A method to disaggregate monthly flows to daily using daily rainfall observations: model design and testing

Slaughter, Andrew; Retief, D.C.H.; Hughes, Denis A.

doi:10.1080/02626667.2014.993987

Cited by 10 publications

(7 citation statements)

References 24 publications

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“…The approaches used and the validity of the WQSAM model have been validated in previous studies, including the monthly-to-daily flow disaggregation (Slaughter et al, 2015;Hughes and Slaughter, 2016) and the water quality modelling processes Slaughter, 2017), which include simulations of salinity as total dissolved solids (TDS), nutrients (nitrates plus nitrites, phosphates and ammonia) and microbial water quality, illustrating that the approach adopted by WQSAM is appropriate for modelling water quality in South Africa under conditions of limited observed data and management capacity.…”

Section: Introductionmentioning

confidence: 90%

“…Gorgens and de Clercq, 2006;Piesold et al, 2007), the adoption of a routinely-used water quality model within management agencies in South Africa has been hampered by the lack of observed data with which to calibrate these models and insufficient technical expertise to accurately set up these models. This led to the development of the Water Quality Systems Assessment Model (Slaughter et al, , 2015Hughes and Slaughter, 2016;Slaughter, 2017;Slaughter and Mantel, 2017a), which specifically links to the routinely-used systems models in South Africa, namely the WRYM and WReMP models, and subscribes to an approach of requisite simplicity (Stirzaker et al, 2010) by only representing processes that explain the majority of variation of observed water quality data.…”

Section: Introductionmentioning

confidence: 99%

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Water quality modelling of an impacted semi-arid catchment using flow data from the WEAP model

Slaughter

Mantel

2018

Proc. IAHS

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Abstract. The continuous decline in water quality in many regions is forcing a shift from quantity-based water resources management to a greater emphasis on water quality management. Water quality models can act as invaluable tools as they facilitate a conceptual understanding of processes affecting water quality and can be used to investigate the water quality consequences of management scenarios. In South Africa, the Water Quality Systems Assessment Model (WQSAM) was developed as a management-focussed water quality model that is relatively simple to be able to utilise the small amount of available observed data. Importantly, WQSAM explicitly links to systems (yield) models routinely used in water resources management in South Africa by using their flow output to drive water quality simulations. Although WQSAM has been shown to be able to represent the variability of water quality in South African rivers, its focus on management from a South African perspective limits its use to within southern African regions for which specific systems model setups exist. Facilitating the use of WQSAM within catchments outside of southern Africa and within catchments for which these systems model setups to not exist would require WQSAM to be able to link to a simple-to-use and internationally-applied systems model. One such systems model is the Water Evaluation and Planning (WEAP) model, which incorporates a rainfall-runoff component (natural hydrology), and reservoir storage, return flows and abstractions (systems modelling), but within which water quality modelling facilities are rudimentary. The aims of the current study were therefore to: (1) adapt the WQSAM model to be able to use as input the flow outputs of the WEAP model and; (2) provide an initial assessment of how successful this linkage was by application of the WEAP and WQSAM models to the Buffalo River for historical conditions; a small, semi-arid and impacted catchment in the Eastern Cape of South Africa. The simulations of the two models were compared to the available observed data, with the initial focus within WQSAM on a simulation of instream total dissolved solids (TDS) and nutrient concentrations. The WEAP model was able to adequately simulate flow in the Buffalo River catchment, with consideration of human inputs and outputs. WQSAM was adapted to successfully take as input the flow output of the WEAP model, and the simulations of nutrients by WQSAM provided a good representation of the variability of observed nutrient concentrations in the catchment. This study showed that the WQSAM model is able to accept flow inputs from the WEAP model, and that this approach is able to provide satisfactory estimates of both flow and water quality for a small, semi-arid and impacted catchment. It is hoped that this research will encourage the application of WQSAM to an increased number of catchments within southern Africa and beyond.

