摘要:

This study proposes a method for the estimation of lag time of forested mountainous watersheds. Hydrological flood-flow design methods require a time parameter, such as lag time or time of concentration, to estimate peak discharge and the flood hydrograph shape. Most existing methods used to compute the time parameter of a watershed are empirical and have been developed for urban or rural watersheds. Use of these methods for forested mountainous watersheds may result in severe underestimation of watershed response time and consequently, in overestimation of peak flood discharge. The water flow in a watershed is separated and analysed in two phases,viz.the land or hillslope phase and the stream channel phase. Most of the flow in a forested steep watershed is generated through subsurface pathways, and this knowledge, acquired from field experiments, is combined with kinematic wave equations to describe the generation of flow from steep forested hillslopes. This hillslope runoff is then used as input to the stream channels. Kinematic wave equations are developed for the runoff movement in the channels by assuming that both the roughness coefficient and the stream channel slope vary with the distance from the outlet of the watershed. These assumptions are validated and confirmed with data from the USA and Coastal British Columbia, Canada. The resulting equations are integrated to obtain an equation for the lag time. Comparison of the results of the proposed equation with data from two experimental watersheds in Coastal British Columbia and empirical equations used for the calculation of the lag time indicates that the proposed method is reliable and gives a good approximation of the observed lag time. These results are compared with other empirical equation, and it is shown that these earlier methods can result in severe underestimation of lag time.

ISSN:0262-6667    

DOI:10.1080/02626669609491475

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Wang (1991) reported that a genetic algorithm (GA), combined with a local search method, is an efficient and robust means for the calibration of conceptual rainfall-runoff models. In this article Wang's genetic algorithm has been slightly modified in order to improve its efficiency. The “optimal parameter set” produced by the GA has then been used as the starting point for a local optimization procedure based on Sequential Quadratic Programming (SQP). The purpose of this paper is to investigate the ability of the resulting algorithm, GA-SQP, to find the optimal parameter values during calibration of a conceptual rainfallrunoff (CRR) model. Two types of analysis were performed. The first refers to a theoretical case free of model and data errors, while the second refers to a real case in which the rainfall and runoff data were affected by evaluation errors. Specifically, in the synthetic data study, where the real set of parameters was knowna priori, a 100% success rate was observed, and in all cases the number of objective function evaluations remained relatively limited.

ISSN:0262-6667    

DOI:10.1080/02626669609491476

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The possibility of estimating groundwater inflow to irrigation drains in Minia, Egypt, using stable isotopes has been explored. The evaporation pan technique described here makes use of small variations in the concentration of naturally occurring stable isotopes (oxygen-18 and deuterium) in irrigation-fed groundwater and surface water as well as agricultural drainage water. The agreement between the stable isotope pan experiments carried out at Minia with others conducted at different locations in Egypt makes it feasible to estimate the inflow of groundwater to be about 42% of the total drainage water.

ISSN:0262-6667    

DOI:10.1080/02626669609491477

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The conceptual SACRAMENTO soil moisture accounting model and the physically based forest hydrological BROOK model have been used in runoff simulations for small and medium sized basins with the aim of investigating the contributions of different runoff components to the overall runoff. The simulations seem to confirm the results of previous experiments with environmental tracers in which prevailing contributions of groundwater have been reported.

ISSN:0262-6667    

DOI:10.1080/02626669609491478

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The concept of the dimensionless cumulant coefficient (YR), developed in the companion paper (Strupczewski & Dooge, 1995), is used to demonstrate that a linear interpolation between the two limiting cases of the Froude numberF0=0F0= 1 provides a good approximation to the higher cumulants of the channel response in the intermediate range of 0 < F0< 1. It is shown that the moments of any order R, either about the origin or about the centre follow the same linear interpolation rule as that applied to the impulse responses of the limiting cases. The first three cumulants are consequently the same in model and prototype. The fourth cumulants are made equal through the weighting factor of the linear interpolation. A study of the higher cumulants forR> 4 shows that the same basic linear interpolation holds forR= 5,R= 6, andR= 7 but not for values ofR⩾ 8. The analysis of the errors involved forR⩾ 5 shows that there is zero error forR= 5 and a small relative error in the middle of the range forR> 5. ForR= 5,R= 6 andR= 7, the error function is independent of the length of the channel as well as of the Froude number and the channel shape parameter(m).

ISSN:0262-6667    

DOI:10.1080/02626669609491479

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Approximate storage-reliability-resilience-yield (S-R-R-Y) relationships are derived for over-year water supply systems fed by autoregressive lag one Gamma and normal inflows. It is shown that a two-state Markov model may be exploited along with S-R-R-Y relationships to describe the general behaviour of over-year water supply systems. The two-state Markov model is also used to relate the probability of n-year no-failure operations (the concept of reliability used in the USA) to the steady-state probability of a system failure (the concept of reliability used in Australia and elsewhere) yielding a unified view of system reliability. Resiliency criteria are introduced which indicate whether or not a reservoir system is likely to return to normal operations once a failure has set in. These criteria indicate that the resilience of an over-year water supply system is generally independent of its steady-state reliability. The conditions under which finite reservoir systems behave like semi-infinite reservoir systems are also documented, and a factor is derived which describes the impact of the serial correlation of the inflows on the derived S-R-R-Y relationship.

ISSN:0262-6667    

DOI:10.1080/02626669609491480

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The stage-discharge relationship or rating curve at a river cross-section is a fondamental technique in hydrology employed for determining discharge from catchments. While river cross-sections are inherently variable, it generally takes quite some time for a change in cross-section to occur. Thus, where good quality data on stage and discharge are available, a stable and representative rating curve may be established. However, all too often, the natural variability is aggravated by data errors of human origin. These measurement errors occur because the routine of periodic flow measurement may be undertaken by illtrained personnel. Such errors resulting from this practice may lead to erroneous estimates of available water resources. This study discusses the derivation of a single rating curve for the Okavango River at Mohembo from measurements containing errors and outliers. It uses data transformation procedures, regression techniques and removal of outliers to derive a useful rating curve from suspect data. Finally, it Investigates the possibility of fitting a stochastic model to the discharge series. The results suggest that it may be possible to estimate missing data with an AR1MA model.

ISSN:0262-6667    

DOI:10.1080/02626669609491481

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The regional hydroclimatological effect of global climate change has been estimated and compared using a semi-empirical downscaling method with two versions (T21 and T42) of the general circulation model (GCM) developed at the Max Planck Institute for Meteorology, Germany. The comparisons were performed with daily mean temperature and daily precipitation amounts for the continental climate of the state of Nebraska, USA. Both the T21 and the T42 versions resulted in an increase of daily mean temperature under a 2 x C02 climatess. The magnitude of warming was substantially greater for T21 than for T42, except for February and June and at some stations in July where the T42 model suggested greater warming. Both GCMs resulted in a slight decrease in precipitation frequency and an increase in the amount of precipitation on wet days. Here, the T42 model again led to smaller changes. Different locations within Nebraska exhibited somewhat different temperature and precipitation responses with both GCM versions.

ISSN:0262-6667    

DOI:10.1080/02626669609491482

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669609491483

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669609491485

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor