The hydraulic bump: The surface signature of a plunging jet

When a falling jet of fluid strikes a horizontal fluid layer, a hydraulic jump arises downstream of the point of impact provided a critical flow rate is exceeded. We here examine a phenomenon that arises below this jump threshold, a circular deflection of relatively small amplitude on the free surface, that we call the hydraulic bump. The form of the circular bump can be simply understood in terms of the underlying vortex structure and its height simply deduced with Bernoulli arguments. As the incoming flux increases, a breaking of axial symmetry leads to polygonal hydraulic bumps. The relation between this polygonal instability and that arising in the hydraulic jump is discussed. The coexistence of hydraulic jumps and bumps can give rise to striking nested structures with polygonal jumps bound within polygonal bumps. The absence of a pronounced surface signature on the hydraulic bump indicates the dominant influence of the subsurface vorticity on its instability

The sharing of flood waters in the Ksours of Ghardaia and Berriane (Algeria) hydraulic study

The present article deals with two systems of sharing flood waters used in the oases of Ghardaïa and Berriane. Based on bibliographic work, and data collection and investigations performed during the period between 2006 and 2018 near the Ksourian population as the floods are the only source of water for both oases. Ancestral hydraulic systems of sharing and regularizing floods were implemented in both oases. Each hydraulic system is composed of several hydraulic structures (e.g. dams, spillways, galleries, wells) that have been designed taking into considerations the geomorphology and topography of the region. This study compares the two systems and proves that although built 7 centuries ago, both the systems were built with intelligence. They have become parts of the national heritage and must be preserved for future generations

Averaging theory for the structure of hydraulic jumps and separation in laminar free-surface flows

We present a simple viscous theory of free-surface flows in boundary layers, which can accommodate regions of separated flow. In particular this yields the structure of stationary hydraulic jumps, both in their circular and linear versions, as well as structures moving with a constant speed. Finally we show how the fundamental hydraulic concepts of subcritical and supercritical flow, originating from inviscid theory, emerge at intermediate length scales in our model.Comment: 6 EPSI figs included by psfig; 4 pages; to appear in PRL, vol.79, 1038 (Aug.11, 1997

Fluvial dynamics and watermills location in Basilicata (Southern Italy)

Watermills (grain mills, waulk mills, olive mills, sawmills and threshing machines) operated in the Basilicata Region from the Roman Period until the early decades of the twentieth century, representing an important feature of waterways that is today almost totally forgotten. Using documentary sources, ancient maps and field survey it is possible to catalogue and identify the location of these ancient hydraulic structures. Watermills were usually placed far enough away from the river to avoid inundation during floods, and near natural knickpoints or artificial steps in the river long profile that were created by mill engineers. Mill construction often had significant impacts on a rivers morphology, because it was necessary to divert the river discharge towards the mill wheel, to drive the grain-grinding mechanism. Watermill typological variations have been examined in relation to variations in river pattern to assess the ways in which the hydrographic and hydrological settings of the Basilicata Region have affected mill siting and operation. Most Basilicata watermills were built with a horizontal water-wheel and a tower. The characteristics of the tower and the associated hydraulic structures varied according to the environmental setting. Finally, mill positions define also the locations on the river system that have already been used to exploit hydraulic power and thus could be useful for future use in the micro-hydroelectric secto

Taming the Floods: Using an Intellectual History of Chinese Hydraulic Thought to Address Contemporary Issues in China’s Water Governance

China’s current hydraulic systems are in a state of atrophy, caused by sustained damage over centuries to infrastructure that has changed very little. Added to an already weak infrastructure is a relatively new crisis of water scarcity, which is forcing the Chinese government to allocate water resources between industry, agriculture, and people. As a state accustomed to water control without the context of scarcity, the state’s current governance structures are ill-equipped to solve the current crisis in sustainable fashion. The state is reluctant to approach non-traditional methods of water governance, and this resistance can be attributed to over two-thousand years of state authority over water control. This paper seeks to pose a challenge to the existing perception of modernism in Chinese hydraulic thought

Three dimensional quantification of soil hydraulic properties using X-ray Computed Tomography and image based modelling

We demonstrate the application of a high-resolution X-ray Computed Tomography (CT) method to quantify water distribution in soil pores under successive reductive drying. We focus on the wet end of the water release characteristic (WRC) (0 to -75 kPa) to investigate changes in soil water distribution in contrasting soil textures (sand and clay) and structures (sieved and field structured), to determine the impact of soil structure on hydraulic behaviour. The 3D structure of each soil was obtained from the CT images (at a 10 µm resolution). Stokes equations for flow were solved computationally for each measured structure to estimate hydraulic conductivity. The simulated values obtained compared extremely well with the measured saturated hydraulic conductivity values. By considering different sample sizes we were able to identify that the smallest possible representative sample size which is required to determine a globally valid hydraulic conductivity

Mega-geomorphology and neotectonics

For several decades, subtle neotectonic effects involving several square kilometers have been studied in detail using remote sensing, primarily various types of stereo-aerial photographs at scales of 1:10,000 to 1:80,000. These subtle effects, especially local uplifts associated with growing structures of differential compaction, have been detected by the effect on drainage patterns, changes in hydraulic geometry of individuals channels or groups of channels, tonal halos (soil) and fracture patterns. The studies were extended with the advent of thermal IR imagery particularly in tonal analysis, and SLAR primarily in fracture pattern studies. Lately, quantitative efforts have begun attempting to link measured uplift over known structures with measured changes in hydraulic geometry and alluvial deposition. Thus, efforts are now underway attempting to quantify the relationship between neo- (micro-) tectonic changes and geomorphic parameters of drainage systems

Testing of Concrete Abrasion Resistance in Hydraulic Structures on the Lower Sava River

The paper deals with the issues of resistance of concrete linings to long-term abrasion loading caused by waterborne particles, particularly for the proposed hydro power plants on the Sava River in Slovenia. The main purpose of the research work was to define the possibility of forecasting the process of concrete lining wear on the Sava River dam structures based on the standard procedures of abrasion resistance testing. Abrasion resistance of concrete has been researched in accordance with the standard ASTM C 1138 and Böhme (DIN 52108) methods. The research work was based on a comparison between laboratory results and measurements of abrasion resistance of concrete under natural conditions by performing test plots in the stilling basin of the Vrhovo HPP. Concrete composites with different mechanical properties have been analysed within the research programme. The analysis showed a qualitative similarity of the level of concrete abrasion between laboratory simulations and measurements in the field, as well as suitability of the ASTM C 1138 laboratory method for the assessment of\ud abrasion resistance of concretes in the spillway of the HPP chain on the Lower Sava River

Mitigation of flash floods in arid regions using adjoint sensitivity analysis

This paper presents an analysis of the sensitivities of flood wave propagation to variations in certain control variables and boundary conditions by means of the adjoint method. This uses a variational technique to find the relationships between changes in predicted flood water levels and changes in control variables such as the inflow hydrograph, bed roughness, and bed elevation. The sensitivities can be used for optimal control of hydraulic structures, for data assimilation, for decision makers' procedures, for the analysis of the effects of uncertainties in control variables on the predictions of floods water levels, and for investigating both the sensitivities of model flood forecasts to model parameters, boundary and initial conditions. Example of the last application of the sensitivity analysis is presented and discussed These methods are developed and implemented through a numerical hydraulic model of channel flow based on the Shallow Water Equations (SWEs) and the corresponding adjoint model. The equations are integrated using finite difference methods and a new modified method of characteristics is used to define the open boundaries. Results of validation tests on both the forward hydraulic model and on the adjoint model are presented