This is a quote from Dan in another thread, but I thought it could be really handy in this one as well.
The other "study" I think they(environuts) are quoting now and have many times in the past is the FS report done by Harvey in 1999.
Click to view attachmentIf you have not yet read this one, you should....very interesting.
And from here we will work back toward the fish and being harmful to them or not.
Ok, so we aren't lawyers (well most of us aren't) and most of us are not fish bioligists either.
Anyone know what scour is? How about redds.....what defines those?
Hmmmmmmmmmm...........
Well we kinda need to know those things as you see reading all this stuff.......because we are apparently destroying these and changing the entire ecosystem with a hand held nozzle!
So.....lets see we need to find some definitions. Here is a link that seems really informative on the topic of spawing salmonid.
Spawing Salmonid -
From that page I found several interesting tidbits........
For Coho salmon (often used as the mentioned endangered species) the water depth is an average of 4-8 inches in redds.
Gravel size used for redds will be 5.4 inches or smaller.
And the most noticable tidbit.........
TIGHT SEDIMENT IS UNSUITABLE FOR REDDS!Ok so what is scour then.......this definition can be found in the FS Harvey99 study.
"Net scour is the difference in streambed elevation between the start and the end of the measurement period (assuming elevation decreases)."
As you read through the FS Harvey99 study you will notice the scour period measured was over half a year to cover "high water season" .....not dredging season. They did however study areas that included dredged tailings.
This quote is what they said about redds in the tailings areas.....
Quoting FSHarvey99.....
"Replication ranged from three to seven within a particular combination of stream, year, and substrate (tailings versus natural substrate). In general, replication was limited by the number of redds on tailings. We readily detected redds on
natural substrates because less periphyton covered redd materials compared with the surrounding substrate.
This difference was less apparent for redds on recently created dredge tailings, and low stability of material in tailings often yielded redds
with less strongly mounded tailspills compared with those on natural substrates. For these reasons, redds on tailings were often difficult to identify in
the absence of direct observations of spawning fish. After locating as many redds on tailings as possible, we haphazardly selected an equal number
of redds on natural substrates by making measurements at the first redds we encountered either upstream or downstream of the redds on dredge tailings."
So again, large scale dredge tailings are being studied not anything small scale.
Larger equipment would of course move larger boulders.....and yes more material.
Will your dredge suck up a 5.4 in or bigger rock?
Funny though......I think they stated that they could in fact
NOT FIND THE REDDS UNLESS FISH WERE ACTIVELY SPAWING......So they haphazardly chose (guessed) with an average of the closest they could find off the tailings.
Ok so now we have a few more details on what we are supposedly destroying or will destroy.
What I saw was that tight, over compact soils are not suitable for redds.
As well......large boulders in large areas without sediment are also unsuitable. eggs need flowing oxgenated water with garvels to hold the eggs, but yet the sediment needs to be large enough for the fry to swim up and out after hatching.
The female fish when making the redd can only pick up with her tail gravels and sediment up to 10% the size of her body. (no weights of stones were mentioned)
Sediment that is too compacted with what they call fine interstitial sediment- (<0.125mm) will kill the eggs.
So when we dredge.....say it's a 4"....good size right.
We will stir up the fine interstitial sediment- (<0.125mm), collect the heaviest of all sediments and up to 4". So when Mrs. Salmon comes to make a new redd next year she will in fact be able to create a redd much more easily without the fine interstitial sediment- (<0.125mm) and heaviest particles of 4" and under!
These activities of stirring up the finer sediments not only helps the female in creating the redd but will infact insure the stability of the redd through incubation and permit those fry to surface naturally.
Whew!!!!!!!!!
K, I've rambled on for way too long!
CP
Im going to dig out a few links as reference to edit and add to this post later, so keep an eye out.