What is Riprap

Alternative spellings and terms: rip rap, rip-rap, rock armor

You often see the shores of lakes, ponds, rivers, and other waterbodies lined with piles of rock to prevent erosion, protection for manmade structures, or just to give some sense of order to a shoreline.  These rocks are called riprap.  Rocks are stronger than soil, or sand and so reduce erosion from waves and ice, but they come with a number problems.  Although in landscaping riprap is usually composed of locally available rock, it can be specially formed concrete, or broken up concrete, bricks or other debris from demolition.   

Pond Shoreline Riprap
Rock riprap prevents erosion of the shoreline of ponds when shallow rooted turf grasses are grown up to the water’s edge. All the spaces between rocks provide some hiding places for animals it can also trap and kill small turtles

Benefits of Riprap

Not all is bad when it comes to riprap.  In very high energy situations it reduces the erosion of shorelines.  This reduces sediment and nutrients that enter the surface water.  When in the water these pollutants would block light, smother plants and animals and fuel algae blooms. 

While rip-rap can be a deathtrap for some animals, the spaces in the rocks can provide some hiding places for frogs and small mammals.  In the water riprap it can provide a unique habitat for insects, crayfish and other invertebrates. 

Habitat can also be protected with the aid of riprap.   In my area the Lake Winnebago system has seen catastrophic sedge meadow wetland loss due to high water levels from dam construction.  Well over 10,000 acres of floating wetland mats have ripped out, floated into open water where it disintegrates.  Lining the wetland with rock armor has stopped this type of erosion, but also prevents the natural interaction between wetland and lake.  Still it is much better to have wetlands, than shallow, turbid open water that has largely replaced them.

Riprap is preferable to seawalls.  As their name implies a seawall is a vertical, or near vertical hard structure on the shore of a lake or river.  Seawalls are constructed of concrete, stone, metal, or wood.  Seawalls offer the ultimate in shoreline protection, but they also direct the power of the waves back into the lake where they can erode the bottom sediments.  Seawalls prevent turtles, frog, muskrats, ducklings, and other critters from getting out of the lake, and can be detrimental to wildlife populations.  Seawalls also provide no places for young fish and invertebrates to hide. 

Negative Aspects of Riprap

Riprap has many negative attributes deriving from the fact that it is just plain unnatural.  Rocky shorelines do occur in nature, but soil and the roots of the local vegetation are usually intertwined with the rocks.  The gaps between rocks in riprap can permanently trap turtles, particularly hatchling turtles as they move from nest to water.  Riprap creates a barren landscape at shorelines that otherwise well vegetated.  This natural vegetation is often enough to prevent most erosion, while at the same time providing valuable habitat for many species of wildlife.

Overuse of riprap also increases channelization of rivers and  prevents the formation of unique habitats such as oxbow lakes and ponds. Rivers are meant to wander!   The high piles of rock can prevent flood waters from flowing from rivers into adjacent wetlands that help store the excess water.  The same flooded wetlands are visited by fish such as Northern Pike which spawn there.  Riprap can prevent the migration of these spawning fish.

Whether installation of riprap is necessary or not it can be improved to lessen its negative impacts. The easiest of this is to use smaller rocks to fill the gaps between the large ones where turtles can become trapped.  Planting native plants, or allowing the riprap to become colonized with native vegetation wipes out many of the negative impacts.

Riprap Maintenance

Like any manmade structure riprap requires maintenance.  The heavy rocks can sink into the soft sediments in the water or the water soaked shoreline soils.  Ice, waves and plain old gravity will pull the rocks into the lake or river over time.  Local governments and natural resource agencies may look at this movement as filling in of a body of water and may require the landowner to remove, and re-pile the riprap to its original location.  Placement and movement of riprap maintenance is regulated by state and federal statutes in many situations. 


