All recommend re-vegetation rather than installing rock or walls, whenever possible, to keep river from speeding up & damaging downstream banks, and to protect habitat along the shore line.
Simple overview from Canada: vegetation, rock slopes, retaining walls, Living by Water Project
Gabions: rocks in rectangular cages made of aluminum mesh, so they can be stacked like gigantic bricks at & behind shoreline. Spaces among rocks may dissipate wave energy better than a solid wall does. Cost is high to put heavy rocks into the cages.
Another method is to staple Turf Reinforcement Mats (or here or here) on the bank (about $3 per square yard or square meter plus labor). They hold soil while plants grow through them, and then they support plant stems against erosion forces. You can combine them with rock (rip-rap) or gabions by mixing dirt among the stones of riprap or gabions, seeding it, and protecting it with Turf Reinforcement Mats while the plant roots spread through the dirt. This gives the strength of rocks with the habitat and water-slowing benefits of vegetation.
Here is a clear comparison of several methods: anchored tree trunks, tied bundles of dead brush, bundles of living brush, live cuttings, dead branches, polypropylene mat in water simulating sea grass, stone at water line, stone on whole slope (River Banks & Buffers No.3 - Streambank Stabilization Methods for the Connecticut River Watershed by Connecticut River Joint Commission of New Hampshire & Vermont)
A rarely used and promising method cited by the Connecticut River flyer above is to add artificial mats of fronds (artificial filaments attached to bottom, like sea grasses) in the water at the bottom of the banks. A power company used them in 1993 at the bottom of a steep slope 40 feet out in the Connecticut River, and they successfully captured sediment and created a shelf going 25 feet toward the center of the river. Friends of the Earth says they were successful at Cape Hatteras in 1981-2 until they were washed away by violent forces (on the following site, scroll to "Frond Mats" near the bottom http://www.marinet.org.uk/coastaldefences/canute.html ). They might last longer on a river, or a less stormy spot. The UK Department for Environment calls them a "best practice" for ocean use:
Maryland has thorough specifications of many techniques, Maryland's Waterway Construction Guidelines
Minnesota has flyers on:
Bluffs: drain & install riprap
Creating & managing a beach, limiting boating damage
Landscape planning along a shore
Re-vegetation is described in Alaska Streambank Revegetation and Protection: A Guide for Alaska
A study near Walnut Grove, California, used straw bales wrapped in coconut fiber (coir). They were stacked in the water, at the mouth of a scallop or dent in the shoreline; the scallop's mouth was 4.5 yards long (measured along the stream) by 6 yards from mouth back to the apex. Waves lost 60% of their energy while traveling through the bales to the protected water behind them. However straw decays fast.
Good studies are rare. Please send any citations you find to web@BoatWakes.info
Everywhere has different rules about installing protection. The following is a general outline for the United States, but this is certainly not legal advice:
ON THE WATER SIDE OF THE ORDINARY HIGH WATER MARK:
Permits generally are needed from the local government (e.g. floodplain rules), and state government (e.g. environmental permits), and the US Army Corps of Engineers. These groups usually have simple permits for small projects.
ON THE LAND SIDE OF THE ORDINARY HIGH WATER MARK
(This is for information, but if you want to prevent damage from waves in the water, you need to put protection where the waves hit, below the high water mark, so you need permits as described above):
Live Vegetation: permits generally are not needed to plant vegetation on your own property, above the ordinary high water mark. If you cultivate a large area, be sure rain doesn't wash mud into the water, which suffocates plants, fish & other small creatures, and which may have penalties.
Non-living Materials (rocks, concrete, wood, straw bales, etc.): permits generally are needed from the local government (often floodplain rules), and state government (often environmental permits).
The definition of ordinary high water varies among governments, and some use other terms. The US Corps of Engineers and EPA define it as
"33CFR328.3(e) The term ordinary high water mark means that line on the shore established by the fluctuations of water and indicated by physical characteristics such as clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas."
This is not the highest point which the water reaches, and it is not the highest annual level or any other specific frequency. Many rivers and shores have gages which record the water level continuously for years at a time (see examples and world tide gages), so one can find the highest point ever reached, or the average or half way point, or the 75th percentile, but the definition is based on appearance of the ground, not how often water reaches this level.