This Earthcache will bring you to a shoreline protection system referred to as riprap, rubble, shot rock or rock armour. It is rock or other material used to protect shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion. It is made from a variety of rock types, commonly granite or limestone, and occasionally concrete rubble from building and paving demolition. It can be used on any waterway or water containment where there is potential for water erosion. Shoreline Erosion Shoreline erosion, caused by the repeated pounding of waves against a shoreline, is a major problem on Prince Edward Island (PEI). The coastline of Prince Edward Island is characterized by easily erodible sedimentary rock, composed mostly of sandstones and clay stones. Average shoreline erosion rates vary from 0.5 meters (1.6 feet) per year on the south and east shores of PEI to as much as 1.5 meters (5 feet) per year on the north and west shores. The higher erosion rate on the north and west coast is directly attributable to the high degree of exposure to storm conditions. There are four ways waves can break down a shoreline: 1. Hydraulic Action This occurs when air within the cracks in the shoreline material compress from the force of the water on it; as the air compresses, it loosens the material so that repeated pounding breaks the material free. 2. Attrition This action occurs when loose material carried with the water collides with the shoreline, grinding and chipping each other, causing the material to become smaller and smaller and allowing the material to be easily carried away. 3. Corrasion This occurs when material from the shoreline breaks free and then is used to further erode the shoreline again. [the difference between attrition and corrasion is the source of material –attrition is material from elsewhere while corrasion is local material] 4. Corrosion This form of erosion occurs not on the wave action but is based on the pH level of the sea water. It occurs when the pH level of the sea is below neutral 7.0. When this occurs, particularly at high pH levels, rock is corroded away. Wave action then takes part by removing the corroded material. Riprap works by absorbing and deflecting the energy of waves before they reach the defended structure. The size and mass of the riprap material absorbs the impact energy of waves, while the gaps between the rocks trap and slow the flow of water., lessening its ability to erode soil or structures on the coast. Where the shoreline is of a very light and soft material, a fabric is often placed under the rock so that the water can’t carry away the underlying material. The mass of riprap also provides protection against impact damage by ice or debris, which is particularly desirable for bridge supports and pilings. Riprap is also used to protect the base of old Edwardian and Victorian sea walls, which being vertical, are often undermined. The riprap absorbs the impact of the waves as they shoot up the wall and then fall back down. To claim this earthcache, you must perform the following: 1. Determine which erosion action would take place here if the riprap wasn’t installed. (check the existing shoreline) 2. What type of rock is placed here to lesson the wave’s energy? 3. Take a picture of yourself and/or GPSr with the riprap in the background (optional) Do NOT post your answers, encrypted or otherwise, on your log. Do NOT log as a find until you have forwarded the answers for this EC. Failure to answer required questions through e-mail will result in a log deletion without notice.