Methods for design flood estimation in South Africa

The estimation of design floods is necessary for the design of hydraulic structures and to quantify the risk of failure of the structures. Most of the methods used for design flood estimation in South Africa were developed in the late 1960s and early 1970s and are in need of updating with more than 40 years of additional data currently available and with new approaches used internationally. This paper reviews methods used for design flood estimation in South Africa and internationally and highlights research needs in order to update the methods used for design flood estimation in South Africa

The development and assessment of a regionalised daily rainfall disaggregation model for South Africa

The temporal distribution of rainfall, viz. the distribution of rainfall intensity during a storm, is an important factor affecting the timing and magnitude of peak flow from a catchment and hence the flood-generating potential of rainfall events. Rainfall intensity is also one of the primary inputs into hydrological models used for the design of hydraulic structures. In the absence of continuously recorded rainfall data, one method of estimating the temporal distribution of rainfall is to disaggregate coarser-scale data into a finer resolution, e.g. from daily data into hourly rainfall information. In this study, a daily to hourly disaggregation model developed in Australia, and modified for application in South Africa, is used. However, this model requires input obtained from short-duration data at the desired location. Owing to the paucity of short-duration data in South Africa, the methodology is regionalised to enable the application of the model at a national scale, particularly at locations where only daily data are available. The regionalised model was independently tested at 15 locations in differing climatic regions in South Africa. At each location, observed hourly data were aggregated to yield daily values and were then disaggregated using the methodology. Results show that the regionalised model is capable of replicating the results obtained when ‘at-site’ short duration rainfall data are used as input to the disaggregation model, and is able to retain the daily totals and the statistical characteristics of the hourly rainfall.Keywords: temporal rainfall disaggregation, regionalisation, South Afric

A hydrological perspective of the February 2000 floods : a case study in the Sabie River catchment

The exceptionally heavy rains which fell over the north-eastern parts of South Africa, Mozambique and Zimbabwe during February 2000 resulted in disastrous flooding, loss of hundreds of lives and severe damage to infrastructure. The objective of the study reported in this paper is to assess the severity, from a probabilistic perspective, and spatial variability of the extreme rainfall and flooding which occurred in the north-eastern part of South Africa during February 2000. This is performed for events ranging from 1 to 7 days in duration using the Sabie River catchment, upstream of the South African/Mozambique border, as an example. The analyses indicate that the floods experienced in the Sabie catchment during February 2000 were the result of rare rainfall with return periods in excess of 200 years in parts of the catchment. The extent of the extreme rainfall increased for longer durations. The magnitudes of the February 2000 floods were such that many gauging stations did not function and numerous gauging structures were inundated. Hence, a modelling approach was adopted to investigate the spatial variability, magnitudes and probabilities of the floods which occurred during February 2000 in the Sabie catchment. The return periods of simulated runoff depths for durations of 1 to 7 days generally exceeded 50 years for the upper and middle portions of the catchment and 200 years in some parts of the Sabie catchment. Hence, some extremely large and rare flow depths were experienced and the spatial variability of the return periods associated with the simulated runoff depths varied substantially within the catchment. WaterSA Vol.27(3) 2001: 325-33

A catchment-scale irrigation systems model for sugarcane Part 1: Model development

In South Africa, the demand for water exceeds available supplies in many catchments. In order to justify existing water requirements and to budget and plan in the context of growing uncertainty regarding water availability, a model to assist in the assessment and management of catchment water supply and demand interactions, and the associated impacts on theprofitability of irrigated sugarcane, has been developed. The model, ACRUCane, operates as a submodel within the ACRU agrohydrological model and simulates the water budget of a field of irrigated sugarcane. The water budget is based on the integration of several widely accepted algorithms and concepts, accounts for different irrigation system types performing at different levels of uniformity and different water management strategies. Furthermore, it can simulate a wide variety ofwater availability scenarios and constraints through its link with ACRU simulated hydrology. The crop yield algorithms used in the model were verified using data from three different irrigation trials with widely varying irrigation treatments, where the model was shown to adequately distinguish the impacts of different watering strategies on crop yields. A description of the model algorithms and results from verification studies are presented in this paper. Application of the model is presentedin a companion paper

Development and assessment of a daily time-step continuous simulation modelling approach for design flood estimation at ungauged locations: ACRU model and Thukela Catchment case study

The estimation of design floods is necessary for the design of hydraulic structures. Commonly used event-based approaches to design flood estimation have several limitations, which include the estimation of antecedent soil moisture conditions and the assumption that the exceedance probability of the design flood is the same as the exceedance probability of the design rainfall. Many of the limitations of event-based approaches may be overcome by the use of continuous simulation modelling for design flood estimation. This paper contains a brief summary on the development and assessment of a continuous simulationmodelling system for design flood estimation in ungauged catchments. These developments include an investigation into the appropriate spatial scale of model configuration for optimum performance of the system, the temporal disaggregation of daily rainfall for hydrograph generation, flood routing in ungauged catchments and the use of radar information and rain-gauge data to improve the estimation of catchment rainfall. Results from the application of the system for design flood estimation in the Thukela Catchment in South Africa are presented and discussed. The results from the study highlight the challenges of hydrological modelling in an operational catchment and the need for reliable rainfall and runoff data. From the results obtained, it is concluded that reasonable and consistent estimates of design floods in the Thukela Catchment, particularly in smaller sub-catchments, can be obtained using the ACRU model.Keywords: Design flood estimation; continuous simulation modelling, Thukela Catchmen

Going, Going, Gone: A Feminist Bourdieusian Analysis of Young Women's Trajectories in, Through and Out of Physics, Age 10–19

This chapter draws on longitudinal interview data collected from seven young woman in England who were tracked from age 10–19 and who had all expressed an aspiration at age 16 to study Advanced level (A level) physics. Applying a feminist Bourdieusian conceptual lens, we explore their trajectories in, through and out of physics: from Danielle, who is denied entry to A level physics; to Victoria and Thalia, who are debarred from the course before completion; to Davina, Kate and Mienie, who complete the A level but who choose not to pursue the subject further; and finally Hannah, who goes on to study physics at university. Attention is drawn to the pedagogic work conducted by the field of physics, notably the cultivation of habitus and hexis through the bodies, minds and identities of the young women, and its stringent gate-keeping practices, which ensure the reproduction of the elite status of the field and the simultaneous disadvantaging of women

Minimally invasive surgery and cancer: controversies part 1

Perhaps there is no more important issue in the care of surgical patients than the appropriate use of minimally invasive surgery (MIS) for patients with cancer. Important advances in surgical technique have an impact on early perioperative morbidity, length of hospital stay, pain management, and quality of life issues, as clearly proved with MIS. However, for oncology patients, historically, the most important clinical questions have been answered in the context of prospective randomized trials. Important considerations for MIS and cancer have been addressed, such as what are the important immunologic consequences of MIS versus open surgery and what is the role of laparoscopy in the staging of gastrointestinal cancers? This review article discusses many of the key controversies in the minimally invasive treatment of cancer using the pro–con debate format

Intraperitoneal drain placement and outcomes after elective colorectal surgery: international matched, prospective, cohort study

Despite current guidelines, intraperitoneal drain placement after elective colorectal surgery remains widespread. Drains were not associated with earlier detection of intraperitoneal collections, but were associated with prolonged hospital stay and increased risk of surgical-site infections.Background Many surgeons routinely place intraperitoneal drains after elective colorectal surgery. However, enhanced recovery after surgery guidelines recommend against their routine use owing to a lack of clear clinical benefit. This study aimed to describe international variation in intraperitoneal drain placement and the safety of this practice. Methods COMPASS (COMPlicAted intra-abdominal collectionS after colorectal Surgery) was a prospective, international, cohort study which enrolled consecutive adults undergoing elective colorectal surgery (February to March 2020). The primary outcome was the rate of intraperitoneal drain placement. Secondary outcomes included: rate and time to diagnosis of postoperative intraperitoneal collections; rate of surgical site infections (SSIs); time to discharge; and 30-day major postoperative complications (Clavien-Dindo grade at least III). After propensity score matching, multivariable logistic regression and Cox proportional hazards regression were used to estimate the independent association of the secondary outcomes with drain placement. Results Overall, 1805 patients from 22 countries were included (798 women, 44.2 per cent; median age 67.0 years). The drain insertion rate was 51.9 per cent (937 patients). After matching, drains were not associated with reduced rates (odds ratio (OR) 1.33, 95 per cent c.i. 0.79 to 2.23; P = 0.287) or earlier detection (hazard ratio (HR) 0.87, 0.33 to 2.31; P = 0.780) of collections. Although not associated with worse major postoperative complications (OR 1.09, 0.68 to 1.75; P = 0.709), drains were associated with delayed hospital discharge (HR 0.58, 0.52 to 0.66; P < 0.001) and an increased risk of SSIs (OR 2.47, 1.50 to 4.05; P < 0.001). Conclusion Intraperitoneal drain placement after elective colorectal surgery is not associated with earlier detection of postoperative collections, but prolongs hospital stay and increases SSI risk

Loss of coral reef growth capacity to track future increases in sea level

Water-depths above coral reefs is predicted to increase due to global sea-level rise (SLR). As ecological degradation inhibits the vertical accretion of coral reefs, it is likely that coastal wave exposure will increase but there currently exists a lack of data in projections concerning local rates of reef growth and local SLR. In this study we have aggregated ecological data of more than 200 tropical western Atlantic and Indian Ocean reefs and calculated their vertical growth which we have then compared with recent and projected rates of SLR across different Representative Concentration Pathway (RCP) scenarios. While many reefs currently show vertical growth that would be sufficient to keep-up with recent historic SLR, future projections under scenario RCP4.5 reveal that without substantial ecological recovery many reefs will not have the capacity to track SLR. Under RCP8.5, we predict that mean water depth will increase by over half a metre by 2100 across the majority of reefs. We found that coral cover strongly predicted whether a reef could track SLR, but that the majority of reefs had coral cover significantly lower than that required to prevent reef submergence. To limit reef submergence, and thus the impacts of waves and storms on adjacent coasts, climate mitigation and local impacts that reduce coral cover (e.g., local pollution and physical damage through development land reclamation) will be necessary