I think in many situations riprap is helpful, or even necessary, but far too often it is installed because people think they need it or because it just looks nice.  It is difficult to change the minds of those who like the order and simplicity of manicured lawns and squared off properties.  Only those with a keen interest in nature may come over to the disordered beauty of natural shorelines.


Riprap can be interesting too.  In my hometown of Oshkosh, Wisconsin the lumber mills that formed the early industry of this city are long gone, but many of the foundations of those mills are broken and dumped along the edge of the Fox River and Lake Winnebago where they protect the shore from wave and ice erosion.  In some cases the concrete contains the remains of even older industry.  I once found a broken marble sink that was thrown into the concrete when it was formed. Our riprap contains evidence that our society even throws away its industry, but now I’m going off on a tangent.   

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Swamp Aerial Video

I just finished editing and uploading my last video from last summer.  This aerial video is a low altitude flight over a wetland in NE Wisconsin.  It is late September and the leaves of the trees are just beginning to change color.  Many of the trees in view Green Ash and a number of other species whose leaves turn a shade of yellow.  Not as stunning as a northern hardwood forest with maples and other trees, but still a sight to behold.

So that’s the last of the summer videos.  I’m looking forward to doing many more this summer. I hope you enjoyed this one.  Thanks for watching.

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Spring is Coming!

Dagget's Creek Meltwater

Daggett’s Creek filled with melt water from farm fields.

This week the temperature was warm and the kids were in school, so I took the opportunity to get outside and enjoy the sun after a very cold February. I hope to be getting out a lot this year to experience more of nature and work on my photography, so I am adding a new feature.  It is sort of review of the previous week, largely in photographs that will show what is happening in the natural world.  It may be only a photo or two by the time December rolls around, we shall see, but it should be rather rich in the warmer months.

High Cliff State Park Panoramic

Panoramic view from the observation tower at High Cliff State Park

This week I visited High Cliff State Park near Sherwood Wisconsin.  High Cliff features the ruins of a lime kiln used to bake the local limestone to produce lime to make cement.  The old ruins are home to a number of European Starlings, and this day they were calling and singing from small trees growing on the top of one of the old stone building.  The video below show the silhouette of the birds, and sounds of their calls with a few other species in the background.

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Drainage Ditch Flight

Latest edit of a low altitude flight over sedge meadows I made last June.  These ditches run through Poygan State Wildlife Area in Wisconsin.  Some were dug to help drain nearby farmland and some were dug decades ago for ducks and other wildlife.

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Cooper’s Hawk on Birdfeeder

Cooper's Hawk

Cooper’s Hawk (Accipiter cooperii) on the Birdfeeder

The Cooper’s Hawk (Accipiter cooperii) has become a much more common site in urban areas in my lifetime.  The Cooper’s Hawk feeds almost exclusively on other birds so the House Sparrows and other common city birds are great food source.  We often feed these birds, which no doubt increases the population size.  The population of small birds then attracts and feeds the Cooper’s Hawks, so we indirectly feed those too.

The Coopers Hawk is well adapted to hunting fast moving birds in trees.  They have relatively short wings to fit through the tree branches and a long tail that allows it to change direction quickly and sharply.

Not long ago these hawks were shot, and poisoned by DDT, which greatly reduced their numbers.  Today their populations are on the rise because of the end of those practices and somewhat our feeding of the little birds.

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Frog on Ice

A couple of days ago I took a walk down by a small spring-fed creek.  The air temperature was about 4°F (-16°C), but since the creek is fed by numerous springs the stream was nearly free of ice.  Winter time in one of these spring-fed trout streams is really interesting.  While all the world around is in a deep freeze life goes on in the water.

Frog on Ice

A Green Frog was crawling around both in and out of water in below freezing temperatures. The spring-fed stream stays warm enough to keep many different animals active all winter. Notice the freshly killed flying insects on this cold day in February.

While I was taking photographs next to the stream I saw a Green Frog crawling through the shallow water of a muck filled back water of the stream where spring water seeps up through the ground.  The amphibian was half in the water and half in the cold air where condensation had froze into hoarfrost on old grass stems only millimeters above the water’s surface.  No hibernation for this frog. The frog was very cold, and when I approached it just got down low in the mud and stayed still.  I took some photographs while trying to keep my winter pack boots from overfilling with water and mud.  I got a few different angles and so I left the frog in peace.

I made my way back to shore and resumed my photography.  A few minutes later I happened to look down at my bootlaces and found them to be encased in ice.  Later when I got back the car I tried to get them off, but couldn’t untie the laces.

Even though a Wisconsin winter is bitter cold at times the aquatic insects are still busy eating algae, detritus and each other.  Some of these stream invertebrates are so bold as to grow wings and fly in February.  When I looked at the photo of the frog later I could see to tiny flying insects lying dead on the surface of the water.  It may seem odd that insects would try to fly in the winter to mate, but in makes sense.  In winter there are very few birds around, no bats and no aerial insect predators like dragonflies.  The winter hatching insects must brave the cold, and I wonder if the ones I found suddenly froze to death just above the water’s surface.

After my visit to Emmons Creek I went to another larger, but mostly frozen over trout steam, where  I took this underwater video of the Waupaca River.

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What Good is a Grass Fire?

Cattail Marsh Fire

Flames reach for the sky as a cattail marsh burns out of control.

The benefits of fire may be somewhat obvious, but there are others we forget today.  People throughout the world have used fire to alter their environment to their benefit.  On a small scale traditional fires may have cleared a portion of forest for a garden, but hunter gathers may have changed a few acres to tens of thousands to their benefit.

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Lake Poygan Time Lapse

While my son and I were working hard at harvesting phragmites for transplanting I set up my GoPro Hero 3+ on a tripod to record some time lapse footage of the marsh and sky.  When it came time to plant the phragmites I did the same at the West Bay Cane Beds.  The weather was nice for both the harvest, planting, and shooting time lapse video.  The temperatures were relatively cool for July, and there was a little breeze.  All around tree swallows swooped catching insects on the wing, while red-winged blackbirds hurried off with a destination in mind.  As the evening wore on we kept an eye on the sky not only because it was interesting, but also because it threatened to rain.

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What is Detritus?

Sedge Meadow Leaf Litter

Leaf Litter from previous growing seasons is the main source of detritus for this sedge meadow.

Detritus is debris or waste of any kind.  When we think specifically of detritus in lakes and wetlands we think of the undecayed organic matter of plants and animals.  It is this that is typically the main source of nutrients in a body of water.  The source of detritus can be organisms the grew within the lake, or those that came outside it.

Outside sources of Detritus

Erosion can bring in all kinds of organic matter, usually from plants.  Depending on the location of a body of water or wetland the main source can be quite variable.  In a river with a large floodplain the main source may come from when the river overflows its banks and picks up organic matter from flooded wetlands, farm fields and woodlands.

A small lake, or rivers big and small in a forested setting may get most of their nutrient inputs as leaf fall.   The leaves of overhanging trees land in the water, sink and aquatic organisms begin to break them down.  First come the “shredder” invertebrates.  These are able to shred tough leaves into smaller pieces that they eat, or the scraps are eaten by others.   Then an assortment of other invertebrates continues to eat the smaller sized pieces, or the microorganisms that further break them down.  Without this source of nutrients many streams would be sterile.

Detritus in Stream

Detritus at the edge of Emmons Creek in February consists of fallen leaves, and emergent plants growing along the bank.

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West Bay Cane Bed Flight

The West Bay Cane Beds in Lake Poygan have been in decline for decades, but the last decade has been particularly unkind.  The beds are rapidly eroding from wave and ice action.  The beds are now so small that a hand full of muskrat families are eating much of what remains.

I flew a small drone over the vegetation to document its current sad condition and to compare with some past air photos.

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