(light music)
(bright music)
- Generally, good streams
don't become bad streams by themselves.
What happens when we attempt to control the stream
without understanding its natural tendencies?
(bright music)
So generally, good streams don't turn into bad streams
by themselves.
Problems occur when we attempt to control
the natural tendency of the stream
with concrete or other manmade materials
that confine the stream and completely stabilize the bank
such as with this channel right here.
We're talking about various hard surface control techniques
such as concrete, riprap,
gabions, and culverts.
As our cities have grown, we have often tried
to control streams by encasing them in concrete.
The concrete may control the stream right at that location,
but it often causes problems elsewhere,
both upstream and downstream.
But as the water moves through here,
the velocity is increased, we get lots of, lots of energy.
And that's fine this is moving through the channel.
But then we reach the end of the channel,
we have this high energy.
And the water moves out of the channel
and it moves into the area where we have soil,
and you often have to try to reinforce this
with big chunks of concrete or other rocks.
As it continues to move downstream,
there's still lots of, lots of energy hitting that far bank
and we're getting lots of erosion,
lots of soil loss from that area.
That continues down the channel,
then meets another main channel on that high energy,
the high flow is still there,
we're getting our downcutting,
and our erosion and our habitat degradation
in those areas as well.
That's all the result of this concrete channels
that move water quickly off the landscape into our streams.
Lining a stream in concrete
can cause more problems than it solves.
And it's not just concrete.
Look around at cities and urban areas,
you'll see many impervious services.
Big stretches of asphalt, rooftops,
and even compacted dirt roads and parking lots
increase the flow of water into the watershed.
These hard surfaces cause another problem,
and that's increased velocity.
A smooth concrete channel allows the water
to build up velocity,
increasing the downstream erosion potential,
and impairing habitats for fish and other aquatic animals.
So to understand why confining water
in a concrete channel or a culvert may cause more erosion,
let's think about washing our car with a garden hose.
If you take your garden hose with a normal flow
and run it over your car,
you may or may not get all of the dirt off your car.
You take your thumb, put it over the garden hose,
and lessen the amount of variant
that the water flow through,
the velocity increases, the force increases,
and it's probably gonna wash all the dirt off your car.
And the smaller space for the water,
the harder and faster the flow.
Erosion is when the force on the stream bottom material
is greater than the cohesive forces of the material.
Every concrete channel is going to constrict
the flow of a stream at some point over its course,
particularly during a heavy rain event.
The water speeds down the concrete with no opportunity
to spread out or slow down.
Natural streams and rivers have floodplain.
This is the area adjacent to the stream.
During heavy rains, water rises up and spreads out
over the floodplain, slowing it down.
The floodplain is a critical component of the stream system
that dissipates energy during floods
and reduces problems downstream.
A heavily eroded stream can become detached
from its floodplain through a process called downcutting.
Downcutting is when swift water erodes the stream bed,
creating a deeper channel.
At the same time, the sides of the stream begin to erode
in a process we call widening.
Widening can occur from the detachment of particles
from the stream bank, or very quickly from mass wasting,
or large chunks of soil
are lost to stream during high flows.
So there're stream downcuts and widens
as a result of the erosion process
that're growing on during our storms.
It's detached from the floodplain
which can cause a lot of issues, including loss of land
which is very important for our landowners.
- I believe that one, and one particular,
and it wasn't a huge flood, but in one shot,
I think we lost over 50 feet two or three years ago.
And it may continually going downhill literally.
- [Jason] This erosion almost wiped up the road
along the river and threaten the riverside park.
- Well, overall, this side near our park,
we had a sheer drop-off,
and we had dangerous trees in the water
where you couldn't hardly get a canoe in or out.
Not a very good environment for recreation.
- [Jason] The erosion makes the river less accessible
and further detaches it from the floodplain.
- It affects the quality of fishing, boating on the water,
and it affects downstream water quality
because all of this water carries sediment downstream
to other properties and to lakes and reservoirs
where we may have some problems there with water quality.
- [Jason] When sediment washes away
from landscapes or farmland,
it brings with the nutrients and other materials
that act as pollutants in the stream.
In addition to sediment being a pollutant in and of itself,
many of the pollutants that come off our landscape
like to stick to sediment,
so as we have an increased sediment load
coming down the stream,
that sediment will be moved downstream,
in Oklahoma, most of our streams lead to a reservoir
that are often used for recreational purposes
and for drinking water and lots of other uses.
The increase in contaminants,
such as nutrients and heavy metals,
will degrade the quality of our downstream reservoirs,
causing conditions like algae blooms
and decreasing the quality of our drinking water.
- We work with nature,
we don't try to resist the forces
that nature naturally has moving through meandering valley.
I actually work with that
and we allow those forces to create the scouring areas,
the pools, provide the riffles around the glides.
But we recognize that there're processes
that we can help with.
- [Jason] Coming up in our next segment,
working with nature to manage creeks and streams.
(bright music)