Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4045
Praval Maharaj, Elena Friedrich
Rainwater harvesting (RWH) provides a unique opportunity for water conservation. This research aimed to assess the performance of two types of RWH systems (gravity and pump-driven) at a local public school in replacing non-potable water for toilet flushing. The volume of harvested water, efficiency to meet demand, expenses involved and associated environmental burdens were key criteria of performance. Economic considerations included capital costs and return periods, while the environmental aspects encompassed simplified life cycle assessments (LCAs) as well as specific carbon footprints. The gravity-fed system supplied 452.5 kL/annum and covered 31.8% of the demand for flushing water for toilets for the school investigated. The pumped system provided 476.8 kL/annum representing 33.5% of the demand. Together they would be able to supply 65.3% of the demand. The catchment area of these two systems differed and there was no overlap. As expected, the gravity-fed system outperformed the pumped system, both economically and environmentally, because no energy for pumping was needed. In terms of costs, the difference was small, and the payback periods of both systems were similar. However, environmentally, the LCA scores for the pumped system were an order of magnitude higher for all 18 impact categories considered. Carbon footprints showed that in the construction stage both systems have similar footprints. For the operation stage, the comparison was extended, as there were higher energy requirements for the pumped system (about 4 times higher than those from the provision of municipal potable water), but in the same range or lower when compared with other alternative sources of water like groundwater abstraction, recycling of municipal water and desalination. The gravity-fed system required no energy for pumping. This study shows how trade-offs in assessing the overall performance of RWH systems can be considered, leading to better decision making.
{"title":"Environmental life cycle, carbon footprint and comparative economic assessment of rainwater harvesting systems in schools – a South African case study","authors":"Praval Maharaj, Elena Friedrich","doi":"10.17159/wsa/2024.v50.i1.4045","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4045","url":null,"abstract":"Rainwater harvesting (RWH) provides a unique opportunity for water conservation. This research aimed to assess the performance of two types of RWH systems (gravity and pump-driven) at a local public school in replacing non-potable water for toilet flushing. The volume of harvested water, efficiency to meet demand, expenses involved and associated environmental burdens were key criteria of performance. Economic considerations included capital costs and return periods, while the environmental aspects encompassed simplified life cycle assessments (LCAs) as well as specific carbon footprints. The gravity-fed system supplied 452.5 kL/annum and covered 31.8% of the demand for flushing water for toilets for the school investigated. The pumped system provided 476.8 kL/annum representing 33.5% of the demand. Together they would be able to supply 65.3% of the demand. The catchment area of these two systems differed and there was no overlap. As expected, the gravity-fed system outperformed the pumped system, both economically and environmentally, because no energy for pumping was needed. In terms of costs, the difference was small, and the payback periods of both systems were similar. However, environmentally, the LCA scores for the pumped system were an order of magnitude higher for all 18 impact categories considered. Carbon footprints showed that in the construction stage both systems have similar footprints. For the operation stage, the comparison was extended, as there were higher energy requirements for the pumped system (about 4 times higher than those from the provision of municipal potable water), but in the same range or lower when compared with other alternative sources of water like groundwater abstraction, recycling of municipal water and desalination. The gravity-fed system required no energy for pumping. This study shows how trade-offs in assessing the overall performance of RWH systems can be considered, leading to better decision making.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140482767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4046
Sagwati E Maswanganye, Timothy Dube, Nebo Jovanovic, Evison Kapangaziwiri, Dominic Mazvimavi
Non-perennial rivers (NPRs) have three hydrological states; each state has its importance, function and implication for water resource management. The dynamics of these states have been inadequately assessed and understood. Hence, this study sought to determine the spatiotemporal variations in the hydrological conditions of NPRs, focusing on the Touws River–Karoo drylands and Molototsi River within the semi-arid region of the Limpopo Province of South Africa. Additionally, the study aimed to delineate and characterize the primary areas contributing to runoff in these two river systems. Sentinel-1 and Sentinel-2 satellite data sources were employed in this study. Specifically, the modified normalized difference water index (MNDWI) derived from Sentinel-2 was utilized to delineate water surface areas along the two rivers. Subsequently, these derived datasets were utilized to assess the hydrological states over a 32-month period (2019–2022). Based on the presence of water, the river's state was classified as flowing, pooled, or dry. The results showed that remote sensing can be used to determine the hydrological state of the two river systems with ~90% overall accuracy. However, there is about a 30% chance that a flow event can be missed using Sentinel-2 due to clouds and temporal resolution. Some of these gaps can be filled using synthetic aperture radar (SAR) data (Sentinel-1), as demonstrated with the Molototsi River. In the Molototsi catchment, the upper catchment contributes the majority of flows. For the Touws River, the southwestern part of the catchment was determined as the major contributing area for the observed flows. This suggests that the chosen observation site might not be representative of upper catchment dynamics; therefore, a monitoring site in the upper catchment is required. This study provided hydrological information and an approach that can be used to monitor the hydrological states for better understanding and management of NPRs and catchments.
{"title":"Assessment of the spatiotemporal dynamics of the hydrological state of non-perennial river systems and identification of flow-contributing areas","authors":"Sagwati E Maswanganye, Timothy Dube, Nebo Jovanovic, Evison Kapangaziwiri, Dominic Mazvimavi","doi":"10.17159/wsa/2024.v50.i1.4046","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4046","url":null,"abstract":"Non-perennial rivers (NPRs) have three hydrological states; each state has its importance, function and implication for water resource management. The dynamics of these states have been inadequately assessed and understood. Hence, this study sought to determine the spatiotemporal variations in the hydrological conditions of NPRs, focusing on the Touws River–Karoo drylands and Molototsi River within the semi-arid region of the Limpopo Province of South Africa. Additionally, the study aimed to delineate and characterize the primary areas contributing to runoff in these two river systems. Sentinel-1 and Sentinel-2 satellite data sources were employed in this study. Specifically, the modified normalized difference water index (MNDWI) derived from Sentinel-2 was utilized to delineate water surface areas along the two rivers. Subsequently, these derived datasets were utilized to assess the hydrological states over a 32-month period (2019–2022). Based on the presence of water, the river's state was classified as flowing, pooled, or dry. The results showed that remote sensing can be used to determine the hydrological state of the two river systems with ~90% overall accuracy. However, there is about a 30% chance that a flow event can be missed using Sentinel-2 due to clouds and temporal resolution. Some of these gaps can be filled using synthetic aperture radar (SAR) data (Sentinel-1), as demonstrated with the Molototsi River. In the Molototsi catchment, the upper catchment contributes the majority of flows. For the Touws River, the southwestern part of the catchment was determined as the major contributing area for the observed flows. This suggests that the chosen observation site might not be representative of upper catchment dynamics; therefore, a monitoring site in the upper catchment is required. This study provided hydrological information and an approach that can be used to monitor the hydrological states for better understanding and management of NPRs and catchments.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140481090","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4028
Zhiyuan Zhou, Olubunmi M Olukowi, Yan Xie, Ismaeel O Adebayo, Yuejun Zhang
{"title":"Coagulation efficiency and removal mechanism for composite coagulant polyaluminium chloride/polydimethyldiallylammonium chloride in treating lightly micro-polluted raw water of Yangtze River in autumn","authors":"Zhiyuan Zhou, Olubunmi M Olukowi, Yan Xie, Ismaeel O Adebayo, Yuejun Zhang","doi":"10.17159/wsa/2024.v50.i1.4028","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4028","url":null,"abstract":"","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140481827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4073
M Gomo
Flow Characteristics (FC) is one of the few methods developed for predicting long-term sustainable borehole yield of single wells in typical fractured rock aquifers. The FC method uses drawdown derivatives and subjective information on no-flow boundaries to estimate a sustainable borehole yield that should not cause the water level to drop below the main water strike (fracture) during long-term operations. Since its development, the FC method has been widely applied in many research and consulting projects. Two decades after its development, a review of its technical capabilities and limitations is necessary to enhance understanding among groundwater practitioners while building a platform for further improvements. The main strength of the method is its simplicity of use, its ability to protect the main water strike/fracture, and its lower susceptibility to the influence of aquifer heterogeneities because it does not require the input of aquifer storativity and transmissivity. The FC method also caters to the negative influence of impermeable boundaries, thereby enabling planning for different low-yield-causing scenarios. However, the major limitation is in using the subjective closed no-flow boundary without factoring aquifer storativity and the distance of the closed no-flow boundary from the pumping well. Under the influence of the closed no-flow boundary, the water must come from aquifer storage, hence the storativity and the size of the bounded aquifer are very critical parameters. It is therefore incorrect to factor in the influence of the closed no-flow boundary without considering its exact location. This limitation is reflected in the absence of criteria to determine the distance of the closed no-flow boundary from the pumping well for validating the FC results using numerical models. The FC method still needs validation using field operational data; other recommendations for future research are highlighted in the discussion.
流量特性（FC）是为数不多的几种预测典型裂隙岩含水层中单井长期可持续井眼产水量的方法之一。 FC 方法使用缩减导数和无流边界的主观信息来估算长期作业期间不应导致水位下降到主水流（裂缝）以下的可持续井眼产水量。自开发以来，FC 方法已在许多研究和咨询项目中得到广泛应用。在其发展 20 年之后，有必要对其技术能力和局限性进行审查，以加强地下水从业人员对其的了解，同时为进一步改进建立一个平台。该方法的主要优点是使用简单，能够保护主要水流走向/断裂，而且由于不需要输入含水层的储量和渗透率，因此不易受含水层异质性的影响。FC 方法还能应对不透水边界的负面影响，从而对不同的低产情况进行规划。然而，该方法的主要局限在于使用主观的封闭式无流边界，而没有考虑含水层的储量和封闭式无流边界与抽水井的距离。在封闭式无流量边界的影响下，水量必须来自含水层的储量，因此，含水层的储量和边界含水层的大小是非常关键的参数。 因此，不考虑封闭式无流边界的确切位置而将其影响考虑在内是不正确的。这一局限性体现在缺乏确定封闭式无流边界与抽水井距离的标准，以便利用数值模型验证 FC 结果。FC 方法仍需使用现场运行数据进行验证；讨论中还强调了其他未来研究建议。
{"title":"On the Flow Characteristics (FC) method for estimating sustainable borehole yield","authors":"M Gomo","doi":"10.17159/wsa/2024.v50.i1.4073","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4073","url":null,"abstract":"Flow Characteristics (FC) is one of the few methods developed for predicting long-term sustainable borehole yield of single wells in typical fractured rock aquifers. The FC method uses drawdown derivatives and subjective information on no-flow boundaries to estimate a sustainable borehole yield that should not cause the water level to drop below the main water strike (fracture) during long-term operations. Since its development, the FC method has been widely applied in many research and consulting projects. Two decades after its development, a review of its technical capabilities and limitations is necessary to enhance understanding among groundwater practitioners while building a platform for further improvements. The main strength of the method is its simplicity of use, its ability to protect the main water strike/fracture, and its lower susceptibility to the influence of aquifer heterogeneities because it does not require the input of aquifer storativity and transmissivity. The FC method also caters to the negative influence of impermeable boundaries, thereby enabling planning for different low-yield-causing scenarios. However, the major limitation is in using the subjective closed no-flow boundary without factoring aquifer storativity and the distance of the closed no-flow boundary from the pumping well. Under the influence of the closed no-flow boundary, the water must come from aquifer storage, hence the storativity and the size of the bounded aquifer are very critical parameters. It is therefore incorrect to factor in the influence of the closed no-flow boundary without considering its exact location. This limitation is reflected in the absence of criteria to determine the distance of the closed no-flow boundary from the pumping well for validating the FC results using numerical models. The FC method still needs validation using field operational data; other recommendations for future research are highlighted in the discussion.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140482746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4056
Nkosinathi D Kaptein, Michele L Toucher, Alistair D Clulow, Colin S Everson, Ilaria Germishuizen
We measured the tree transpiration of 9-year-old, Eucalyptus grandis x Eucalyptus urophylla clonal hybrid (GU) trees in the commercial forestry area of northern KwaZulu-Natal, South Africa. Transpiration was measured using the heat ratio method over two consecutive hydrological years (2019/20 and 2020/21) and up-scaled to a stand level. Leaf area index (LAI), quadratic mean diameter, and soil water content (SWC) were measured over the same period using an LAI 2200 plant canopy analyser, manual dendrometers and CS616 sensors, respectively. The depth to groundwater was estimated to be approx. 28 m, using a borehole next to our study site. Results showed that transpiration followed a seasonal pattern, with daily mean of 2.3 mm‧tree−1‧day−1 (range: 0.18 to 4.55 mm‧tree−1‧day−1) and 3.3 mm‧tree−1‧day−1 (range: 0.06 to 6.6 mm‧tree−1‧day−1) for 2019/20 and 2020/21, respectively. Annual GU transpiration was higher than that found by international studies under similar conditions, but was within the same transpiration range as Eucalyptus genotypes in the KwaMbonambi area. Plantation water productivity, calculated as a ratio of stand volume to transpiration, was higher than for other published studies, which was attributed to a very high productive potential of the study site. Multiple regression using the random forests predictive model indicated that solar radiation, SWC and air temperature highly influence transpiration. There is a high possibility that our GU tree rooting system extracted water in the unsaturated zone during the dry season. Due to the use of short-term results in this study, the impact of GU on water resources could not be quantified; however, previous long-term paired catchment studies in South Africa concluded that Eucalyptus has a negative impact on water resources. Further research is suggested with long-term measurements of transpiration and total evaporation and an isotope study to confirm the use of water by GU trees in the unsaturated zone.
我们在南非夸祖鲁-纳塔尔省北部的商业林区测量了树龄为 9 年的大叶桉 x 尤加利树克隆杂交种（GU）的树木蒸腾作用。在连续两个水文年（2019/20 年和 2020/21 年）采用热比法测量蒸腾作用，并将其放大到林分水平。同期分别使用 LAI 2200 植物冠层分析仪、手动测距仪和 CS616 传感器测量了叶面积指数（LAI）、二次平均直径和土壤含水量（SWC）。利用研究地点旁边的一个钻孔，估计地下水深度约为 28 米。结果显示，蒸腾作用具有季节性，2019/20和2020/21年度的日平均蒸腾作用分别为2.3毫米‧树-1‧日-1（范围：0.18至4.55毫米‧树-1‧日-1）和3.3毫米‧树-1‧日-1（范围：0.06至6.6毫米‧树-1‧日-1）。GU的年蒸腾量高于国际研究在类似条件下的蒸腾量，但与KwaMbonambi地区的桉树基因型的蒸腾量在同一范围内。以林分体积与蒸腾量之比计算的种植园水分生产率高于其他已发表的研究，这是因为研究地点的生产潜力非常大。使用随机森林预测模型进行的多元回归表明，太阳辐射、SWC 和气温对蒸腾作用有很大影响。我们的 GU 树生根系统很有可能在旱季抽取了非饱和区的水分。由于本研究使用的是短期结果，因此无法量化桉树对水资源的影响；不过，之前在南非进行的长期配对集水区研究得出结论，桉树对水资源有负面影响。建议开展进一步研究，对蒸腾作用和总蒸发量进行长期测量，并开展同位素研究，以确认桉树在非饱和区的用水情况。
{"title":"Water use and potential hydrological implications of fast-growing Eucalyptus grandis x Eucalyptus urophylla hybrid in northern Zululand, South Africa","authors":"Nkosinathi D Kaptein, Michele L Toucher, Alistair D Clulow, Colin S Everson, Ilaria Germishuizen","doi":"10.17159/wsa/2024.v50.i1.4056","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4056","url":null,"abstract":"We measured the tree transpiration of 9-year-old, Eucalyptus grandis x Eucalyptus urophylla clonal hybrid (GU) trees in the commercial forestry area of northern KwaZulu-Natal, South Africa. Transpiration was measured using the heat ratio method over two consecutive hydrological years (2019/20 and 2020/21) and up-scaled to a stand level. Leaf area index (LAI), quadratic mean diameter, and soil water content (SWC) were measured over the same period using an LAI 2200 plant canopy analyser, manual dendrometers and CS616 sensors, respectively. The depth to groundwater was estimated to be approx. 28 m, using a borehole next to our study site. Results showed that transpiration followed a seasonal pattern, with daily mean of 2.3 mm‧tree−1‧day−1 (range: 0.18 to 4.55 mm‧tree−1‧day−1) and 3.3 mm‧tree−1‧day−1 (range: 0.06 to 6.6 mm‧tree−1‧day−1) for 2019/20 and 2020/21, respectively. Annual GU transpiration was higher than that found by international studies under similar conditions, but was within the same transpiration range as Eucalyptus genotypes in the KwaMbonambi area. Plantation water productivity, calculated as a ratio of stand volume to transpiration, was higher than for other published studies, which was attributed to a very high productive potential of the study site. Multiple regression using the random forests predictive model indicated that solar radiation, SWC and air temperature highly influence transpiration. There is a high possibility that our GU tree rooting system extracted water in the unsaturated zone during the dry season. Due to the use of short-term results in this study, the impact of GU on water resources could not be quantified; however, previous long-term paired catchment studies in South Africa concluded that Eucalyptus has a negative impact on water resources. Further research is suggested with long-term measurements of transpiration and total evaporation and an isotope study to confirm the use of water by GU trees in the unsaturated zone.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140481246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4067
OJ Gericke, JPJ Pietersen, JC Smithers, JA du Plessis
Event-based estimates of the design flood in ungauged catchments are normally based on a single catchment response time parameter expressed as either the time of concentration (TC), lag time (TL) and/or time to peak (TP). In small, gauged catchments, a simplified convolution process between a single observed hyetograph and hydrograph is generally used to estimate these time parameters. In medium to large heterogeneous, gauged catchments, such a simplification is neither practical nor applicable, given that the variable antecedent soil moisture status resulting from previous rainfall events and spatially non-uniform rainfall hyetographs can result in multi-peaked hydrographs. In ungauged catchments, time parameters are estimated using either empirical or hydraulic methods. In South Africa (SA), unfortunately, the majority of the empirical methods recommended for general use were developed and verified in catchments ≤ 0.45 km² without using any local data. This paper presents the further development and verification of the streamflow-based approach developed by Gericke (2016) to estimate observed TP values and to derive a regional empirical TP equation in Primary Drainage Region X, SA. A semi-automated hydrograph analysis tool was developed to extract and analyse complete hydrographs for time parameter estimation using primary streamflow data from 51 flow-gauging sites. The observed TP values were estimated using three methods: (i) duration of total net rise of a multi-peaked hydrograph, (ii) triangular-shaped direct runoff hydrograph approximations, and (iii) linear catchment response functions. The combined use of these methods incorporated the high variability of event-based time parameters, and Method (iii), in conjunction with an ensemble-event approach sampled from the time parameter distributions, should replace the event-based approaches to enable the improved calibration of empirical time parameter equations. The conceptual approach used to derive the regional empirical TP equation should also be adopted when regional equations need to be derived at a national scale in SA.
{"title":"Alternative streamflow-based approach to estimate catchment response time in medium to large catchments: case study in Primary Drainage Region X, South Africa","authors":"OJ Gericke, JPJ Pietersen, JC Smithers, JA du Plessis","doi":"10.17159/wsa/2024.v50.i1.4067","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4067","url":null,"abstract":"Event-based estimates of the design flood in ungauged catchments are normally based on a single catchment response time parameter expressed as either the time of concentration (TC), lag time (TL) and/or time to peak (TP). In small, gauged catchments, a simplified convolution process between a single observed hyetograph and hydrograph is generally used to estimate these time parameters. In medium to large heterogeneous, gauged catchments, such a simplification is neither practical nor applicable, given that the variable antecedent soil moisture status resulting from previous rainfall events and spatially non-uniform rainfall hyetographs can result in multi-peaked hydrographs. In ungauged catchments, time parameters are estimated using either empirical or hydraulic methods. In South Africa (SA), unfortunately, the majority of the empirical methods recommended for general use were developed and verified in catchments ≤ 0.45 km² without using any local data. This paper presents the further development and verification of the streamflow-based approach developed by Gericke (2016) to estimate observed TP values and to derive a regional empirical TP equation in Primary Drainage Region X, SA. A semi-automated hydrograph analysis tool was developed to extract and analyse complete hydrographs for time parameter estimation using primary streamflow data from 51 flow-gauging sites. The observed TP values were estimated using three methods: (i) duration of total net rise of a multi-peaked hydrograph, (ii) triangular-shaped direct runoff hydrograph approximations, and (iii) linear catchment response functions. The combined use of these methods incorporated the high variability of event-based time parameters, and Method (iii), in conjunction with an ensemble-event approach sampled from the time parameter distributions, should replace the event-based approaches to enable the improved calibration of empirical time parameter equations. The conceptual approach used to derive the regional empirical TP equation should also be adopted when regional equations need to be derived at a national scale in SA.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140483156","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4053
M Baderoon, K Winter
Rainfall has been shown to be the main cause of elevated nutrient pollution in groundwater beneath landfills. However, groundwater monitoring is often based on predetermined schedules without considering rainfall patterns. This study examined how rainfall patterns affect fluctuations in groundwater quality at the Coastal Park landfill in Cape Town, South Africa, and the relevance of current groundwater sampling schedules. Boreholes upstream and downstream of two large waste cells, one lined and the other unlined, were monitored for 15 weeks during the onset of the rainy season to detect changes in the groundwater level, pH, conductivity, dissolved oxygen, ammonia, nitrate, and phosphate. Rainfall patterns strongly affected the groundwater parameters, with widely varying fluctuation patterns and lag times. Conductivity peaked downstream of the lined cell 10 weeks later than at the unlined cell, with widely different fluctuation patterns (R2 = 0.36). Ammonia peaked downstream of both the unlined and lined cells well before the early rains, with very similar fluctuation patterns (R2 = 0.97), although it peaked 6 times higher in the unlined cell. Nitrate peaked at Weeks 2 to 4 downstream of the unlined and the lined cell, with a weak correlation (R2 = 0.56). A shorter nitrate peak and a net decrease throughout the rainy season were observed downstream of the lined cell. Phosphate showed a brief, multi-fold increase at Week 3 downstream of both the unlined and lined cells, displaying pH-induced mobilisation and a very strong correlation (R2 = 0.99) between these locations. Lag times and fluctuation patterns varied depending on the presence of liners, and rainfall patterns. Therefore, the low frequency sampling required by many South African landfill waste management permits and licences cannot identify pollutant peak concentrations or describe their trends, and high frequency sampling should be considered.
{"title":"Groundwater contaminant fluctuation at a landfill: a case study of the Coastal Park Landfill, Cape Town","authors":"M Baderoon, K Winter","doi":"10.17159/wsa/2024.v50.i1.4053","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4053","url":null,"abstract":"Rainfall has been shown to be the main cause of elevated nutrient pollution in groundwater beneath landfills. However, groundwater monitoring is often based on predetermined schedules without considering rainfall patterns. This study examined how rainfall patterns affect fluctuations in groundwater quality at the Coastal Park landfill in Cape Town, South Africa, and the relevance of current groundwater sampling schedules. Boreholes upstream and downstream of two large waste cells, one lined and the other unlined, were monitored for 15 weeks during the onset of the rainy season to detect changes in the groundwater level, pH, conductivity, dissolved oxygen, ammonia, nitrate, and phosphate. Rainfall patterns strongly affected the groundwater parameters, with widely varying fluctuation patterns and lag times. Conductivity peaked downstream of the lined cell 10 weeks later than at the unlined cell, with widely different fluctuation patterns (R2 = 0.36). Ammonia peaked downstream of both the unlined and lined cells well before the early rains, with very similar fluctuation patterns (R2 = 0.97), although it peaked 6 times higher in the unlined cell. Nitrate peaked at Weeks 2 to 4 downstream of the unlined and the lined cell, with a weak correlation (R2 = 0.56). A shorter nitrate peak and a net decrease throughout the rainy season were observed downstream of the lined cell. Phosphate showed a brief, multi-fold increase at Week 3 downstream of both the unlined and lined cells, displaying pH-induced mobilisation and a very strong correlation (R2 = 0.99) between these locations. Lag times and fluctuation patterns varied depending on the presence of liners, and rainfall patterns. Therefore, the low frequency sampling required by many South African landfill waste management permits and licences cannot identify pollutant peak concentrations or describe their trends, and high frequency sampling should be considered.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140482083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4064
Enes Gül, Zeyneb Kılıç, Erdinç İkincioğulları, M Cihan Aydın
The present research used a combination of experimental and numerical methods to investigate energy dissipation blocks of different heights placed downstream of a sluice gate in an open channel flow. Numerical model simulations were performed using a 3D computational fluid dynamics (CFD) technique, using the Reynolds-averaged Navier-Stokes (RANS) equations with the volume of fluid (VOF) and k-ε turbulence models. The accuracy of the numerical model and the grid sensitivity was assessed according to a recommended procedure in the literature. Different hydraulic and geometry conditions were investigated to understand the energy dissipation behaviour of the blocks. The hydrodynamic effects of different block spacings, heights and configurations were analysed by means of CFD simulations. The results show that the variable size blocks have a high energy dissipation efficiency in sluice gate flows, particularly at high Froude numbers. The energy dissipation efficiency of the blocks downstream of a sluice gate can reach up to 55% for high discharges (Q = 35 L/s). Interestingly, the energy dissipation performance of small gate openings exceeds that of large gate openings, reaching a peak efficiency of 40% for the same discharge. In addition, the block spacing has a minimal effect on the energy dissipation, while smaller block spacing results in a smoother water surface profile.
{"title":"Investigation of the effect of variable-sized energy dissipating blocks on sluice gate performance","authors":"Enes Gül, Zeyneb Kılıç, Erdinç İkincioğulları, M Cihan Aydın","doi":"10.17159/wsa/2024.v50.i1.4064","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4064","url":null,"abstract":"The present research used a combination of experimental and numerical methods to investigate energy dissipation blocks of different heights placed downstream of a sluice gate in an open channel flow. Numerical model simulations were performed using a 3D computational fluid dynamics (CFD) technique, using the Reynolds-averaged Navier-Stokes (RANS) equations with the volume of fluid (VOF) and k-ε turbulence models. The accuracy of the numerical model and the grid sensitivity was assessed according to a recommended procedure in the literature. Different hydraulic and geometry conditions were investigated to understand the energy dissipation behaviour of the blocks. The hydrodynamic effects of different block spacings, heights and configurations were analysed by means of CFD simulations. The results show that the variable size blocks have a high energy dissipation efficiency in sluice gate flows, particularly at high Froude numbers. The energy dissipation efficiency of the blocks downstream of a sluice gate can reach up to 55% for high discharges (Q = 35 L/s). Interestingly, the energy dissipation performance of small gate openings exceeds that of large gate openings, reaching a peak efficiency of 40% for the same discharge. In addition, the block spacing has a minimal effect on the energy dissipation, while smaller block spacing results in a smoother water surface profile.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140485227","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4040
Aldré Nel, DE Bosman, Gr Basson
This study quantified transfer losses over the 2021/2022 water year for irrigation releases from Darlington Dam into the Sundays River, which are diverted at the Korhaans Drift Weir. A one-dimensional (1D) hydrodynamic model was set up and calibrated to simulate the transfer losses which were assumed to consist primarily of evaporation and evapotranspiration (ET). Flow measurements were undertaken with an acoustic doppler current profiler (ADCP) to verify the calibrations of the Parshall flumes at Darlington Dam and at Korhaans Drift Weir. The ADCP results showed that the Department of Water and Sanitation’s (DWS’s) existing discharge tables underestimated lower flows by 13% and higher flows by 16%. The hydrodynamic model results also estimated transfer losses between Darlington Dam and Korhaans Drift to range between 2.0% and 5.3%. It was determined that the transfer losses were seasonal and were lower than those determined by similar studies for other South African rivers.