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Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Water quality modelling of an impacted semi-arid catchment using flow data from the WEAP model

Slaughter

Mantel

2018

Proc. IAHS

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“…Sub daily rainfall is seldom available to modellers; pragmatically SASYM needs to run on a daily time step if processes are to be effectively simulated. Inputs to the Pitman model are daily rainfall but as the conventional model runs on a monthly time step the generated flows must be disaggregated to daily using a monthly-daily flow disaggregation method [39].…”

Section: Runoff Modelling and Catchment Zonesmentioning

confidence: 99%

“…Daily flows (m 3 s −1 ) are required for the erosion estimation. These can either be an unbroken time series of observed daily flow, daily flow estimated from a daily hydrological model such as the Agricultural Catchments Research Unit (ACRU) model [17], or monthly flow simulated from a monthly hydrological model such as the Pitman Model [38] disaggregated to daily using a monthly to daily disaggregation routine (e.g., [39]).…”

Section: Fundingmentioning

confidence: 99%

Integrating Sediment (dis)Connectivity into a Sediment Yield Model for Semi-Arid Catchments

Lodenkemper

Rowntree

Hughes

et al. 2021

Land

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Soil erosion-associated sedimentation has become a significant global threat to sustainable land and water resources management. Semi-arid regions that characterise much of southern Africa are particularly at risk due to extreme hydrological regimes and sparse vegetative cover. This study aims to address the need for an erosion and sediment delivery model that successfully incorporates our conceptual understanding of sedimentation processes in semi-arid regions, particularly sediment storage and connectivity within a catchment. Priorities of the Semi-arid Sediment Yield Model (SASYM) were simplicity and practical applicability for land and water resource management while adhering to basic geomorphic and hydrological principles. SASYM was able to represent multiple sediment storages within a catchment to effectively represent a change in landscape connectivity over geomorphic timeframes. SASYM used the Pitman rainfall–runoff model disaggregated to a daily timescale, the Modified Universal Soil Loss Equation (MUSLE), incorporating probability function theory and a representation of sediment storages and connectors across a semi-distributed catchment. SASYM was applied to a catchment in the Karoo, South Africa. Although there were limited observed data, there was a historical dataset available for the catchment through dam sedimentation history. SASYM was able to effectively present this history and provide evidence for landscape connectivity change.

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“…The application of existing internationally developed water quality models to South African catchments is hindered by the aforementioned constraints on observed data and modelling expertise. Within this context, the Water Quality Systems Assessment Model (WQSAM) (Hughes and Slaughter, 2016;Slaughter et al, 2015) was designed to use the available observed water quality data and to simulate water quality data that are useful for water resource management in South Africa, in that WQSAM takes as input, flow data generated by routinely used systems models, and water quality data are simulated in a form that is able to provide an estimate of risks associated with management decisions. WQSAM has initially focused on simulating nutrients, as eutrophication is arguably currently the most pressing water quality issue within freshwater resources in South Africa.…”

Section: Introductionmentioning

confidence: 99%

Land cover models to predict non-point nutrient inputs for selected biomes in South Africa

Slaughter

Mantel

2017

WSA

Self Cite

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WQSAM is a practical water quality model for use in guiding southern African water quality management. However, the estimation of non-point nutrient inputs within WQSAM is uncertain, as it is achieved through a combination of calibration and expert knowledge. Non-point source loads can be correlated to particular land cover types. Although observed water quality data through which non-point source loads can be estimated are scarce, land cover databases exist covering the entire area of South Africa. To reduce the uncertainty associated with estimating non-point source loads, this study describes a formal model to link the nutrient signatures of incremental flow to land cover. Study catchments incorporating the fynbos, grassland, savanna and thicket biomes were identified. Instream nutrients of 25 sites were modelled using WQSAM and calibrated against observed data. Multiple regression was used to investigate the relationships between the calibrated nutrient signatures of incremental flow from WQSAM and land cover within study sites. The regression models reflected greater non-point loads from cultivation-and urban-related land cover categories. The nutrient signatures of incremental flow obtained through the multiple regressions were consistent with those obtained through calibration of the WQSAM model at higher signature values, whereas discrepancies were evident at lower values. It is argued that this formal modelling approach for linking land cover to nutrient signatures of incremental flow can be implemented for situations where it is known that there are strong non-point inputs of nutrients into a river reach. The statistical model presented in the current study could potentially be applied as an alternative to the water quality model as a relatively simple method to estimate non-point source loads of nutrients from tributary catchments in South Africa.

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A method to disaggregate monthly flows to daily using daily rainfall observations: model design and testing

Cited by 10 publications

References 24 publications

Water quality modelling of an impacted semi-arid catchment using flow data from the WEAP model

Water quality modelling of an impacted semi-arid catchment using flow data from the WEAP model

Integrating Sediment (dis)Connectivity into a Sediment Yield Model for Semi-Arid Catchments

Land cover models to predict non-point nutrient inputs for selected biomes in South Africa

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