Benefits of Riprap
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Streets & Stormwater
Mangroves provide many valuable services: they stabilize shorelines, filter pollutants from water, allow sediment to settle, sequester carbon from the atmosphere, and provide nursery grounds and habitat for a wide range of estuarine creatures, including commercial and recreational fish species.
From an ecological perspective, mangroves are essential to the health of the ecosystem -- from their roots to their
leaves. Roots provide nursery habitat for juvenile fish, shellfish, and crustaceans by allowing them to hide from predators. These small animals feed on even smaller phytoplankton and form the base of a food chain that starts with bacteria breaking down mangrove leaves that have fallen into the water and ends with marine species that are harvested by humans.
Removing mangroves and putting in a seawall may seemingly provide increased erosion protection along with an unimpeded view. However, mangroves are adapted to withstand the strong storms and hurricanes that frequent Florida and are the ultimate erosion protection. Also, since mangroves can be trimmed to provide a view, there is no reason the long-term benefits derived from mangroves such as estuarine habitat, filtering water, protecting the land, and other values should be lost.
The over-armoring of much of the Naples Bay shoreline within the City is a major environmental issue. The prevalence of seawalls along the northern third of the bay has resulted in increased turbidity and reduced light passage through the bay’s waters. The energy in boat wakes reflects off the perpendicular walls without much absorption of that energy, keeping the water agitated and sediments constantly resuspended. Further, the vertical nature of a wall restricts mangrove establishment and does not provide the substrate necessary for estuarine shoreline community development. Both plants and animals have a hard time becoming established at such locations.
By utilizing riprap (rocky material slanted along the shoreline at a 2 or 3 to 1 slope) instead of a seawall, an estuarine community can develop within the nooks and crannies between the rocks. Riprap is an environmentally friendly alternative to seawalls. It creates a shoreline edge that can be used by oysters, crabs, fish, and mangroves. A shoreline with riprap protects the land from the erosional force of waves and efficiently absorbs wave energy because it is sloped. That, in turn, reduces turbidity and the resuspension of sediments, thus improving water clarity. Riprap is much more aesthetically pleasing than a seawall, is less costly, and requires less maintenance. If mangroves are already present along a shoreline, riprap can even be placed amongst the roots allowing enhanced protection without mangrove destruction. Even placing rocks in front of an existing seawall will alleviate some of the environmental impacts of a seawall while lengthening its life by reducing scouring effects at the base of the wall and decreasing the energy of waves pounding into it.
However, of great importance is that every one of the favorable qualities of riprap are tremendously enhanced if mangroves are planted among the rocks, plus they provide the added feature of filtering pollution from stormwater runoff. Mangroves can naturally recruit as well into riprap. Approximately a third of the shoreline of Naples Bay is armored by riprap, but only a small amount of that riprap has mangroves growing in it. Most of the Moorings Bay system is comprised of vertical seawalls with no mangroves.
The state of Florida regulates the cutting of mangroves, and the regulations addressing mangroves are cumbersome to understand. Basically, for waterfront (riparian) property owners, mangroves growing along one's shoreline that are not greater than 10 ft. in height as measured from where the root enters the mud and are within 50 ft. of the shoreline can be trimmed down to a height of no less than 6 ft. without a permit, as long as the trees maintain their leaf mass. Trimming of mangroves taller than 10 ft. must be supervised or conducted by a professional mangrove trimmer (PMT). Once the trees are legally trimmed, anyone may maintain the trim. Thus, if kept at a 6 foot height from riprap sloping down towards the water, the mangroves will be rooted below yard level and will not affect views.