Block Ramp Research Articles

Surface and Subsurface Flow through Block Ramps

Block ramps are permeable hydraulic structures. Flow that enters the block ramp infiltrates between the blocks and eventually on the porous base material on which the ramp is posed. The percentage rate of subsurface flow with respect to the total flow at the entrance of a block ramp or a rock chute is studied experimentally and analyzed by means of dimensional analysis. This quantity is described as a function of related parameters, such as the total inflow discharge, the particles' characteristics, the thickness of the base material bed, the geometric characteristics of the block ramp, and the boundary conditions at the toe of the ramp itself. The experimental data were elaborated in order to supply new formulations of the flow discharge through the base ramp material and the block ramp energy dissipation. The amount of energy losses of such structures is essentially a function of the geometry and the bed surface characteristics of the ramp, the hydraulic conditions, and the percentage rate of the subsurface flow.

Sediment transport on block ramp: Filling and energy recovery

The effect of sediment transport on both morphology and energy dissipation in presence of non conventional stream rehabilitation structures, such as block ramps or rock chutes, is a not well explored topic on hydraulic engineering. Namely, in normal functioning conditions, these types of structures are generally located in mountain rivers, which are characterized by an elevated sediment transport which can be deposited and trapped between the rocks constituting the ramp. This causes a change in the bed roughness and in the energy dissipation process that is present on a block ramp. This occurrence was experimentally investigated at the Hydraulic Laboratory of the University of Pisa. Different experimental conditions were tested and the main hydraulic and geometric parameters controlling the filling phenomenon and its effects were highlighted. Namely, it was experimentally proved that both the median diameters of the filling material and of the ramp blocks, the ramp slope and the discharge are the most relevant parameters governing the ramp filling. Thus, experimental formulae were derived to foresee the ramp morphological changes and the interaction between the filling process and the geometric and hydraulic parameters. Moreover a comparison of the energy dissipation on block ramp was conducted and the energy recovery in presence and absence of filling material was compared.

Scour Control Downstream of Block Ramps

Scour control downstream of a hydraulic structure is an important topic in river engineering. A block ramp is a structure that can be built with a low-environmental impact stilling basin realized by means of a sill that controls the scour hole. The scour that occurs downstream of block ramps is analyzed and the effect of rock sills on scour geometry is evaluated. Experiments have been carried out with ramp slopes varying between 1V:4H to 1V:12H. Three different sill types were tested for a total of 300 experiments among which about 140 tests involved rock sills. Useful equations for the design of the stilling basin are proposed.

Energy Dissipation on Submerged Block Ramps

Block ramps represent structures that produce high energy dissipation and have a unique characteristic of preserving the ecological balance in a river restoration project. The energy dissipation of a block ramp changes with the tailwater level. In this technical note the relative energy dissipation in submerged flow conditions has been investigated. The experiments were conducted at the Hydraulic Laboratory of the University of Pisa, Pisa, Italy on ramps characterized by different block materials, submergence conditions, and ramp slopes. The study shows that the relative energy loss, varying the hydraulic jump location on the ramp, is essentially a function of the scale roughness, the ramp slope, the ratio between the critical water depth, and the ramp height and the ratio between the ramp length and the reduced length in submerged conditions. The differences in energy dissipation for a submerged hydraulic jump in different bed conditions are also investigated.

Scour control and surface sediment distribution downstream of block ramps

Block ramps or rock chutes are structures characterized by large bed slopes. They are increasingly used as river bed stabilization measures because of their particular capacity to sustain the river morphology and biological continuity. The scour process downstream of block ramps is an important research topic in engineering practice that must be controlled to ensure their structural stability. The purpose of this study is to analyze the scour downstream of a block ramp, in presence of a rock sill located in the stilling basin. The effect of sills is analyzed for non-uniform bed material. A dimensional analysis resulted in physically based dimensionless groups controlling the profile of the scour hole. The sediment distribution of the non-uniform bed mixtures at the scour equilibrium configuration is studied. The surface sediment redistribution is investigated for different scour typologies and the effect of protection work is also analyzed

Energy Dissipation on Reinforced Block Ramps

Block ramps or rock chutes are stream restoration structures used in many hydraulic projects. If the base material presents stability problems, a reinforcement can be used; it consists of placing over the ramp rocks greater in size than the base material in order to increase the flow resistance and reduce the shear stresses on the base material. The presence of these boulders also changes the energy dissipation of the flow over the structure. This work shows the results of experimental tests conducted on reinforced block ramps with slopes varying from 0.08 to 0.33. The effect of the various geometric parameters has been investigated. The aim is to extend existing relationships for a simple block ramp and define a new equation that can be applied to a block ramp with or without the presence of boulders.