摘要:

Runoff and soil erosion are known to cause a degradation in soil and water quality. Six natural runoff plots (three 10 m long and three 30 m long) were established on 6% uniform slope area for the study of P and N losses associated with runoff and soil erosion in northern Iraq. The soil at the site belongs to the Calciorthid suborder which dominates in the low rainfall zone of northern Iraq. Runoff, erosion, and associated P and N losses, were recorded from these plots for three rainfall seasons. Results illustrated that eroded sediment is always rich in available P and inorganic N compared to the original soil. Concentrations of soluble P and soluble N in runoff illustrated significant variability both between storms and between seasons. Both sediment-bound P and soluble P were significantly correlated with the ratio of runoff to rainfall.

ISSN:0262-6667    

DOI:10.1080/02626669909492265

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Monthly rainfall amounts are distributed according to different frequency distribution functions in different parts of the world. However, in extremely arid regions gamma probability distribution functions are most often found to fit the existing data well. Libyan monthly rainfall distributions are found to abide by gamma probability distribution function which is confirmed on the basis of chi-square tests. Almost all the rainfall sequences recorded for at least the last 20 years in Libya are investigated statistically and gamma distribution parameters are calculated at existing stations. The shape and scale parameters are then regionalized and hence it becomes possible to find the parameter values at any desired location within the study area and then to generate synthetic sequences according to the gamma distribution. Predictions of 10, 25, 50 and 100 mm rainfall amounts are achieved by this probability function.

ISSN:0262-6667    

DOI:10.1080/02626669909492266

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Kanchanapally watershed covering an area of about 11 km2in Nalgonda district, Andhra Pradesh, India is located in granitic terrain. Groundwater recharge has been estimated from a water balance model using hydrometeorological data from 1978–1994. The monthly recharge estimates obtained from the water balance model formed input for the groundwater flow model during transient model testing. The groundwater flow model has been prepared to simulate steady state groundwater conditions of 1977 using the nested squares finite difference method. The transient groundwater flow model has been tested during 1977–1994 using the estimated recharge values. The present study helped verify the usefulness of monthly recharge estimates for accounting dynamic variations in recharge as reflected in water level fluctuations in hydrographs.

ISSN:0262-6667    

DOI:10.1080/02626669909492267

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

With the operation and maintenance of streamgauging networks in many developing countries coming under increasing pressure through lack of funds and suitably trained personnel, greater reliance must be placed on procedures for transferring information from gauged to ungauged catchment areas. These approaches to generalizing hydrological variables, such as the quantiles of the frequency distributions of floods and low flows, are collectively referred to as regionalization methods. An important feature of these methods is the demarcation of hydrologically homogeneous regions. The latter may be regarded as an example of the wider problem of classification of data sets, for which a variety of modern informatic tools, such as artificial neural networks and fuzzy sets, may be invoked. Application of examples of these techniques to flood data for the southwest of England and Wales has demonstrated that classes may be defined by Representative Regional Catchments (RRCs), whose characteristics are hydrologically more appealing than those imparted merely by geographical proximity. The techniques employed, Kohonen networks and fuzzy c-means, are straightforward in application, and were found to identify broadly similar RRCs. The results indicate the feasibility of employing these methodologies on a country-wide basis.

ISSN:0262-6667    

DOI:10.1080/02626669909492268

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A river flow regime describes an average seasonal behaviour of river flow, usually representing a set of long-term monthly mean values. Seasonal patterns of flow can be regular, repeating in principle the same pattern from year to year, or irregular, i.e. alternating between a couple of different regime types during individual years. By tradition, a river flow regime has been considered as a static characteristic that does not change in large temporal scale, yet this may be an oversimplification with regard to constantly changing environmental conditions. Such a “static” description of a flow regime, based on long-term mean values is in discrepancy with the dynamic character of the system described. The dimension of this system in terms of fractal and intrinsic dimensions has been investigated on an example of Scandinavian runoff series by different methods: from a simple graphic method to determine the fractal dimension to empirical orthogonal function (EOF) and entropy-based aggregation to outline the number of patterns necessary for representing the regimes of different intrinsic dimension of a set of point data. The series studied demonstrated a variety of fractal and intrinsic dimensions that were well in agreement with the stability character of the investigated regime types. The less stable the regime, the higher were its fractal and intrinsic dimensions and the number of variables required for its description.

ISSN:0262-6667    

DOI:10.1080/02626669909492269

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The sediment delivery processes due to the travel along a hydraulic path having an uniform slope and to the concave shape of the path are modelled. In particular, using a power equation for modelling the slope profile and RUSLE with two different expressions of the topographic factors, a criterion to define the erosion active slope length, i.e. the slope length in which no deposition processes occur, is initially proposed. Then, the RUSLE equation is adapted to concave profiles by a correction factor of the topographic factors depending on slope curvature. Finally, the deduced relationships (equations (19) and (27)) for correcting the topographic factors for a concave slope are experimentally tested, comparing the calculated sediment yield values with the measurements carried out at the outlets of three small Calabrian basins.

ISSN:0262-6667    

DOI:10.1080/02626669909492270

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Estimates of groundwater recharge are often needed for a variety of groundwater resource evaluation purposes. A method for estimating long-term groundwater recharge and actual evapotranspiration not known in the English literature is presented. The method uses long-term average annual precipitation, runoff, potential evaporation, and crop-yield information, and uses empirical parameter curves that depend on soil and crop types to determine long-term average annual groundwater recharge (GWR). The method is tested using historic lysimeter records from 10 lysimeters at Coshocton, Ohio, USA. Considering the coarse information required, the method provides good estimates of groundwater recharge and actual evapotranspiration, and is sensitive to a range of cropping and land-use conditions. Problems with practical application of the technique are mentioned, including the need for further testing using given parameter curves, and for incorporating parameters that describe current farming practices and other land uses. The method can be used for urban conditions, and can be incorporated into a GIS framework for rapid, large-area, spatially-distributed estimations ofGWR. An example application of the method is given.

ISSN:0262-6667    

DOI:10.1080/02626669909492271

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper assesses one of many potential enhancements to conventional flood forecasting that can be achieved through the use of soft computing technologies. A methodology is outlined in which the forecasting data set is split into subsets before training with a series of neural networks. These networks are then recombined via a rule-based fuzzy logic model that has been optimized using a genetic algorithm. The methodology is demonstrated using historical time series data from the Ouse River catchment in northern England. The model forecasts are assessed on global performance statistics and on a more specific flood-related evaluation measure, and they are compared to benchmarks from a statistical model and naive predictions. The overall results indicate that this methodology may provide a well performing, low-cost solution, which may be readily integrated into existing operational flood forecasting and warning systems.

ISSN:0262-6667    

DOI:10.1080/02626669909492272

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The uncertainties arising from the problem of identifying a representative model structure and model parameters in a conceptual rainfall-runoff model were investigated. A conceptual model, the HBV model, was applied to the mountainous Brugga basin (39.9 km”) in the Black Forest, southwestern Germany. In a first step, a Monte Carlo procedure with randomly generated parameter sets was used for calibration. For a ten-year calibration period, different parameter sets resulted in an equally good correspondence between observed and simulated runoff. A few parameters were well defined (i.e. best parameter values were within small ranges), but for most parameters good simulations were found with values varying over wide ranges. In a second step, model variants with different numbers of elevation and landuse zones and various runoff generation conceptualizations were tested. In some cases, representation of more spatial variability gave better simulations in terms of discharge. However, good results could be obtained with different and even unrealistic concepts. The computation of design floods and low flow predictions illustrated that the parameter uncertainty and the uncertainty of identifying a unique best model variant have implications for model predictions. The flow predictions varied considerably. The peak discharge of a flood with a probability of 0.01 year−1, for instance, varied from 40 to almost 60 mm day−1. It was concluded that model predictions, particularly in applied studies, should be given as ranges rather than as single values.

ISSN:0262-6667    

DOI:10.1080/02626669909492273

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Water quality changes taking place during the infiltration process of treated wastewater produced by the Yeast Industrial Company, Jordan, are discussed. It was found that the COD, NH4+and PO43-contents decreased with depth. More than 80% of NH4+and about 95% of PO43and COD were removed at a depth of 70 cm in the soil profile. However, the electrical conductivity (EC) of the infiltrated water, which was extracted from different depths, increased gradually due to the dissolutional processes of soluble minerals within the soil profile. Furthermore, the probable effect of the irrigation return flows of the treated wastewater used in irrigation on the groundwater resources of the area are discussed. Generally, it was found that land application of this sort of wastewater is an efficient method of further treatment taking into consideration the negligible effects of the wastewater on the groundwater resources in the area.

ISSN:0262-6667    

DOI:10.1080/02626669909492274

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor