackie; Davies, Bryan
    This thesis focusses on two approaches to determining Instream Flow Requirements (IFR) for regulated rivers, specifically in the sub-tropical eastern region of South Afiica using a flow-sensitive fish species, the pennant-tailed catlett 07iloglanis anoterus. In response to the diminishing and altered flow regimes of rivers, and the ecological consequences, a range of methodologies has evolved that attempt to quantify IFRs for rivers. One group of methods that attempts to do this are known as habitat-assessment approaches. They focus specifically on understanding how changes in river flow affect the quantity of physical instream habitat. The most widely used of these is the Instream Flow Incremental Methodology (lAM) and it's associated computer packages, PHABSIM II. More recently, South Africa has also turned its attention of ways to defining IFRs. Given lAM's prominence internationally, it was considered as one potential methodology. Nonetheless, its applicability to local conditions required testing. At the same time, the easterly-flowing rivers were under increasing development pressure, providing a particular immediacy to find appropriate means to define IFRs. Thus, my research was designed to assess the downstream effects of the Injaka Dam on the physical habitat of a flow-sensitive fish species of the Marite River. Specifically, it aimed to test the local applicability of lAM, based on the microhabitat requirements of C anoterus, and to explore an alternative approach if it were found to be unsuitable. Microhabitat is described on the basis of three hydraulic variables: depth, velocity and Channel Index (substratum and cover).
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    The ecology and control of typha capensis in the wetlands of the Cape flats, South Africa
    (1993) Hall, Deborah Jane; Davies, Bryan; Moll, Eugene
    Typha capensis is indigenous to the Cape, but is thought to be threatening Cape Flats wetlands through invasion and encroachment. This thesis establishes the extent of such encroachment and investigates aspects of the phenology, life-history, growth, production and decomposition of the species in a Cape Flats wetland. The process of invasion by indigenous species rather than by alien species is discussed and the view that wetlands are threatened by mismanagement rather than by encroachment per se is examined. Finally, control methods particularly suited to local environmental and economic conditions are evaluated. T. capensis was shown to be typical of invasive plant species and is spreading in some wetlands. Encroachment is usually associated with the stabilisation of seasonal water-level fluctuations and under these conditions stands were spreading at 1.5m month. Demographic methods used to measure growth, production and decomposition made it possible to quantify leaf fragmentation and shoot collapse, processes that are generally ignored during decomposition studies. Results showed that the structure of Typha stands is related to flood regime, and that flood regime has an important effect on production, litter formation and decomposition.
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    The ecology of some urban-impacted coastal vleis on the Cape Flats near Cape Town, with special reference to phytoplankton periodicity
    (1991) Harding, William R; Davies, Bryan
    This thesis stemmed initially from the author's desire to investigate the phytoplankton assemblages of the freshwater vleis of the Cape Peninsula. This aspect of the limnology of the Cape Flats vleis has received only scant attention by other researchers (over 40 years ago), and no comprehensive studies of their seasonal phytoplankton periodicities had been attempted. The paucity of information regarding the phytoplankton of the winter-rainfall, Mediterranean-climatic systems of the Cape Peninsula was found to not only be limited to South Africa. The literature survey undertaken for this study (Chapter 1) revealed•a general lack of information for shallow, nutrient-enriched, coastal systems, with virtually no data available for coastal systems in winter-rainfall regions. The thesis includes a description not only of the phytoplankton, but also of the limnology of each vlei as they are currently understood; this information is synthesized in Chapters 2 and 3 and collates all the available information accumulated by the Cape Town City Council (CCC) since it commenced monitoring of both vleis almost a decade ago. These chapters also contain details of the available bibliography for each system and form the first compilation of the available data for these waters. The inclusion of these chapters enabled comparisons to be made between the water chemistry regimes during the current study with those prevailing during earlier years. During the course of the study the author came across other pertinent aspects of each vlei which necessitated sub-investigations. The details of these are also included in the limnological chapters.
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    The effect of regulation by two impoundments on an acid, blackwater, Cape mountain stream
    (1992) Gale, Barbara Ann; Davies, Bryan
    The world-wide proliferation of dams in the last few decades has necessitated a fuller understanding of the effects of stream regulation but has also provided a setting for testing and developing basic theories of stream ecology. Two important concepts in stream ecology, the River Continuum Concept (RCC) and the Serial Discontinuity Concept (SOC), required investigation as to their applicability to entire river systems in the Southern Hemisphere. The RCC hypothesises that biological communities are structured in a predictable fashion from the source to the mouth of a river in relation to physical environmental gradients along the stream continuum. The SOC proposes that a major impoundment at any position on a river system will cause a longitudinal shift in a given parameter (physical or biological) which will cause a discontinuity in the stream continuum. A certain distance is then required for the stream to return to its normal position in the continuum, and this is termed a 'discontinuity distance'. The effect of regulation by multiple impoundment on the 'discontinuity' (recovery) 'distances' for various physical, chemical and biological attributes of the Palmiet River (a short, steep gradient, cool, acid, low nutrient system) was investigated in a two-year study. Two zones of the river were identified for study: one below an upper-reach impoundment, Nuweberg, and one below a middle-reach impoundment, Arieskraal, as they provided sufficiently long stretches of unperturbed river (7 km and 37 km) over which recovery distances could be investigated. Sampling was undertaken monthly for 27 months from February 1986 to April 1988. Eleven sites were chosen along the length of the river: one in the pristine upper reaches, one site above and 3 sites below Nuweberg, a site on the river as it passes through the village of Grabouw, one site above and three sites below Arieskraal and a site on a tributary, the Klein Palmiet, from which water is abstracted into Arieskraal. The values of the variables downstream of the impoundment are said to increase or decrease with respect to the "above-impoundment" value. Median temperatures, pH and alkalinity increased below Nuweberg, but decreased below Arieskraal, whereas the converse was true for soluble reactive phosphate. Seasonal flow regime reversal occurred below Nuweberg and seasonal flow constancy below Arieskraal; there were seasonal shifts in temperature and a dampening of the annual temperature range below both impoundments; and seasonal shifts in alkalinity below Arieskraal. At least partial recovery was noted in all cases, but in some instances, recovery was incomplete to the estuary.
