摘要:

The use of dimensionless cumulants to characterize the shape of the linear response of a semi-infinite prismatic channel is extended and simplified by means of the dimensionless coefficient (γR) linking the Rth order shape factor to the 3rd order shape factor raised to the power of (R—2). It is shown that, for the special structure of the cumulants of the linearized St. Venant equations, the dimensionless cumulant coefficient (γR) of any order R > 4 is a single-valued function of γ4. It is also shown that the value of γRfor any Froude number F0combined with any shape of section and any friction law (both characterized by the parameter m) is intermediate between the values for the two limiting cases of the diffusion analogy model (F0= 0) and the rapid flow model (F0= 1). The dimensionless cumulant coefficient γRis related to γ4through a parameter p(m, F0) by a polynomial of order [R/2]—1.

ISSN:0262-6667    

DOI:10.1080/02626669509491458

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Evapotranspiration (ET) is an important process in the hydrological cycle and needs to be accurately quantified for proper irrigation scheduling and optimal water resources systems operation. The time variant characteristics of ET necessitate the need for forecasting ET. In this paper, two techniques, namely a seasonal ARIMA model and Winter's exponential smoothing model, have been investigated for their applicability for forecasting weekly reference crop ET. A seasonal ARIMA model with one autoregressive and one moving average process and with a seasonality of 52 weeks was found to be an appropriate stochastic model. The ARIMA and Winter's models were compared with a simple ET model to assess their performance in forecasting. The forecast errors produced by these models were very small and the models would be promisingly of great use in real-time irrigation management.

ISSN:0262-6667    

DOI:10.1080/02626669509491459

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Since eroded sediments are produced from different sources distributed throughout a basin, sediment delivery processes at basin scale have to be modelled by a spatially distributed approach. In this paper a new theoretically based relationship is proposed for evaluating the sediment delivery ratio, SDRi, of each morphological unit, i, into which a basin is divided. Then, using the sediment balance equation written for the basin outlet, a relationship between the basin sediment delivery ratio, SDRWand the SDRiis deduced. This relationship is shown to be independent of the soil erosion model used. Finally, a morphological criterion for estimating a coefficient, β, is proposed.

ISSN:0262-6667    

DOI:10.1080/02626669509491460

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An approach for better understanding of the physical implication of estimated aquifer parameters is demonstrated by analysing the pumping test data at Cottam in the Nottingham aquifer, UK. A sensitivity analysis showed that the area represented by the estimated parameters was much smaller than the area covered by the depression cone. After parameters are estimated, further research should be carried out to understand what portions of the aquifer the parameters represent. The parameters estimated at Cottam represented mainly aquifer features between roughly 100 and 2000 m. The sensitivity analysis also showed that the observed drawdown being satisfactorily matched by a model with uniform parameters does not prove that the aquifer is homogeneous. Slightly anomalous data may imply the existence of large anomalous zones. Although the drawdowns at Cottam could be ‘satisfactorily’ fitted by a model with uniform parameters, the fit could be improved by a model using a more permeable aquifer but with a zone about 700 m wide and with 42% less transmissivity.

ISSN:0262-6667    

DOI:10.1080/02626669509491461

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper presents an expert system to help select the best method to estimate design flood flows for civil engineering works based upon the procedures available, the nature and characteristics of the basin and existing hydrological records. The system presents the user with a list of possible methods ranked in descending grade order and optionally presents explanations which support the selected choices. Ordering is achieved using the knowledge base provided by the expert. The system recommends procedures for both preliminary estimates and final designs. The system also constitutes a valuable aid for junior engineers and experienced hydrologists in the selection of methods. Its conceptual structure can be easily generalized to treat other problems of a similar nature in the field of hydrology and water resources.

ISSN:0262-6667    

DOI:10.1080/02626669509491462

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Problems associated with the application of monthly rainfall-runoff models to arid and semiarid areas for water resource estimation purposes are discussed with respect to the representation of hydrological processes and the model rainfall input. The problems are illustrated using a specific monthly model applied to catchments within the semiarid to arid parts of southern Africa. Some model improvements are suggested and briefly evaluated and the application of a daily model to one of the catchments is compared. The overall conclusion is that while a detailed examination of the available rainfall data can account for many of the inadequate simulation results on an individual month basis, it is difficult to make allowances for the lack of resolution in the normally available information. Other problems related to the structure of individual models can be surmounted by limited model developments, but very little can be done to bypass the rainfall quantification problem.

ISSN:0262-6667    

DOI:10.1080/02626669509491463

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Using a combination of laboratory and field experiments, the performance of a Partech Instruments Ltd IR40-C active head suspended solids sensor has been tested with respect to changing particle size distribution and rapid variation in suspended sediment transport rate. The sensor, which utilizes light attenuation in the infrared waveband, has several advantages both over visible light optical designs and over nuclear or optical back-scatter (OBS) devices. Three sets of laboratory tests are reported: calibration experiments using estuarine, pro-glacial and control media; flume simulations of pulsed sediment supply at a variety of frequencies, concentrations and ambient flow velocities; and simple tests for the effect of air bubbles within the sensor light path. The sensor was also deployed in the field, together with an electromagnetic current meter, to monitor flow and suspended sediment transport fluctuations in the turbulent frequency range. Although the sensor performed well with respect to drift, noise and stability of calibration, significant variation occurred with respect to suspensions of differing particle sizes. A simple correction procedure involving the weighting of sensor output by specific particle surface area may enable comparison of turbidity data from different locations and times, and with standard calibration solutions. At high frequencies, the sensor is capable of resolving fluctuations in the transport rate to c. 0.5 s, which appears to correspond well to field observations of significant velocity fluctuation and transport ‘events’ and is comparable with results obtained using OBS devices. However, the resolution of transport fluctuations is again dependent upon particle characteristics, and the presence of air bubbles in the flow whose size approximates the path width of the sensor may mimic a fluctuating transport process. Further interpretation of high frequency measurement awaits research into the fundamentals of rapidly varying flow and sediment transport characteristics.

ISSN:0262-6667    

DOI:10.1080/02626669509491464

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491465

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491466

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491467

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor