As you may know, there are some portions in our planet such as those
lined channels and outlets of pipes that are potential for critical
erosion. Several studies have noted that the storm water transported
through man-made conveyance systems at design capacity is said to have
generally reached a velocity that surpassed the capacity of the
receiving channel or area to avoid erosion. With this idea, several
experts have come to consider building riprap aprons as a form of flow
transition structure needed to absorb the initial impact of flow and
lessen the speed of the flow to a non-erosive pace.
On its most basic, a riprap apron is actually an arranged layer or pile of broken rocks placed over the soil surface on slopes as well as at or below the temporary dikes or storm drain outfalls. A riprap apron is largely employed as a slope protection as it has the strength to protect the foundation against erosion and dissolves the energy of runoff or surface water flow. However, a riprap apron is not just employed for such purpose, but it is also commonly used as an outlet protection as it helps to reduce the pace of concentrated storm water flows, thereby reducing the erosion or the onset of scouring at storm water outlets.
There are generally a number of techniques necessary for achieving a potent riprap apron protection. It is typically suggested that one should employ a riprap apron or blanketed slopes, and the outlet protection should be installed at the outlets of all pipes, curves, sediment basins, catch basins, swales, interceptor dikes, and channel sections where the speed of the flow may trigger the onset of erosion in the receiving area. Moreover, a riprap apron as a form of outlet protection should be employed at outlets where the speed of the flow at the design capacity may cause plunged pools, those small and permanent pools that are usually located at an inlet or outfall.
In constructing a riprap apron, certain limitations are actually there that need to be considered. It is necessary to note that in forming a riprap apron, the minimum particle size of the rock must be sized for the maximum expected velocity of flow out of the outlet as well as the conditions of the soil where the outlet will be situated. The design of the rock must also be given attention when opting for building a riprap apron. It is somehow necessary to note that in building riprap apron, the design of rock outlet protection depends greatly on the spot. And, one must then understand that the pipe outlets at the top cuts or on slopes steeper than 10 percent cannot be protected by a riprap apron because of the re-concentration of flows as well as high velocities that are encountered after the flow leaves the riprap apron.