Risk assessment studies considering the failure of embankment dams often require the prediction of basic geometric and temporal parameters of a breach, or the estimation of peak breach outflows. Many of the relations most commonly used to make these predictions were developed from statistical analyses of data collected from historic dam failures. The prediction uncertainties of these methods are widely recognized to be very large, but have never been specifically quantified. This paper presents an analysis of the uncertainty of many of these breach parameter and peak flow prediction methods. Application of the methods and the uncertainty analysis are illustrated through a case study of a risk assessment recently performed by the Bureau of Reclamation for a large embankment dam in North Dakota.

Since their introduction in 1993, acoustic Doppler velocity meters (ADV's) have quickly become valuable tools for laboratory and field investigations of flow in rivers, canals, reservoirs, the oceans, and around hydraulic structures and in laboratory scale models. The post-processing and analysis of ADV data present unique requirements compared to traditional current-metering equipment, due to the types of data obtained, the analyses that are possible, and the need for filtering of the data to ensure that technical limitations of ADV's do not adversely affect the quality of the results. One useful software tool for this purpose is the WinADV program, written by the author for use in the Bureau of Reclamation's Water Resources Research Laboratory, and made available to the public via the Internet since 1996. The program is designed for postprocessing of real time data files (*.adv files) recorded by SonTek and Nortek ADV's, and offers powerful filtering and processing options that make it valuable for field and laboratory studies. The software has been regularly upgraded to maintain compatibility with new file formats, and also now has limited capability to analyze data collected by SonTek's Argonaut series of monostatic Doppler current meters. This paper describes the software and illustrates the application of some of its advanced features to typical hydraulic measurement situations.

Fig. 1. True sphere and the object produced by the intersection of orthogonal circular cylinders DISCUSSIONS AND CLOSURES 484 / JOURNAL OF HYDRAULIC ENGINEERING © ASCE / JUNE 2003 J. Hydraul. Eng. 2003.129:484-487. Downloaded from ascelibrary.org by New York University on 05/15/15. For personal use only.

The jet erosion test (JET) and the hole erosion test (HET) are two tests used to determine soil erodibility classification, and results are commonly interpreted by two distinct methods. A new method based on fluid energy dissipation and on measurement of the eroded mass for interpreting the two tests is proposed. Different fine-grained soils, covering a large range of erodibility, are tested. It is shown that, by using common methods, the erosion coefficient and average critical shear stress are different with the JET and with the HET. Moreover, the relative soils classifications yielded by the two erodimeters are not exactly the same. On the basis of the energy method, an erosion resistance index is determined for both apparatuses, and a classification of surface-erosion resistance is proposed. For both apparatuses, values of the erosion resistance index are roughly the same for each soil, and a single classification of soil erodibility is obtained.

The energy-momentum ͑E-M͒ method for calibrating submerged radial gates was refined using a large laboratory data set collected at the Bureau of Reclamation hydraulics laboratory in the 1970s. The original E-M method was accurate in free flow, and when the gate significantly controls submerged flow, but for large gate openings with low head loss through the gate, discharge prediction errors were sometimes large ͑approaching 70%͒. Several empirical factors were investigated with the laboratory data, including the combined upstream energy loss and velocity distribution factor and the submerged flow energy correction. The utility of the existing upstream energy loss and velocity distribution factor relation was extended to larger Reynolds numbers. The relation between the relative energy correction and the relative submergence of the vena contracta was shown to be sensitive to the relative jet thickness. A refined energy correction model was developed, which significantly improved the accuracy of submerged flow discharge predictions. Although the focus of this work was radial gates, the energy correction concept and these refinements potentially have application to all submerged sluice gates.

A theoretically based computational model is presented for predicting the hydraulic performance of Coanda-effect screens. These screens use a tilted-wire, wedge-wire screen panel to remove thin layers of high-velocity flow from the bottom edge of a supercritical flow. Typical slot openings are 1 mm or less, and the screens are self-cleaning with no moving parts. The discharge characteristics of several screen materials were evaluated in laboratory tests, and a relation was developed for computing the discharge through a tiltedwire screening surface as a function of the Froude number, the specific energy, and the Reynolds and Weber numbers. A model for the performance of complete Coanda-effect screen structures predicts the wetted length of screen required to accept a given flow, or the flow rate through the screen and the bypass flow over a screen that does not accept all of the flow. Predictions from the model compare favorably to results from clean-water laboratory tests of several different prototype-size screen structures. The model will allow designers to accurately size screens and evaluate design alternatives.

In recent years, design floods have increased beyond spillway capacity at numerous large dams. When additional spillway capacity is difficult or expensive to develop, designers may consider allowing the overtopping of a dam during extreme events. For concrete arch dams, this often raises issues of potential erosion and scour downstream from the dam, where the free jet initiating at the dam crest impacts the abutments and the downstream river channel. A recent review has shown that a commonly cited equation for predicting the trajectory of free jets is flawed, producing jet trajectories that are much too flat in this application. This could lead analysts to underestimate the amount of scour that could occur near a dam foundation, or conversely to overestimate the extent of scour protection required. This technical note presents the correct and incorrect jet trajectory equations, quantifies the errors associated with the flawed equation, and summarizes practical information needed to model the trajectory of free jets overtopping dam crests.

Long-throated flumes and broad-crested weirs have become accepted standards for open-channel flow measurement during the past two decades. These structures offer the accuracy and reliability of critical-depth flow measurement, theoretically based calibrations, the lowest head loss requirement of any critical flow device, and extraordinary design and construction flexibility. Computer software developed in recent years has streamlined the design and calibration process. The software, WinFlume, has been described in several papers and a recent text. Although WinFlume is very easy to use, there is still a need for simplified design and calibration tools for situations where use of the computer model is not possible or desirable. This paper combines several previous efforts to provide such tools in both metric and English units for the most typical measurement applications encountered in irrigation and drainage systems. Pre-computed designs for trapezoidal broad-crested weirs, long-throated flumes with rectangular control sections, broad-crested weirs in circular pipes, V-shaped long-throated flumes, and portable RBC flumes are presented in easy-to-use tables that provide head and discharge ranges, Au cours des vingt dernières années, des canaux jaugeurs à col allongé et des déversoirs à crête épaisse sont devenus les normes acceptées pour les mesures de débit à surface libre. Ces structures possèdent l'exactitude et la fiabilité des mesures des débits de profondeur critique, des étalonnages théoriques, la caractéristique de perte de charge la plus basse de n'importe quel dispositif d'écoulement critique et une extraordinaire souplesse de conception et de fabrication. Un logiciel développé ces dernières années a simplifié les modalités de conception et d'étalonnage. Le logiciel, WinFlume, a été décrit dans plusieurs articles et dans un texte récent. Bien que WinFlume soit d'un emploi très facile, on a toujours besoin de conception et d'outils d'étalonnage simplifiés dans les cas où la modélisation par ordinateur n'est pas possible ou pas souhaitable. Cet article associe plusieurs efforts effectués auparavant pour fournir de tels outils utilisant des unités métriques et anglaises pour les programmes de mesures les plus courants rencontrés dans les systèmes de drainage et d'irrigation. Des conceptions précalculées pour des déversoirs à trapézoïdaux à crête épaisse, des canaux jaugeurs à col allongé à sections de contrôle rectangulaires, des déversoirs à crête épaisse dans des tuyaux circulaires, des canaux jaugeurs à col allongé en V et des canaux jaugeurs portables RBC sont présentés dans des tableaux faciles d'emploi qui indiquent les gammes de