摘要:

A subsidence research program began in 1985 to document the extent and magnitude of land subsidence in Sacramento Valley, California, an area of about 15 600 km2, using Global Positioning System (GPS) surveying. A brief description of GPS surveying is followed by a summary of each of four surveys between 1985 and 1989. In addition to periodic conventional spirit levelling, an examination was made of the changes in GPS-derived ellipsoidal height differences (summary differences) between pairs of adjacent bench marks in central Sacramento Valley from 1986 to 1989. The average rates of land subsidence in the southern Sacramento Valley for the past several decades were determined by comparing GPS-derived orthometric heights with historic published elevations. A maximum average rate of 0.053 m year−1(0.90 m in 17 years) of subsidence has been measured.

ISSN:0262-6667    

DOI:10.1080/02626669409492765

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An approach is presented for directly deriving a variable parameter Muskingum method from the St. Venant equations for routing floods in channels having any shape of prismatic cross-section and flow following either Manning's or Chezy's friction law. The approach also allows the simultaneous computation of the stage hydrograph corresponding to a given inflow or the routed hydrograph. This first paper also describes the solution procedure for routing the discharge hydrograph. A second paper (Perumal, 1994b) presents a verification of the methodology.

ISSN:0262-6667    

DOI:10.1080/02626669409492766

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The hydrodynamic derivation of a variable parameter Muskingum method and its solution procedure for estimating a routed hydrograph were presented in Part I of this series (Perumal, 1994a). In this paper, the limitations of the method, the criterion for its applicability and its accuracy are discussed based on the assumptions used. The method is verified by routing a given hypothetical inflow hydrograph through uniform rectangular cross-section channels and comparing the results with the corresponding numerical solutions of the St. Venant equations. The stage hydrographs as computed by the method are also compared with the corresponding St. Venant solutions. It is demonstrated that the method closely reproduces the St. Venant solutions for the discharge and stage hydrographs subject to the compliance of the assumptions of the method by the routing process.

ISSN:0262-6667    

DOI:10.1080/02626669409492767

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A laboratory experiment was designed to determine the spectral characteristics of different types of sediment suspended in water in the visible and near infrared wavelengths (0.45–0.9 μm) using a four-channel radiometer. Field collected sediments were resuspended in water to produce different concentration levels for the measurement of radiance. Spectral measurements of turbid water showed a distinctive difference in the behaviour of radiance with change in the inorganic suspended sediment concentration and type. It was noted that the correlation between the suspended sediment concentration and the radiance varied with the mineral composition of the sediment. The clay minerals of low specific gravity had larger values of radiance than those from high specific gravity nonclay minerals. Based on the results obtained, it appears that an algorithm to estimate suspended sediment concentration can be developed from radiance.

ISSN:0262-6667    

DOI:10.1080/02626669409492768

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Forest harvesting practices have been shown to have a hydrological impact that is akin to bushfire regeneration. Fine resolution fossil pollen studies in the upper Delegate River basin, East Gippsland, Australia, have revealed large changes in the reproductive activity of aquatic plants synchronous with the onset of harvesting activities. This paper seeks to establish an explanation for these changes by applying a 2-parameter regional bushfire yield trend model to the wet eucalypt forests above the pollen core site. Using histories of piecemeal coupe (harvesting plot) development, the model was used to reconstruct annual runoff yields between 1970 and 1991 assuming zero harvesting. The results indicated a progressive reduction in simulated annual yields (relative to the zero disturbance scenario) attaining between 20 and 55% loss by 1987/1988. Given the historic rate of harvesting, over a 50% reduction of water yield is expected to occur by 2005 due to factors including enhanced forest transpiration. Such hydrological changes would have significant implications for downstream fauna and flora and for stream dynamics.

ISSN:0262-6667    

DOI:10.1080/02626669409492769

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In order to support the effort of Environment Canada directed to the automation of surface water quantity data management, an Intelligent Decision Support System (IDSS), to be used to create, develop and maintain stage-discharge (S-D) rating curves, is in the final stage of development. Environment Canada is the agency responsible for establishing gauging stations and monitoring streamflow in Canada. Hydraulic data such as stage and discharge are measured at these stations and used for the development of S-D rating curves. These in turn are cross-referenced with continuous water level recordings to generate daily stream discharges. The current procedure for establishing S-D curves used by Environment Canada is subjective, due to the manual labour involved in the plotting of measurements, analysing of data points and decision making to alter or update an existing curve. The IDSS computer system is based on the concept of representing rating curves with mathematical models or equations. The paper describes the main characteristics of the modelling module of the IDSS. Linear regression is the modelling technique used within the IDSS together with power and Box-Cox transformations introduced to achieve linearity of the data. Within the module presented in the paper, the generation of multiple S-D curves is combined with comprehensive statistical and multi-objective analyses in order to select an optimal mathematical model or equation.

ISSN:0262-6667    

DOI:10.1080/02626669409492770

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The dominant source of streamflow in many mountainous watersheds is snowmelt recharge through shallow groundwater systems. The hydrological response of these watersheds is controlled by basin structure and spatially distributed snowmelt. The purpose of this series of two papers is to simulate spatially varying snowmelt and groundwater response in a small mountainous watershed. This paper examines the spatially and temporally variable snowmelt to be used as input to the groundwater flow modelling described in the second paper. Snowmelt simulation by the Simultaneous Heat and Water (SHAW) model (a detailed process model of the interrelated heat, water and solute movement through vegetative cover, snow, residue and soil) was validated by applying the model to two years of data at three sites ranging from shallow transient snow cover on a west-facing slope to a deep snow drift on a north-facing slope. The simulated energy balances for several melt periods are presented. Snow depth, density, and the magnitude and timing of snow cover outflow were simulated well for all sites.

ISSN:0262-6667    

DOI:10.1080/02626669409492771

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The impacts of spatial and temporal variations of snowmelt recharge on subsurface flow in a small mountainous watershed were investigated using field measurements and numerical simulations. A two-dimensional, variably saturated flow model (VAM2D) was used to characterize the hillslope aquifer and to delineate subsurface flow mechanisms. Spatially varying snowmelt along a hillslope transect described in the preceding paper were used as input for the subsurface flow analyses. Simulations indicated that the heterogeneous hillslope aquifer provides hydrogeological conditions for confined and unconfined groundwater flow depending on the extent of snowmelt recharge. The spatial and temporal distribution and amount of snowmelt recharge play important roles in determining when flow is governed by confined and unconfined flow. Results showed that the VAM2D model was able to simulate piezometric measurements reasonably using calibrated hydraulic parameters. Sensitivity analyses showed that the flow regime was considerably different when the spatial variation of snowmelt was not considered.

ISSN:0262-6667    

DOI:10.1080/02626669409492772

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Estimation of soil loss from single storm events is essential for basin planning and nonpoint source pollution control. Rainfall-runoff erosivity factors for single storm events in northern Iraq were derived from the basic theory of soil detachment and transport. The factors derived are a single parameter which includes runoff depth only and a factor which combines runoff depth and peak rate. These two erosivity factors gave satisfactory results when tested using data from natural runoff plots collected at different sites in the region. The same data were then used to test the applicability of various established erosivity factors. The two derived erosivity factors were superior to any known erosivity factor tested in the region. These include factors currently in use in Universal Soil Loss Equation (USLE) applications in different parts of the world.

ISSN:0262-6667    

DOI:10.1080/02626669409492773

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669409492774

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor