Nasr, Ahmed Elssidig
Nasr, Ahmed Elssidig
Nasr, Ahmed Elssidig
Now showing 1 - 10 of 18
- PublicationDeveloping an independent, generic, phosphorus modelling component for use with grid-oriented, physically-based distributed catchment modelsGrid-oriented, physically based catchment models calculate fields of various hydrological variables relevant to phosphorous detachment and transport. These include (i) for surface transport: overland flow depth and flow in the coordinate directions, sediment load, and sediment concentration and (ii) for subsurface transport: soil moisture and hydraulic head at various depths in the soil. These variables can be considered as decoupled from any chemical phosphorous model since phosphorous concentrations, either as dissolved or particulate, do not influence the model calculations of the hydrological fields. Thus the phosphorous concentration calculations can be carried out independently from and after the hydrological calculations. This makes it possible to produce a separate phosphorous modelling component which takes as input the hydrological fields produced by the catchment model and which calculates, at each step the phosphorous concentrations in the flows. This paper summarise the equations and structure of Grid Oriented Phosphorous Component (GOPC) developed for simulating the phosphorus concentrations and loads using the outputs of a fully distributed physical based hydrological model. Also the GOPC performance is illustrated by am example of an experimental catchment (created by the author) subjected to some ideal conditions.
- PublicationComparison of different forms of the multi-layer feed-forward neural network method used for river flow forecast combinationThe multi-layer feed-forward neural network (MLFFNN) is applied in the context of river flow forecast combination, where a number of rainfall-runoff models are used simultaneously to produce an overall combined river flow forecast. The operation of the MLFFNN depends on the neuron transfer function, which is non-linear. These models, each having a different structure to simulate the perceived mechanisms of the runoff process, utilise the information carrying capacity of the model calibration data indifferent ways. Hence, in a discharge forecast combination procedure, the discharge forecasts of each model provide a source of information different from that of the other models used in the combination. In the present work, the significance of the choice of the transfer function type in the overall performance of the MLFFNN, when used in the river flow forecast combination context is critically investigated. Five neuron transfer functions are used in this investigation, namely, the logistic function, the bipolar function, the hyperbolic function, the arctan function and the scaled arctan function. The results indicate that the logistic function yields the best model forecast combination performance.
- PublicationComparison of physically based catchment models for estimating Phosphorus lossesAs part of a large EPA-funded research project, coordinated by TEAGASC, the Centre for Water Resources Research at UCD reviewed the available distributed physically based catchment models with a potential for use in estimating phosphorous losses for use in implementing the Water Framework Directive. Three models, representative of different levels of approach and complexity, were chosen and were implemented for a number of Irish catchments. This paper reports on (i) the lessons and experience gained in implementing these models, (ii) compares the performances of the individual models and (iii) assesses their sensitivities to the main parameters and to spatial scales.
- PublicationThe significance of the differences in soil phosphorus representation and transport procedures in the SWAT and HSPF models and a comparison of their performance in estimating phosphorus loss from an agriculture catchment in IrelandPhosphorus transported from agriculture land has been identified as a major source of water pollution in a large number of Irish catchments. Models of this process are required in order to design and assess management measures. This paper reports on the comparison and assessment of two of the most promising physically-based distributed models, SWAT and HSPF, with particular emphasis on their suitability for Irish conditions. The representation of the overall soil phosphorus cycle is similar in both models but there is a significant difference in the level of detail in describing the chemical and biochemical processes in each model. Also there are differences in modeling the mechanisms by which phosphorus is removed from the soil column and either transported in dissolved form with the runoff water or in particulate form attached to eroded or detached sediment. These differences could have a significant influence on performance when using either of the models to simulate phosphorus loss from any catchment. Both models are applied to estimating the phosphorus concentration at the outlet of the Clarianna catchment in north Tiperrary (Ireland). This catchment is small (23km2) and the landuse is mainly pasture on grey brown podozilic soils. The results of model calibration are presented along with an assessment of the usefulness of the model outputs as a water quality management tool.
