Rainfall trends in arid and semi-arid regions of Iran

Spatial and temporal variability of annual precipitation during 1961-2006 in Yellow River Basin, China

Hydraulic geometry is of fundamental importance in planning, design, and management of river engineering and training works. Although some concepts of hydraulic geometry were proposed toward the end of the nineteenth century, the real impetus toward formulating a theory of hydraulic geometry was provided by the work of Leopold and Maddock (1953). A number of theories have since been proposed.Some of the theories are interrelated but others are based on quite different principles. All theories,however, assume that the river flow is steady and uniform and the river tends to attain a state of equilibrium or quasi-equilibrium. The differences are due to the differences in hydraulic mechanisms that the theories employ to explain the attainment of equilibrium by the river.

On the theories of hydraulic geometry

This study extends the earlier contribution of Julien and Wargadalam in 1995. A larger database for the downstream hydraulic geometry of alluvial channels is examined through a nonlinear regression analysis. The database consists of a total of 1,485 measurements, 1,125 of which describe field data used for model calibration. The remaining 360 field and laboratory measurements are used for validation. The data used for validation include sand-bed, gravel-bed, and cobble-bed streams with meandering to braided planform geometry. The five parameters describing downstream hydraulic geometry are: channel width W, average flow depth h, mean flow velocity V, Shields parameter τ* , and channel slope S. The three independent variables are discharge Q, median bed particle diameter ds, and either channel slope S or Shields parameter τ* for dominant discharge conditions. The regression equations were tested for channel width ranging from 0.2 to 1,100 m , flow depth from 0.01 to 16 m , flow velocity from 0.02 to 7 m∕s ...

https://www.engr.colostate.edu/%7Epierre/ce_old/Projects/Paperspdf/Lee-Julien-ASCE-06.pdf

Downstream Hydraulic Geometry of Alluvial Channels

The temporal trends of reference evapotranspiration (ETref) reflect the combined effects of radiometric and aerodynamic variables, such as global solar radiation (Rs), wind speed, relative humidity and air temperature The temporal trends of annual ETref during 1961–2006 calculated by Penman-Monteith method were explored and the underlying causes for these trends were analysed in the Yellow River Basin (YRB) The contributions of key meteorological variables to the temporal trend of ETref were detected using the detrended method and then sensitivity coefficients of ETref to meteorological variables were determined For ETref, positive trends in the upper, middle and whole of YRB, and significant negative trend (P = 0·05) in the lower basin were obtained by the linear fitted model Significant increasing trend (P = 0·05) in air temperature and decreasing trend in relative humidity were the main causes for the increasing trends of ETref in the upper, middle and whole basins For the whole basin, the increasing trend of ETref was mainly caused by the significant increase (P = 0·05) in air temperature and to a lesser extent by a decrease in the relative humidity, decreasing trends of Rs and wind speed reduced ETref The spatial distribution of sensitivity coefficients addressed that the sensitive regions for ETref response to the changes of the four meteorological variables are different in the YRB The sensitive region lay in the upper basin for Rs, the northwest portion of the middle basin for wind speed, the south portion of YRB for relative humidity and the west portion of the upper basin and the north portion of the middle basin for air temperature In general, Rs was the most sensitive variable for ETref, followed by relative humidity, air temperature and wind speed in the basin scale Copyright © 2010 John Wiley & Sons, Ltd

The temporal trends of reference evapotranspiration and its sensitivity to key meteorological variables in the Yellow River Basin, China

This paper presents a time-series methodology by which a significant trend in climatological variables can be identified and notes how this trend may be related to other climatological variables. The evapotranspiration (ET) record at a monitoring site near Davis, California, shows an upward trend in both the ET and wind speed series. A review of the site history indicates that the upward trend in the wind series is due to relocating the site from the middle of an agricultural field to a more open area. Further analysis of the series indicates that this increase in wind speed has some effect on the yearly ET totals, but could not be used to completely explain the increasing trend in ET.

Method for Trend Detection in Climatological Variables

Alluvial channels, in the context of this paper, are unlined man-made channels with predetermined bed slopes used to convey water that carries sediment. An extremal hypothesis is presented, namely, an alluvial channel attains a stable width when the rate of change of unit stream power with respect to its width is a minimum. An easy-to-use width control parameter is presented and compared with a form of Lacey's silt factor. The hypothesis is tested on data from canals located in the Punjab and Sind provinces of Pakistan.

Stable Width of an Alluvial Channel

A computer model for the simulation of canal operation was developed. The model is applicable for any nonbranching canal system composed of a series of channels separated by control structures. The programming language used was BASIC, a language suitable to most microcomputers. The Delta Field Division Canal of the California Aqueduct was used for an example simulation and verification. A comparison of data computed by the model to observed data indicated good agreement.

Johannes J. DeVries

Papers

Method for Trend Detection in Climatological Variables

Stable Width of an Alluvial Channel

Microcomputer simulation of canal operation