摘要:

Supraglacial Imja Lake (lake level, 5010 m a.m.s.l.), Khumbu, Nepal Himalaya, has increased its size on the tongue of Imja Glacier since the 1950s. In order to clarify the mechanism of the lake expansion, the physical conditions, water budget and heat budget of the lake were examined by measuring water temperature, water turbidity, lake level, meteorology and water discharge. These measurements were carried out in the monsoon season of July 1997, when the glacier melt occurred in the ablation area with air temperature of more than 0°C. Density stratification in the lake is built up by an effect of water pressure on lake water, but, neglecting the effect, lake water density is defined by suspended sediment concentration rather than temperature. Glacier-melt water from the subaqueous part of the glacier terminus mixed with lake surface water of 4–8°C, and diffused the water of about 3°C into the deeper zone of the lake. This advective, thermal diffusion occurs by sediment-laden underflow and relatively clear density interflow. The sediment-laden underflow is induced by intermittent glacier-melt sediment discharge at the terminus, while the density interflow is probably produced by continuous glacier-melt water discharge. Calculation of water budget of the lake indicates that meltwater inflow at the glacier terminus and surface water outflow at the outlet determine the hydrological conditions of the lake. The net heat transfer by melting of the terminal ice and dead ice, connected to the lake expansion, was evaluated by calculating the heat budget of the lake.

ISSN:0262-6667    

DOI:10.1080/02626660009492353

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper presents four different approaches for integrating conventional and AI-based forecasting models to provide a hybridized solution to the continuous river level and flood prediction problem. Individual forecasting models were developed on a stand alone basis using historical time series data from the River Ouse in northern England. These include a hybrid neural network, a simple rule-based fuzzy logic model, an ARMA model and naive predictions (which use the current value as the forecast). The individual models were then integrated via four different approaches: calculation of an average, a Bayesian approach, and two fuzzy logic models, the first based purely on current and past river flow conditions and the second, a fuzzification of the crisp Bayesian method. Model performance was assessed using global statistics and a more specific flood related evaluation measure. The addition of fuzzy logic to the crisp Bayesian model yielded overall results that were superior to the other individual and integrated approaches.

ISSN:0262-6667    

DOI:10.1080/02626660009492354

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Flood forecasting is of prime importance when it comes to reducing the possible number of lives lost to storm-induced floods. Because rainfall-runoff models are far from being perfect, hydrologists need to continuously update outputs from the rainfall-runoff model they use, in order to adapt to the actual emergency situation. This paper introduces a new updating procedure that can be combined with conceptual rainfall-runoff models for flood forecasting purposes. Conceptual models are highly nonlinear and cannot easily accommodate theoretically optimal methods such as Kalman filtering. Most methods developed so far mainly update the states of the system, i.e. the contents of the reservoirs involved in the rainfall-runoff model. The new parameter updating method proves to be superior to a standard error correction method on four watersheds whose floods can cause damage to the greater Paris area. Moreover, further developments of the approach are possible, especially along the idea of combining parameter updating with assimilation of additional data such as soil moisture data from field measurements and/or from remote sensing.

ISSN:0262-6667    

DOI:10.1080/02626660009492355

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Detection of nonstationarity in series of flow records is of vast scientific and practical significance. In order to develop guidance as to the choice of an appropriate test, among the many candidates, one has recourse to analysis of a controlled trend artificially introduced to generated data mimicking river flow observations. Raw series of good quality flow data were normalized and de-seasonalized and subsequently transformed to the Fourier spectral domain. Keeping the power spectrum preserved, the phase spectrum was subjected to randomization. After transformation back to the temporal domain, the data were contaminated with trends and step changes in a controlled way. The results evaluate the detectability of nonstationarity by particular tests as a quasi-continuous function of magnitude of the contaminating change. A method is devised to compare the tests' performance, with the objective of choosing an appropriate tool. Analysis of detectability versus change magnitude gives a new insight, of direct practical applicability, into the properties of the tests. Further insight is provided by examining over 200 real series of river flow records.

ISSN:0262-6667    

DOI:10.1080/02626660009492356

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

To investigate the consequences of climate change on the water budget in small catchments, it is necessary to know the change of local precipitation and temperature. General Circulation Models (GCM) cannot provide regional climate parameters yet, because of their coarse resolution and imprecise modelling of precipitation. Therefore downscaling of precipitation and temperature has to be carried out from the GCM grids to a small scale of a few square kilometres. Daily rainfall and temperature are modelled as processes conditioned on atmospheric circulation. Rainfall is linked to the circulation patterns (CPs) using conditional probabilities and conditional rainfall amount distribution. Both temperature and precipitation are downscaled to several locations simultaneously taking into account the CP dependent spatial correlation. Temperature is modelled using a simple autoregressive approach, conditioned on atmospheric circulation and local areal precipitation. The model uses the classification scheme of the German Weather Service and a fuzzy rule-based classification. It was applied in the Aller catchment for validation using observed rainfall and temperature, and observed classified geopotential pressure heights. GCM scenarios of the ECHAM model were used to make climate change predictions (using classified GCM geopotential heights); simulated values agree fairly well with historical data. Results for different GCM scenarios are shown.

ISSN:0262-6667    

DOI:10.1080/02626660009492357

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The River Kali in western Uttar Pradesh, India is a typical water course for untreated municipal and industrial effluents. The river receives considerable amounts of waste every day from the industries and municipal area of Muzaffarnagar town. Agricultural runoff is the other major factor in pollution of the river water. The mass balance calculations conducted on the river reach indicate that nitrate and phosphate from the non-point sources constitute 32.4 and 11.2% of the total load, respectively. The resulting differential loading, if adjusted for uncharacterized non-point contribution to the load, may represent the total point sources load to the river minus any losses due to volatilization, settling, and/or degradation. Indirect monitoring using upstream/downstream sampling locations provides a viable alternative to conventional methods for measuring the changes in the concentration and/or load to the river.

ISSN:0262-6667    

DOI:10.1080/02626660009492358

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Well storage effect is generally considered while interpreting pumping test data from large diameter wells. However, in an aquifer of low permeability, the well storage is found to be significant during pumping tests conducted on bore wells. The interpretation of such data gives ambiguous results unless well storage effect is taken into account. A field example is presented to illustrate the difficulty in interpretation of the pumping test data. In order to take into account the well storage effect, a finite difference approach of interpreting pumping test data is suggested.

ISSN:0262-6667    

DOI:10.1080/02626660009492359

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A simplified method has been developed for solving leaky aquifer non-Darcian flow hydraulics. The principle of volumetric approach is combined with the confined-aquifer, time-dependent drawdown equation in an observation well. The groundwater flow in the leaky aquifer is assumed to obey a non-Darcian flow law of exponential type. The results are obtained in the form of type-curve expressions from which the necessary bundles of curves are drawn for a set of selective non-Darcian flow aquifer parameters. Although application of the methodology appears as rather limited but it provides a scientific contribution and extension of leaky aquifer theory towards nonlinear flow conditions. The methodology developed herein is applied to some actual field data from the eastern sedimentary basin in the Kingdom of Saudi Arabia.

ISSN:0262-6667    

DOI:10.1080/02626660009492360

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Colorado River is one of the most highly regulated and extensively utilized rivers in the world. Total reservoir storage is approximately four times the mean annual runoff of −17 × 109m3year−1. Reservoir storage and regulation have decreased annual peak discharges and hydroelectric power generation has increased daily flow variability. In recent years, the incidental impacts of this development have become apparent especially along the Colorado River through Grand Canyon National Park downstream from Glen Canyon Dam and caused widespread concern. Since the completion of Glen Canyon Dam, the number and size of sand bars, which are used by recreational river runners and form the habitat for native fishes, have decreased substantially. Following an extensive hydrological and geomorphic investigation, an experimental flood release from the Glen Canyon Dam was proposed to determine whether sand bars would be rebuilt by a relatively brief period of flow substantially greater than the normal operating regime. This proposed release, however, was constrained by the Law of the River, the body of law developed over 70 years to control and distribute Colorado River water, the needs of hydropower users and those dependent upon hydropower revenues, and the physical constraints of the dam itself. A compromise was reached following often difficult negotiations and an experimental flood to rebuild sand bars was released in 1996. This flood, and the process by which it came about, gives hope to resolving the difficult and pervasive problem of allocation of water resources among competing interests.

ISSN:0262-6667    

DOI:10.1080/02626660009492361

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626660009492362

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor