Conceptual rainfall runoff (CRR) models usually require calibration to identify their parameter values, whereas their model structure is selected prior to modelling. Consid- erable efforts have been directed into calibration of lumped CRR models. Identification of the model structure on the basis of available data still remains unclear. The data-based mechanistic (DBM) approach does minimal assumptions of the model structure, which is identified using powerful statistic techniques. Moreover, there is a similarity between the CRR and DBM model.formulations. Based on this similarity, an integration of CRR and DBM models is proposed and evaluated. Two calibration strategies are investigated in the Upper Illinois river catchment (USA) for lumped modelling. Results show that the identi- fied TF model improves the simulated flow, especially in the time to peak, in comparison to the modelled flow of the conceptual model. It is suggested that this improvement is di- rectly related to the lag time parameter considered in the TF model between the effective rainfall and the flow. Semi-distributed rainfall runoff models provide advantages over lumped models in representing the effect of spatially variable inputs, outputs and catchment properties. However they are affected by parameter identifiability. Four calibration strategies are considered to analyse the ability to meaningful simulate flow at interior locations. Results show that there are no significant improvements at the catchment outlet when internal gauges are included. The behavioural parameter sets defined at the catchment outlet tend to be non-behavioural at the internal gauges. This tendency increases with the distance from the catchment outlet to the internal gauges. Considering only spatial variability of rainfall rather than also of parameter values did not improve the simulations at the out- let or at the internal gauges, compared to lumped modelling results. Calibration only at the catchment outlet using independent sampling of the internal subcatchments achieved similar results. Identification of lumped and semi-distributed CRR models is carried out using the RRTMSD modelling toolbox developed for this work.

The processes relating to runoff generation in a semi-arid environment at the hillslope scale are poorly understood. This research considers the amount and origin of water reaching the channel during a storm event using a combination of field experiments and computer simulation techniques. From the field experiments, it was found that the key controls on runoff generation at the point scale are the surface cover of rock fragments, vegetation cover, slope gradient and surface roughness. The effect of land management was found to be greater than geology. The simulation modelling work investigated the controls on runoff generation at the hillslope and small catchment scales. It was found that the storm characteristics are far more important than surface properties in determining the amount of discharge from a slope. The temporal fragmentation of the rainfall was found to control the distribution of flow path lengths and hence the amount of discharge leaving a slope. The key surface controls on the form of the discharge hydrograph are slope length, slope gradient and the hydrological properties at the base of the slope. The origin of runoff was investigated using autonomous software agents able to trace the flow of water through a catchment. This technique is able to give a unique picture of the origin of runoff within a catchment. It was shown that the spatial pattern of the origin of runoff is complex and varies significantly between catchments. This research has shown that there are two key themes in determining the amount of runoff reaching the channel network: the interplay between the distribution of flow path lengths generated during a storm and the distributions of flow lengths to the channel as a function of the landscape. The second theme relates to the importance of the spatial structure of hydrological areas within the landscape.

Hydrological models are powerful tools for the investigation of many hydrological issues. The historical approach for the development of rainfall-runoff models, with regard to the choice of model structure and the calibration of the free parameters, has been to focus on gauged catchments where sufficient data, in particular stream flow data, are available. Applications of models were then extended to the case of ungauged catchments. In recent years, it has become apparent that this approach did not lead to satisfying results in ungauged catchments, and that the main focus should instead be on ungauged catchments for the implementation of new modelling strategies. This thesis demonstrates the potential of a new conceptual, catchment-scale, semi-distributed, integrated rainfall-runoff model as a modelling tool in both ungauged and gauged catchments for the assessment of water resources management, land use change or climate changes at the catchment scale. The review of existing model structures and regionalisation methods has lead to the development of the Catchment Resources and Soil Hydrology (CRASH) model following the top-down modelling strategy. The free parameters of the model are directly related to controlling factors of the hydrological processes in the United Kingdom, i.e. soil and land use. The classification of the soils according to their hydrological behaviour is based on the Hydrology Of Soil Types (HOST) system. CRASH also incorporates a novel rainfall disaggregation scheme for the derivation of infiltration excess surface runoff. A regional set of model parameters has been derived from the calibration of CRASH in 32 catchments throughout England and Wales covering contrasting climatic, soil, geological, and land use conditions. The single-site and regional CRASH models performed satisfactorily according to reviewed performance criteria for gauged catchments and to a scoring system proposed for ungauged catchments. However the quality of stream flow data in the UK which was used for the calculation of the regional parameter set, in particular the widespread unavailability of naturalised flow data, tends to limit the performance of the regional CRASH model for low flows.

Rainfall-runoff models are indispensable tools in most hydrological studies. However, the identification of appropriate models remains a difficult problem despite decades of research. This dissertation analyses the identification of conceptual, parsimonious (which may be best translated as parameter efficient), lumped continuous models for gauged and ungauged catchments. The emphasis of this study lies on review and development of new methodologies, not so much on extensive applications. Though different investigative examples of how these new approaches can be applied are shown and a limited case study is provided. A modelling toolkit has been developed after an extensive review of current model structures and modelling procedures. It consists of two components, a Rainfall-Runoff Modelling (RRMT) and a Monte Carlo Analysis Toolbox (MGAT). These allow for the quick implementation and evaluation of rainfall-runoff model structures, although the latter has much more general applicability. The review of local modelling procedures, i.e. applicable to gauged catchments, has lead to the analysis and further development of multi-objective procedures for model performance and identifiability analysis. A novel DYNamic Identifiability Analysis (DYNIA) methodology has been developed which, amongst other things, can be used to analyse inadequacies in a model structure. Both approaches are combined in a framework of corroboration and rejection which can be applied to any dynamic mathematical model structure. This local procedure is extended to the regional case, i.e. applicable to ungauged catchments. Regional information about model parameters is used to derive statistical relationships with catchment characteristics. Various approaches are discussed and analysed. The most promising techniques, combined with new ways of considering uncertainty in the regional modelling process, are integrated in a regional modelling framework. Both frameworks are applied in a case study to 23 catchments located in the Thames river basin in the UK, which have a particularly wide range of geologies.

The thesis is concerned with the development, for the United Kingdom, of a systematic procedure for the synthesis of a design flood hydrograph. The emphasis is on the large scale application of the unit hydrograph/losses model and a review of changes in concept relating to this technique is presented. Nearly 1500 events from 138 United Kingdom catchments are studied; after data screening, runoff volume is expressed as a percentage of rainfall and the unit hydrograph is derived for each event. Certain innovations in techniques of hydrograph analysis are described. The unit hydrograph is simplified to a triangle the shape of which is controlled by a single parameter, the time to peak. This time to peak and the percentage runoff are regressed on catchment and event characteristics. It is recommended that time to peak should be predicted in terms of catchment characteristics only; the single most important variable is main channel slope. The main variables in the prediction of percentage runoff are indices of soil type and antecedent catchment condition.

No description available.

Current trends in sprinkler irrigation to improve application uniformity and reduce energy requirements haste led to problems of water application and potential surface runoff, which in turn have highlighted the importance of the soil and cultivation practice in making best use of irrigation water. The objective of this study was to begin the development of a mathematical model, which will simulate the operation of current sprinkler-soil-crop system, in order to provide a means of predicting surface runoff and so provide a more effective approach to system design. A model has now been developed which will predict runoff from a small simple agricultural catchment in the form of a ridge and furrow cultivation system. The model is based on the kinematic wave theory involving the continuity equation and the simplified momentum equation. A four-point implicit finite difference scheme is used to solve numerically the kinematic wave equations. The model (SROFF) may be used to predict the runoff at various times from a simple catchment with different slopes, water application rates and soil infiltration rate. A further development of the model was made by the introduction of the interception loss model (INCEPT) to predict the amount of water intercepted by the crop canopy during irrigation. The validity of the model was tested and supported by the results of laboratory experiments conducted on two soil samples with different infiltration rates, using three different application rates. The performance of the model was also evaluated by statistical test. There was good agreement between experiment and model results. The results indicated that this model can provide valuable information for the effective design of sprinkler systems, particularly where runoff may be a potential problem. This is particularly the case with current low pressure irrigation systems but equally the problem is common with high pressure systems when applied to soils with low infiltration rates.

The primary objective of this study is to investigate the runoff and quality variations exhibited on a medium-sized, agricultural catchment, dominated by a chalk and clay geology: the River Wallington, Hampshire, southern England. Emphasis has been focused on storm-based responses, particularly quality variations, monitored at two locations between October 1981 and May 1983. Quality parameters monitored include nitrate-nitrogen, phosphate, potassium, pH, chloride, sodium, suspended, volatile and dissolved solids, conductivity, temperature and dissolved oxygen. Stable rainfall and runoff conditions were observed with mean daily flows 0.2 m^3/s. Bankfall discharges of 10.0 m^3/s are exceeded at least once a year. Soil moisture status and antecedent catchment conditions are important factors in modelling observed runoff. Storm-based rainfall-runoff responses are adequately modelled using unit hydrograph techniques on seasonally divided data, with observed peak discharges estimated to within 10% and time to peak flows to within 2 hours. Definition of effective precipitation is a prime control on the performance of this prediction, particularly during the summer when more variable antecedent conditions occur. Loss of surface water as recharge to the Chalk aquifer complicates summer modelling. Rock and soil type are the major controls on surface water quality variations, which show stable responses during the study period. The influence of the Chalk maintains high pH, T.D.S., S.E.C. and NO_3-N concentrations, with long-term trends in the Chalk groundwater showing rising NO_3-N and Cl concentrations. Baseflow concentrations show minor dilution with higher discharges while stormflow concentrations show a wide range of behavioural responses with increasing flows, including dilution, concentration, flushing, between sample variability, and stable concentrations. The goodness-of-fit shown by bivariate concentration-discharge models used to describe the data are generally poor, indicating the importance of controls other than discharge in determining runoff quality. Mean storm concentrations show little change from the mean baseflow concentrations with orders of magnitude during storms typically: T.D.S. > V.S. > S.S. > Cl > Na > NO_3-N > D.O. > K > PO_4. The negligible concentration changes result in an increase in loads transferred during storms. The magnitude of increase depends on storm discharges but is typically double for solutes and fifty-fold for particulates. Storms are therefore important mechanisms of material transfer. (D72033/87)

This work has contributed to the understanding of dominant runoff generation at the large catchment scale and to the understanding of the relationships between landscape properties and hydrological behaviour. The developed models were used to estimate the climate change impact on the hydrology in the study catchment. A multivariate geochemical tracer survey was carried out in North Esk catchment in north east Scotland. A generic typology was developed using multivariate statistical methods to characterise the hydrochemical tracer response. Upland headwater runoff was dominant downstream in winter and provided significant flows during base flow periods in summer. These insights were complemented by a conjunctive analysis of long-term river flow data and a one year stable isotope survey. Integrative metrics of transit times, hydrometric responses, and catchment characteristics were explored for relationships at the large catchment scale. The evaluation that the associated soils and bedrocks, themselves controlling the flow path distribution, have a strong influence on the integrated hydrological catchment response. The empirically-based understanding of dominant runoff generation processes in the North Esk uplands and lowlands were used in a stepwise rainfall-runoff model development. Tracers were directly incorporated to reduce structural and parameter uncertainty. The integration of tracers helped reduce parameter uncertainty. These tracer-aided models increased confidence for using them to explore the effects of environmental change. Climate change impacts in the catchment where explored by forcing the models with projected climate change forcing from the UK Climate Projections 2009. The results revealed landscape-specific changes in the hydrological response with increased summer drought risk in the lowlands and diminishing snow influence and increased winter floods in the uplands. The spatial integration mediated the extremes observed in the subcatchments.

The effect of climate change and land use change on runoff generation and flooding has received great attention in many hydrological modelling studies. However, currently many hydrologists are still uncertain how much these two factors contribute to runoff generation, particularly in monsoon catchments. The river Kelantan is in one of the states in Malaysia, which experiences monsoon flooding, was used to investigate these two factors in effecting hydrologic response changes. Therefore, this study tries to provide a framework mainly to i) identify trends in the River Kelantan streamflow and explore the possible causes of that change, including precipitation change and land use changes; ii) disentangle and quantify the precipitation and land use and change effects on hydrological response and potential flooding in the River Kelantan catchment using past and current hydrological events; iii) simulate the future runoff scenarios (i.e. 2020s, 2050s and 2080s) using precipitation and land use changes projections. Historical data on the streamflow of the River Kelantan and precipitation in the Kelantan catchment were investigated for trends using the Mann-Kendall non-parametric method. In summary, a general pattern has been revealed in which streamflow is increasing in all seasons upstream, but is decreasing in the dry season downstream. The pattern in streamflow downstream is fairly well matched by increases in precipitation in the wet season and decreases in precipitation in the dry season. In the upstream area, the increases in streamflow are not matched by universal increases in precipitation, but rather by increases in the wet season only and decreases in the dry season, as for the downstream sub-catchment. The increases in streamflow in the dry season are, thus, more difficult to explain and land use change been performed and has been proven to cause a partial contribution of such observed trend in the upstream area. Subsequently, a study using the lumped HEC-HMS model to disentangle these two factors in causing hydrologic response changes (i.e. peak discharge and runoff volume) was performed. The results demonstrate that for the upstream area precipitation and land use changes led to the greatest increases in peak discharge and runoff volume. In contrast, in the downstream area the results suggest that precipitation trends may have led to significant increases in runoff generation. The simulation of hydrologic response in the future (i.e. 2020s, 2050s and 2080s) showed that climate change (i.e. precipitation change) has positive links with the peak discharge and runoff volume. If precipitation estimated to decrease using PRECIS A1B storyline from the SRES scenario, runoff was predicted to decrease and vice-versa. For the land use change impact, the scenario involved reducing the forested area, increasing the agricultural and built-up land caused runoff estimated to increase from 2020s to 2080s. The combined scenario demonstrated that precipitation change coupled with land use change has a significant impact to changes in peak discharge and runoff volume for the study area compared to climate change and land use change studies alone