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    Evaluating the user-experience of existing strategies to limit video game session length
    (2018) Davies, Bryan; Blake, Edwin
    Digital video games are an immensely popular form of entertainment. The meaningful positive experiences that games facilitate are fundamental to the activity; players are known to invest a lot of time playing games in search of those experiences. Digital games research is polarized. Some studies find games to be a healthy hobby with positive effects; games promote well-being through regular experience of positive psychological experiences such as flow and positive emotions. Others have identified rare problematic use in those players who devote excessive amounts of time to gaming, associating them with social dysfunction, addiction, and maladaptive aggression. While it remains unclear if games cause these effects, or merely coincide with play, the negative effects historically receive more attention in both popular media and academia. Some authorities attempt to reduce the harms associated with games to such an extent that their methods have become national policy affecting all players including those who exhibit no negative outcomes. In South Korea and Taiwan, policing authorities employ a behaviour policy that sets strict daily limits on session length, thereby controlling the amount of time people spend playing games each day. In China, the General Administration of Press and Publication employ a design policy requiring that games service-providers fatigue their games’ mechanics after a period to coax them to take a break sooner than they ordinarily would. Both policy types alter player interaction with games in any given session and it is unclear how these policies affect players in general. This research aims to compare sessions affected by the behaviour policy, design policy, and policy-free sessions in terms of session length, measurable subjective user-experience, the player's intention to return to the game, and their reasons for choosing to stop playing in a particular session. For use in a repeated-measures experiment, we modified the action RPG Torchlight II to simulate both policies. Participants had one session at the same time each week for three consecutive weeks. In varied sequences, participants played a control session unaffected by policy, a onehour shutdown session representing behaviour policy, and a fatigue session representing design policy. After each session, we recorded their session's length, their user-experience in terms of flow and affect, their intention to return to the game, and their reason for ending the current session. We found that our shutdown condition successfully decreases session length, when compared to the other conditions. The condition facilitates strong flow, moderate positive-affect, and weak negative-affect. The shutdown event does not appear to degrade positive experiences and makes participants slightly more upset (statistically significant) than they would be after choosing to stop playing. This is because players do not get to make that decision, and because players are unable to complete the goals they have set for themselves. Most players intended to play the game again immediately or sometime later in that same day, much sooner (statistically significant) iii Word Template by Friedman & Morgan 2014 than they would after choosing to stop. This also may be due to satisfaction associated with choosing to stop, or being unable to complete their self-set goals. We found that our fatigue condition increases session length when compared to the other conditions. This result contradicts the intentions associated with design policies: shorter sessions. The fatigue mechanics make the game more difficult, which increases the time required for players to complete the goals they have set for themselves, whether it is to complete a level, quest, or narrative sequence. The condition facilitates high levels of flow, moderate positive-affect and low negativeaffect; the condition does not appear to degrade these positive experiences, nor increase negative experience. Most players intended to take the longest breaks between sessions of at least one day, and although we observed that these were longer than the control condition, the differences is not statistically significant. We found that most participants chose to stop playing when the game stopped providing them with positive experiences, or begins to generate discomfort. A large group of participants chose to stop because another activity took priority. Few participants chose to stop because they were satisfied with their session. Less than one third of players explicitly referenced the fatigue mechanics in their decision to stop. Neither policy is holistically better than the other. Both provide strong positive experiences, and have different effects on session length. Whereas it appears that the fatigue condition fails to reduce session length, it also appears that players intend taking longer breaks between sessions, which may reduce total play-time across all sessions. Similarly, the shutdown condition may increase total play time, or at least bring it closer to normal amounts of play-time while also making players more upset. Our operational definition of user-experience is bi-dimensional, and does not include many experiential constructs commonly associated with digital games. During this research, several reliable and valid, and more representative experience measures became available. Any future work on this topic should make use of one of these. Our experiment tested the effects of player experience associated with a single game, genre, and context. Future research should reduce the variation of player factors by focusing on single personalities, typologies, or risk-factors rather than generalizing to all players. We tested out participants only as they played in the early stages of Torchlight II. It is possible that the game's narrative elements, rather than the gameplay mechanics fatigued by the design policy, motivated continued play. We suggest a longitudinal study of the individual policies to explore their effects over many sessions.