{"title":"Utilization of hydrodynamic modelling to quantify water losses from the Sundays River between Darlington Dam and Korhaans Drift Weir","authors":"Aldré Nel, DE Bosman, Gr Basson","doi":"10.17159/wsa/2024.v50.i1.4040","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4040","url":null,"abstract":"This study quantified transfer losses over the 2021/2022 water year for irrigation releases from Darlington Dam into the Sundays River, which are diverted at the Korhaans Drift Weir. A one-dimensional (1D) hydrodynamic model was set up and calibrated to simulate the transfer losses which were assumed to consist primarily of evaporation and evapotranspiration (ET). Flow measurements were undertaken with an acoustic doppler current profiler (ADCP) to verify the calibrations of the Parshall flumes at Darlington Dam and at Korhaans Drift Weir. The ADCP results showed that the Department of Water and Sanitation’s (DWS’s) existing discharge tables underestimated lower flows by 13% and higher flows by 16%. The hydrodynamic model results also estimated transfer losses between Darlington Dam and Korhaans Drift to range between 2.0% and 5.3%. It was determined that the transfer losses were seasonal and were lower than those determined by similar studies for other South African rivers.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140484441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.17159/wsa/2024.v50.i1.4022
D van der Spuy, JA du Plessis
The performance of the most frequently used flood frequency probability distributions in South Africa (Log-Normal, Log Pearson3 and Generalised Extreme Value) were reviewed and all tend to perform poorly when lower exceedance probability frequency events are estimated, especially where outliers are present in the dataset. This can be attributed to the challenge when analysing very limited ‘samples’ of annual flood peak populations, which are an unknown. At present outliers are inadequately 'managed' by attempting to 'normalise' the flood peak dataset, which conceals the significance of the observed data. Thus, to adequately consider the outliers, this study was undertaken with the aim to improve the current statistical approach by developing a more stable and consistent methodology to estimate flood quantiles. The approach followed in the development of the new methodology, called IPZA, might be considered as unconventional, given that a multiple regression approach was used to accommodate the strongly skewed data, which are often associated with annual flood peak series. The main advantages of IPZA are consistency, the simplicity of application (only one set of frequency factors for every parameter, regardless of the skewness), the integrated handling of outliers and the use of conventional method of moments, thereby eliminating the need to adjust any moments. The performance of IPZA exceeded initial expectations. The results are more consistent and, by taking outliers into account, appear to be more sensible than existing probability distributions. It is recommended that IPZA should be used as a valuable addition to the existing set of decision-making tools for hydrologists/engineers performing flood frequency analyses.
{"title":"Improved flood quantile estimation for South Africa","authors":"D van der Spuy, JA du Plessis","doi":"10.17159/wsa/2024.v50.i1.4022","DOIUrl":"https://doi.org/10.17159/wsa/2024.v50.i1.4022","url":null,"abstract":"The performance of the most frequently used flood frequency probability distributions in South Africa (Log-Normal, Log Pearson3 and Generalised Extreme Value) were reviewed and all tend to perform poorly when lower exceedance probability frequency events are estimated, especially where outliers are present in the dataset. This can be attributed to the challenge when analysing very limited ‘samples’ of annual flood peak populations, which are an unknown. At present outliers are inadequately 'managed' by attempting to 'normalise' the flood peak dataset, which conceals the significance of the observed data. Thus, to adequately consider the outliers, this study was undertaken with the aim to improve the current statistical approach by developing a more stable and consistent methodology to estimate flood quantiles. The approach followed in the development of the new methodology, called IPZA, might be considered as unconventional, given that a multiple regression approach was used to accommodate the strongly skewed data, which are often associated with annual flood peak series. The main advantages of IPZA are consistency, the simplicity of application (only one set of frequency factors for every parameter, regardless of the skewness), the integrated handling of outliers and the use of conventional method of moments, thereby eliminating the need to adjust any moments. The performance of IPZA exceeded initial expectations. The results are more consistent and, by taking outliers into account, appear to be more sensible than existing probability distributions. It is recommended that IPZA should be used as a valuable addition to the existing set of decision-making tools for hydrologists/engineers performing flood frequency analyses.","PeriodicalId":23623,"journal":{"name":"Water SA","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140485493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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