HYDRO21865

• Permit No: M1985026
• IBM Index Class Name: Hydrology
• Doc Date: 10/28/1985
• Doc Name: CHALLENGER PIT - FN M-85-026
• From: TUTTLE APPLEGATE RINDAHL INC
• To: MLRD
• Media Type: D
• Archive: No

The Concept of Degradation
A river system can be in one of three states:
1. Aggradetion
2. Equilibrium
3. Degradation
All river systems are constantly working to reach
equilibrium. In other words, the amount of sediment
into a reach of a river is equal to the amount cap
that reach. Sometimes, changes introduced into a =
can throw off the balance that exiata and cause tt
reseek this theoretical state of equilibrium.
construction of a dam or a lake might cause a is
of equilibrium.
The Big Thompson River in this reach can be conaid
close to equilibrium as is possible in the real worl
no evidence of either aggredation or degradation
reach. The elope of the river channel appears to
constant. There is no evidence of scouring or
sediments that would exist if it waa not in equllibr
visual inspection of the water indicates that t
large amount of either bed loud or suspended sad
river as it currently flows. The suspended aedim
exist can be partially attributed to irrigation re
the arse. A grab sample was token from the alto and
certain water quality parameters. The results of
ere contained 3n the Appendix.
If a stream channel is in a state of degradation,
to reach a state of equilibrium by removing all aedi
transportable end leaving a layer of sediment t
moved either by the tractive force of the water or
mechanical bonds. Thia phenomenon is called str
Once a stream has left a layer of sediment particle
thick, that are not moveable by these forces, then t
armored itself end will not degrade any further un
of equilibrium is changed again. A stabilized river
to return to it's original elope prior to diaturban
was in a state of degradation at that time also. T
degradation is expected, the amount can be calculate
material must be removed to leave an armor coat.
e state of
transported
ried out of
fiver channel
e stream to
Hence, the
mporary loan
red to be as
There is
in the study
be remaining
epoaition of
um. Also, a
ere is not e
went in the
nt that does
urn flow in
analyzed for
hie analysis
it is trying
ant that is
et cannot be
by electro-
am armoring.
one layer
e stream hen
it the state
bed will try
e, unless it
erefore if
by how much
The creation of a lake along this river has some limiting
factors to consider prior to reaching conclusions bout degrada-
tion downstream of the outlet. The trap efficien y of the lake
and volume of storage are important parameters. In this case,
there is no controlled outlet release such a exiata in a
reservoir with a dnm.