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    Late quaternary palaeoenvironments of the Sandveld, Western Cape Province, South Africa
    (1997) Baxter, Andrew James; Meadows, Michael E; Davies, Bryan
    This thesis presents new palaeoenvironmental evidence from the semi-arid lowlands of the West Coast Sandveld, which prompts a fresh synthesis as to the nature of late Quaternary environmental changes in the southwestern Cape's fynbos biome. The study is centred on Verlorenvlei, a remote coastal lake and swamp system which is ideally situated to investigate the complex interactions between late Holocene climate change, vegetation change, sea-level fluctuation, lacustrine/estuarine/fluvial sedimentology and human activity in the Sandveld region. In addition, this region of the West Coast has provided Quaternary scientists with a rich archaeological record against which independent lines of palaeoecological evidence can be evaluated. In support of the study, a wide range of palaeoenvironmental techniques has been applied to sediments sampled from the Verlorenvlei area. Organogenic deposits have been radiocarbondated and subjected to pollen analysis and assorted sedimentological and geoarchaeological assessments. Preliminary fossil pollen data from Elands Bay Cave, assembled for the period following the Last Glacial Maximum until approximately the terminal Pleistocene, are suggestive of moister and possibly cooler conditions in the Sandveld at this time. This is in contrast to prevailing evidence from the summer rainfall region of the subcontinent. Particle size analysis and an assessment of the in situ fossil Mollusca from vibracores, derived from the estuarine reaches of Verlorenvlei, reveal substantive evidence for rapid sea-level fluctuations along the West Coast during the mid-Holocene. Further inland, several mid-Holocene higher sea-levels are reflected in the palynology of lacustrine cores derived from Grootdrift and Klaarfontein. Detailed pollen diagrams, presented from Grootdrift, Klaarfontein, Muisbosskerm and Spring Cave, reflect the regional vegetation history during several periods over the last 7 000 years. There is convincing evidence from these data that the first half of the Holocene - commensurate with the Holocene hypsithermal - was associated with reduced moisture availability, and hence arid conditions along the West Coast. By contrast, there is evidence from the latter half of the Holocene that conditions ameliorated in the Sandveld around 3 000 BP and that moisture was, at this time more freely available. Following a hiatus in sedimentation some time after 4 000 BP, marine conditions are no longer visible in Verlorenvlei, having been replaced by fresh water as the dominant hydrological regime. A high resolution palynological investigation of the Grootdrift wetland sediments has contributed to a detailed palaeolimnological reconstruction of the upper Verlorenvlei system since the time of colonial expansion into the area, some 300 years ago. The picture reveals a sequence of rapid ecological changes in the face of progressive human disturbance. Arising from these insights, a number of recommendations for the management of dryland aquatic ecosystems such as Verlorenvlei, are presented. The significance of these late Quaternary palaeoenvironmental changes, in terms of the biogeography of plants and animals and also in terms of human occupation of the region, is examined.
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    A pre-impoundment study of the biological diversity of the benthic macro-invertebrate fauna of the Sabie-Sand River system
    (1992) Wells, Jay; Davies, Bryan
    The Kruger National Park (KNP) in the Eastern Transvaal provides a classic example of the potential conflict of interests between the industrial, agricultural and domestic sectors and conservation. The KNP is situated on the north-eastern border of South Africa and receives the flow of six rivers (Figure 0.1), all •of which originate outside the jurisdiction of the Park authorities. Thus, there are demands for water outside the boundaries of the KNP from other sectors of South Africa, as well as several self-governing states that have been set up as political entities within South Africa (see Chunnett, Fourie & Partners 1987, 1990). Due to human development •of catchments there has been regulation of these rivers, which are rapidly changing in terms of their flow regimes. (O'Keeffe. & Davies 1991). For example, the Letaba and the Luvhuvhu rivers have both changed from perennial to annual flow regimes (O'Keeffe & Davies 1991), a condition which is detrimental to the maintenance of river ecosystem functioning, while the Crocodile River has been regulated to an almost unvarying flow of ca 5m3 s•1 (O'Keeffe & Davies 1991). Recognising the need to address the problem of water allocation to the KNP, the Department of Water Affairs (DW A) convened a workshop on minimum flow needs for the environment in 1987 (Bruwer in press). Although tentative values were suggested for minimum flows, the value of the workshop was its recognition of the need for more research into the problem. Such research is currently being undertaken under the auspices of the multi-disciplinary KNP Rivers Research Programme. The goal of the programme is to " ... develop the means to predict the impact on the KNP river systems of changing flow regimes and water quality as the basis of a protocol for managing the• allocation of water for ecological purposes" (Kruger National Park Rivers Research Programme 1990). One of the studies initiated within this programme was a pre-impoundment study of the Sabie River, including its main tributary, the Sand River, which together are referred to as the Sabie-Sand River system.