- PublicationPhysically-based, distributed, catchment modelling for estimating sediment and phosphorus loads to rivers and lakes : issues of model complexity, spatial and temporal scales and data requirements
- PublicationCoupling system model with fuzzy logic rules for use in runoff and total phosphorus load prediction in a catchmentTackling the problem of eutrophication in fresh waters is at the top of the agenda for the implementation of the Water Framework Directive (WFD) in Europe. The problem is caused primarily by an increase in phosphorus loading from diffuse sources. Therefore there is a need to apply appropriate measures, which are able to reduce the phosphorus diffuse pollution, at a catchment scale in each River Basin District (RBD). As the implementation of such measures disturbs the existing system in the catchment it is important to be able to predict their impact and this requires a reliable mathematical model to represent the system. In this study, a new, lumped catchment, methodology to improve on an existing diffuse phosphorus pollution model, the Grid Oriented Phosphorus Component (GOPC) model, is proposed. This methodology consists of two elements; (i) the Soil Moisture Accounting and Routing (SMAR) hydrological model was used to provide the required hydrological variables to the GOPC model; and (ii) fuzzy logic rules were formulated with the notion that each rule corresponds to a sub-model representing a particular hydrological behaviour in the catchment and the combined results of all rules give the total response. Sixteen modelling cases, each of which uses different numbers of fuzzy sub-sets for the rainfall and the evaporation, were compared for their discharge and total phosphorus (TP) simulations in a catchment in Northern Ireland. The comparison was based on the validation results as they allow testing the applicability of the models for conditions different from those used in the calibration period. Using 2 fuzzy sub-sets for the rainfall and a single fuzzy sub-set for the evaporation produced the best simulation for the discharge whereas the best TP simulation was obtained from the case of 4 rainfall fuzzy sub-sets and 3 evaporation fuzzy sub-sets.
- PublicationEstimating the parameters of the extreme value type 1 distribution for low flow series in IrelandIn this study two different models have been developed and tested with data from 55 hydrometric stations in the Shannon River Basin in Ireland for estimating the location and the scale parameters of the EV1 distribution of the Minimum, 3-, 7-, 10-, 15-, and 30-days sustained low flow series at ungauged locations. The first is a simple linear model while the other is a fuzzy clustering model. Both models have been calibrated using the unconstrained and the constrained least squares methods. Moreover five different input scenarios including various combinations of some explanatory variables have been investigated with the two models. The results showed that: (i) the simple linear model calibrated by the constrained least squares method was the best model to estimate the EV1 location parameter using catchment area, mean annual rainfall, mean elevation, mean slope, and soil as explanatory variables, and (ii) the fuzzy clustering model calibrated by the unconstrained least squares method was the best for the EV1 scale parameter using only the first four above mentioned explanatory variables.
- PublicationMulti-criteria and Decision Support Systems in support of the Water Framework Directive in IrelandThe current challenge in the implementation of the Water Framework Directive in Ireland is to introduce programmes of measures that will address the targeted environmental objectives in each River Basin District (RBD). Introduction of such programmes requires that proposed measures be thoroughly evaluated and that decisions will involve multiple criteria and must include stakeholders preferences and opinions. Decision Support Systems (DSS) facilitate this process. Many such systems have been developed and used in relation to water quality. In addition to their technical, modeling, benefits, DSS can also form the basis of systems to communicate options, benefits and damages to stakeholders and to receive feedback on their attitudes and preferences. Such systems could also be involved in facilitating the subsequent negotiations and resulting compromises. In Ireland, a new research project, Wincoms, has commenced which will address these aspects and will provide recommendations for suitable systems to be used in Ireland.
