Scour Analysis in High Vertical Drop Shallow Using Numerical and Physical Models
The "vertical drop Structure" is one of the basic types used in channel system flow. Drops are used as slope breakers in some parts of channels where we encounter supercritical slopes. Scour is a dynamic phenomenon that is visible in vertical drop tail water depth. Because of complexity of Scour process and simultaneous testing of variables' effective compliance, studies are still underway to determine the accuracy of the equations and provide possible explanation for this phenomenon. These investigations include field or laboratory experiments under special conditions where mathematical models have been often used to provide an explicit result. Using the laboratorial physical modeling, this research explores the impact of a vertical drop flow rate on the balance of forces at the scour depth below a high vertical drop . Satisparametery results have been obtained by changing several of the parameters like sediments grading, tail water depth and flow rate. In order to specify a set of effective parameters, dimensional analysis has been used to show the scour hole dimensions. Also, computer software FLOW-3D was used to simulate the numerical modeling of Scour below a high vertical drop. The data from numerical simulation is then compared with physical modeling resulting in the great compatibility and correlation.
Scour below a high vertical drop
Experimental results on scour below a high vertical drop (drop height/critical depth >1) in uniform sands and gravels are presented. The experimental results are used to describe the effects of important parameters, identified from the dimensional analysis, on equilibrium scour depth. The important observations are that the equilibrium scour depth increases with increase in densimetric Froude number, whereas the scour depth decreases with increase in sediment size and tailwater depth. The time scale of scour depth that follows an exponential law is determined. The nondimensional time scale decreases with increase in densimetric Froude number.
Scour below an overfall: Part I. Investigation
Scour below an overfall contributes to headcut instability and gully advance. Thirteen large–scale scour tests were 
conducted by preforming an overfall in a compacted cohesive soil bed. Horizontally compacted soil layers were placed using 
typical embankment construction methods. Water flowing over a horizontal approach was allowed to plunge over an overfall 
and impinge on the compacted soil bed. Different combinations of soil moisture and soil density were examined for two similar 
tailwater or backwater conditions. For a constant flow rate, the vertical scour was measured downstream of the gully overfall, 
and typical erosion behavior is discussed. The rate of vertical scour was observed as the plunge pool deepened. 
The vertical scour rate increased as the moisture content at the time of compaction decreased. The scour rate was also 
observed to decrease as the dry density of the fill material increased. For the soil conditions tested, the vertical scour rate 
increased as the unconfined compressive strength increased. The stress–strain modulus and the vertical scour rate also 
displayed a direct relationship. The layered soil placement methods, typical of embankment construction, can have an 
influence on the observed vertical scour rates. These field–scale erosion tests were conducted to enhance our understanding 
of scour processes. This scour investigation focuses on the test description, observed results, and fundamental relationships, 
while a companion article addresses prediction methods.