One of the most common problems is not only a deteriorating spillway structure, but one that does not have sufficient capacity to adequately pass major storm events. At the end of the spillway a “splash pad” is used to break up energy from heavily flowing water to prevent erosion. This consists of large stones usually grouted in place to prevent shifting or movement. 

Riprap is a term for large stone that has been crushed so it has rough, jagged edges. This type of stone keys together to prevent movement. If at the end of a spillway these stones might be grouted in place to ensure no movement no matter the storm event (Also known as a splash pad).