Search

Doubts have been expressed about the validity of the critical depth defined in terms of the minimum specific energy head of the free-surface streamline when dealing with developing open-channel flows. This note examines the two approaches for defining critical flow, that based on the minimum specific energy of the free-surface streamline and that based on the mean energy head of the whole flow section. Large differences for the dimensionless critical depths are obtained with the two methods due to each critical depth proving to be a different control point on the free-surface profile. It is argued that both methods are different alternatives, although the critical depth concept was different in each case. Theoretical support to critical flow computations based on the free streamline is provided. An alternative approach for computing the discharge characteristics of broad-crested weirs based on the energy loss inside the boundary layer is also proposed. DOI: 10.1061/(ASCE)HY.1943-7900.0000142 CE Database subject headings: Open channel flow; Boundary layers; Critical flow; Weirs. Author keywords: Open channels; Boundary layers; Critical flow; Weirs.

The critical flow principle is a useful approach for the hydraulic analysis of round-crested weirs due to their single head-discharge relationships. The hydraulics of circular-crested weirs is examined using simplified models incorporating streamline curvature effects, comparing their predictions with experimental data. A generalized one-dimensional model based on the critical flow in curvilinear motion has been developed. The discharge coefficient increases with the specific energy normalized with the radius of curvature, E/R, when streamline curvature effects are included. The relative flow depth at the crest decreases as E/R increases. The flow at the weir crest is only critical for a normalized specific energy value of E/R [approximately equal to] 0.5-0.6. For larger heads, the flow at the weir crest has been found to be supercritical. CE Database subject headings: Open channels; Critical flow; Weirs.

The singular point is a physical phenomenon consistent with critical flow conditions, and, consequently, the real control section of a water surface profile. A general method to study the location, type, and water surface slope of a singular point is described. This method, in addition to improving the classic gradually-varied flow theory, can be used for the design of channel contractions involving transcritical flows, as in the case of chute spillways and inlets to river diversion tunnels. The method is explained in the case of a chute spillway and verified against experimental data recorded in a Venturi channel. DOI: 10.1061/(ASCE)0733-9429(2008)134:4(492) CE Database subject headings: Open channels; Gradually-varied flow; Spillways; Transcritical flow.

A numerical study to describe the transition regime between the skimming and wake interference flows due to the influence of an idealized bed roughness in a water flume was carried out here using the lattice model approach. The model reproduced the skimming, transition, and wake interference regimes for different aspect ratios that determine the bed roughness geometry. The simulated turbulent structures were visualized by drawing the trajectories of a large number of passive tracer particles released in the computational domain, and the results agreed with those reported by the research works. The dimensionless streamwise and vertical turbulent intensities were calculated at five test sections. The results obtained supported the visualized flow patterns permitting us to detect the presence of a shear layer developed at the top of the roughness element, whose strength varied according to the flow regime simulated. DOI: 10.1061/(ASCE)0733-9429(2008)134:2(274) CE Database subject headings: Bed roughness; Turbulent flow; Numerical models; Flow visualization; Flumes.

The Hargreaves method enables reference crop evapotranspiration ([ET.sub.0]) estimation in areas where meteorological information is scarce, as, for example, southern Spain. However, this method is known to produce considerable bias in this region, especially during the dry, hot summer months. An evaluation of the method is made by comparing daily estimates with those made by the more commonly recommended Penman-Monteith method at 16 meteorological stations. Computed [ET.sub.0] values at the coastal stations are, on average, 0.69 mm [d.sup.-1] smaller than the Penman-Monteith estimates whereas at inland stations a small average overestimation of 0.13 mm [d.sup.-1] is shown. The adjusted Hargreaves coefficient (AHC), obtained through regression analysis, increases at the coastal stations, on average, to 0.0029, and decreases at the inland stations to 0.0022. Adjustment with the Samani method does generally not produce more accurate estimates in this region. Finally a linear relationship between the AHC and the rate of the average temperature to the average daily temperature range is proposed for the regional adjustment of the Hargreaves coefficient. CE Database subject headings: Evapotranspiration; Calibration: Spain; Crops; Irrigation practices.

Compares the performance of four different infiltration techniques for the assessment of infiltration in a no-tillage olive orchard. Estimation of the wetting potential plot using water release curves from soil cores; Characterization of plot infiltration; Numerical analysis of the effects of tree arrangements on runoff prediction from infiltration measurements.