Journal of Hydraulic Engineering

The correct parameterization of vegetation using measurable plant characteristics is essential for reliable flow resistance estimates. This paper focuses on the impact of density and distribution of the leaf mass on the drag force. Direct drag force measurements on flexible artificial plants were conducted in a stand. The experiments were novel in that the leaf area index (LAI) was varied in two ways: (1) the distances between the plants were altered, and (2) the leaf area of the plants was doubled and tripled. In addition, the vertical leaf area distribution was examined. The drag forces depended on the leaf mass in a similar fashion regardless of the horizontal distribution of the leaf mass, but the vertical distribution had a more significant impact. Shading of the leaves slightly reduced resistance for bushy plants because the leaf mass hidden behind the frontal projected area exerted drag. The experiments confirmed LAI to be a useful measure in estimating vegetative resistance.

This study presents findings from two-dimensional depth-averaged flow models used to investigate distributions of flow velocity, unit discharge, and boundary shear stress associated with flow around spill-through bridge abutments, a very common form of bridge abutment. Design engineers often use such flow models to determine the distribution of flow through bridge waterways and to estimate peak magnitudes of flow velocity, unit discharge, or boundary shear stress for use in design estimation of abutment scour depth. The findings show how abutment flow fields, dominated by flow contraction around the abutment, adjust in response to variations of abutment length, floodplain width, and main-channel dimensions. The adjustments alter the magnitudes of amplification factors for depth-averaged velocity, unit discharge, and bed shear stress in the abutment vicinity; amplification factor for velocity is the ratio of maximum velocity to mean approach velocity (on the upstream floodplain or in the main channel). They also alter the distance from the abutment toe to the locations of peak values. This study covers a much broader range of abutment lengths, floodplain widths, and channel dimensions than heretofore reported in the literature.

An experimental campaign of 21 long-duration tests on scouring at complex piers of different configurations was performed to investigate the effect of pile cap thickness on the temporal evolution of the maximum scour depth and the development of equilibrium conditions. Two test series were performed with two significantly different pile cap thicknesses over a wide range of pile cap elevations with respect to the expected scour hole and the approach flow depth. In addition, the accuracy of existing methods to calculate the maximum scour depth was evaluated and discussed. The results show that, in general, the thicker the pile cap, the deeper the corresponding scour hole. The increase in scour depth that is attributable to the pile cap thickness depends on the distance between the pile cap and the original bed level. The observed maximum scour depth was greater with the thicker pile cap (with respect to the thinner pile cap) when it was entirely immerged into the flow, partially buried, or totally buried at a small depth from the initial bed level. Depending on the distance between the pile cap and initial bed level, the pile cap thickness may also influence the temporal evolution of the maximum scour depth by increasing or reducing the scouring rate.

Hurricanes in southeastern Louisiana develop significant surges within the lower Mississippi River. Storms with strong sustained easterly winds push water into shallow Breton Sound, overtop the river’s east bank south of Pointe à la Hache, Louisiana, penetrate into the river, and are confined by levees on the west bank. The main channel’s width and depth allow surge to propagate rapidly and efficiently up river. This work refines the high-resolution, unstructured mesh, wave current Simulating Waves Nearshore + Advanced Circulation ($\mathrm{SWAN}+\mathrm{ADCIRC}$) SL16 model to simulate river flow and hurricane-driven surge within the Mississippi River. A river velocity regime–based variation in bottom friction and a temporally variable riverine flow-driven radiation boundary condition are essential to accurately model these processes for high and/or time-varying flows. The coupled modeling system is validated for riverine flow stage relationships, flow distributions within the distributary systems, tides, and Hurricane Gustav (2008) riverine surges.

Methods for quantifying the uncertainty in discharge measurements typically identify various sources of uncertainty and then estimate the uncertainty from each of these sources by applying the results of empirical or laboratory studies. If actual measurement conditions are not consistent with those encountered in the empirical or laboratory studies, these methods may give poor estimates of discharge uncertainty. This paper presents an alternative method for estimating discharge measurement uncertainty that uses statistical techniques and on-site observations. This interpolated variance estimator (IVE) estimates uncertainty based on the data collected during the streamflow measurement and therefore reflects the conditions encountered at the site. The IVE has the additional advantage of capturing all sources of random uncertainty in the velocity and depth measurements. It can be applied to velocity-area discharge measurements that use a velocity meter to measure point velocities at multiple vertical sections in a channel cross section.

The known formulations for steady-state hydraulics within looped water distribution networks are rederived in terms of linear and nonlinear transformations of the original set of partly linear and partly nonlinear equations that express conservation of mass and energy. All of these formulations lead to a system of nonlinear equations that can be linearized as a function of the chosen unknowns using either the Newton-Raphson (NR) or the linear theory (LT) approaches. This produces a number of different algorithms, some of which are already known in the literature, whereas others have been originally developed within this work. For the sake of clarity, all the different algorithms were rederived using the same analytical approach and a unified notation. They were all applied to the same test case network with randomly perturbed demands to compare their convergence characteristics. The results show that all of the linearly transformed formulations have exactly the same convergence rate, whose value depends on whether a NR or LT algorithm was used, and that they converge faster than the nonlinearly transformed formulations do. A number of computational factors suggest that the global algorithm, in either its NR or LT form, is the most attractive of the various formulations to implement.

In last three decades, the reliability of water distribution systems (WDSs) has become a major concern, not only for water utilities and academic research communities, but also for society as a whole. Notable research has been conducted on the reliability/availability of WDSs, however, little attention has been paid to quantify the impact of adaptive operations as a response to system failure to enhance the resiliency of WDSs. Here, resilience is defined in the general sense as the ability to recover from a failure to a satisfactory state. In practice, if a system fails to supply water with adequate pressure, the water utility would take action to respond. Adaptive actions include switching on additional pumps as a short-term remedy or maintaining a higher water level in storage tanks as a long-term strategy to satisfy system pressure when a system experiences abnormal conditions. Here, a Monte Carlo simulation based framework for the resilience analysis of WDSs is implemented, considering the impact of adaptive pump operations and isolation valve locations. The framework consists of four steps: (1) random event generation for nodal demand fluctuations and pipe breaks; (2) identification of isolated segments based on valve layout; (3) hydraulic simulation with regular and adaptive operations; and (4) identification of responses and the evaluation of system resilience/availability. The proposed methodology is applied to a mid-sized WDS and results show that adaptive pump operations improve system resilience with a moderate pumping cost increase.

The Dujiangyan Project is a World Cultural Heritage Site with relevance to water conservancy. It has been operated for more than 2,260 years and still plays an important role in irrigation, urban, and industrial water supply, flood control, and tourism. This paper discusses the hydraulic principles of the project, focusing on the reasons for the longevity of the project. In particular, two aspects of the project are reviewed; namely, the practical engineering design of the project and its outstanding historical significance and time-based maintenance. The project ingeniously used the topography of the terrain in the design of weir structures. The tasks of water diversion, irrigation, and flood control were achieved using a two-step approach. The first step was achieved by utilizing the shifting of streamlines and the bend of flow from the town of Guankou to Fish Mouth (a diversion embankment). The discharge of flow and sediment was further optimized by using the second step of combined control of Feishayan (a sediment and flow spillway) and Baopingkou (an irrigating gate). The bend of flow within the Inner River forces the surface water to flow into Baopingkou, whereas the bottom sediments and pebbles discharge from Feishayan. Dynasties throughout history attached great importance to the management and maintenance of the project. Retrofitting and time-based renovation prevented the abandonment of the project due to sediment accumulation and aging of building materials. Because the maintenance and operation costs were far lower than the economic, social, and ecological benefits the project had brought, the Dujiangyan Project was sustainable over the long term. The study of the engineering design and maintenance rules of the Dujiangyan Project has value for the design and construction of modern hydraulic projects.

This work deals with the simple shear flow of neutrally buoyant, rigid, frictionless spheres immersed in a viscous fluid that exchange momentum through inelastic collisions. It is shown how kinetic theories are able to provide a full analytical description of the flow, once the influence of the viscous fluid is taken into account in a simple way through the dependence of the collisional coefficient of restitution on the Stokes number. This allows the capture of the characteristics of the experiments performed by Bagnold 60 years ago and the interpretation of the macroviscous and inertial regimes described by the same author as the limits for the coefficient of restitution equal to zero and to the value valid in absence of the viscous fluid, respectively.

The question of whether wing dikes (bank-perpendicular river training structures or groynes) cause higher flood levels has been debated in the United States for many years. Some researchers point to empirical data that show large stage increases which are associated with wing dike construction, whereas other researchers have suggested that such increases are contrary to engineering theory. In a recent report, the U.S. Government Accountability Office (USGAO) presented this question as a priority to be resolved by engineers and scientists. As a first step to better understand the connection between navigation structures and flood levels on the Middle Mississippi River (MMR), a simplified theoretical analysis is presented to test the assertion (made in the USGAO report and elsewhere) that such increases are contrary to hydraulic theory. This analysis predicts that wing dike construction may lead to water level lowering for in-bank flows and to water level increases for out-of-bank (flood) flows. This confirms that, in principle, wing dikes may have contributed to the observed flood water level trends in the MMR. More detailed follow-up studies are required to accurately quantify the impact of wing dikes on flood levels.