- PublicationEutrophication from agricultural sources : a comparison of SWAT, HSPF and SHETRAN/GOPC phosphorus models for three Irish catchments - Final ReportPhosphorous has been implicated as the primary cause of the deterioration of surface water quality in Ireland. Extensive water quality surveys revealed that diffuse sources (runoff and subsurface flows) from agricultural land are the major contributors of phosphorus to surface waters. The mechanism of phosphorus movement from land to water can be described by a number of mathematical models that vary in modelling approaches and scales (plot, field and catchment). In this work three efficient mathematical models of diffuse source pollution in general and of phosphorus in particular have been applied, for the first time, to three Irish catchments (Clarianna (Co. Tipperary), Dripsey (Co. Cork) and Oona (Co. Tyrone)) in order to explore the suitability of these models in Irish conditions for future use in implementing the European Water Framework Directive (WFD). The models are: (i) Soil Water Assessment Tool (SWAT), (ii) Hydrological Simulation Programme FORTRAN (HSPF) and (iii) Système Hydrologique Européen TRAnsport (SHETRAN). The first two can model phosphorus production directly while the third can calculate fields of various hydrological variables relevant to phosphorous modelling. For the latter, a generic phosphorus modelling component called Grid Oriented Phosphorus Component (GOPC) has been developed here to model the phosphorus detachment and transport by taking as inputs the hydrological fields produced by any physically-based distributed catchment model such as SHETRAN. The three models have been successfully transferred to Irish conditions and this required the build up of a database consisting of topographic, land use and soil maps, water quality and weather data. The models application involved two stages. In the first stage, hydrological variables (evaporation, runoff, etc.) within the catchment domains were simulated by each of the three models. The second stage uses the outputs of the first in order to estimate the amount of phosphorus loss from the catchments. The SWAT, HSPF, and SHETRAN/GOPC models have been calibrated and then compared and assessed on the basis of their ability to fit and reproduce the flow discharges and phosphorus loads and concentrations for the three test catchments. The findings from the flow and phosphorus calibrations of SWAT and HSPF models were generally consistence with what have been found from previous studies outside Ireland. However, the simple structure of the first order kinetics method used for phosphorus modelling in HSPF has generally impeded the freedom of the phosphorus calibration which was noticeably difficult. Application of the SHETRAN model to the study catchments has illustrated the importance of carefully assigning the parameters related to the soil water modelling, particularly the parameters of the van Genuchten soil-hydraulic function, in order to obtain the best results. The GOPC performance has been found to depend significantly on the SHETRAN model which provided the required hydrological variables. The flow comparison has showed that in the three catchments, the HSPF model was the best in simulating the mean daily discharges. Moreover discharge simulation from an independent validation run of the three models in the Oona catchment have also demonstrated the superiority of the hydrological component of HSPF. However, the best calibration results for daily total phosphorus loads in the study catchments has been achieved by the SWAT model. However from the validation in the Oona catchment the HSPF has been found better than the other two models, SWAT and GOPC, in simulating the total phosphorus loads. Generally the results of total phosphorus loads from the GOPC in the three catchments were quite good and this model has reproduced some observed values better than the best model, SWAT. Simulation of the daily dissolved reactive phosphorus loads by the three models in the study catchments have showed big differences between the simulated and the observed data in most of the cases. Results for mean daily total and dissolved reactive phosphorus concentrations from the three models were not as good as the results for the loads in the three catchments.
- PublicationAssessment of factors affecting flood forecasting accuracy and reliability. Carpe Diem Centre for Water Resources Research : Deliverable 10.3In Deliverable 10.1, a optimal methodology for combining precipitation information from raingauges, radar and NWP models (in this case HIRLAM) was described. It was based on an artificial neural network combination model, fitted to historic data, and operating on one-dimensional time-series of discharges. In this report, this new methodology is tested by applying it to (i) a rural catchment (Dargle)and (ii) a small urban catchment (CityWest). The results are compared with measured discharge series in both cases. Various measures of performance, applied to both the entire discharge series and also to the peaks-only are reported for various combinations of lead-time, spatial resolution and numbers of neurons in the hidden layer of the ANN model.