2012-08-01_HYDROLOGY - M2011028

• Permit No: M2011028
• IBM Index Class Name: HYDROLOGY
• Doc Date: 8/1/2012
• Doc Name: RIP RAP CHANNEL DESIGN COMMENTS
• From: DRMS
• To: RUSSELL ENGINEERING
• Email Name: TC1
• Media Type: D
• Archive: No

/L1- 201(-- 02 S
Cazier, Tim
From: Cazier, Tim Cr%kl"O
Sent: Wednesday, August 01, 2012 10:51 AM
To: 'Steve Winters TasrE�{
Cc: Pickford, Kate
Subject: RE: Animas Glacier Gravel Pit - riprap channel design comments
Attachments: M- 11- 28_BasinRiprap v4.pdf; M- 11- 28_RiprapCheck.pdf
Steve,
I've gone through your calcs and checked what I could (I could not check Cv, as I don't know the channel bend radius).
You appear to be on the right track, but there are some assumptions that need to be adjusted or revised:
1) 1 strongly recommend not using rounded riprap. Angular riprap is much more stable due to better interlocking.
2) Your flow depth & velocity appear to be based on a Manning's n of 0.02. This is too low for riprap. Riprap
channel designs need to be evaluated for both stability (i.e., velocity) and capacity. A range of Manning's n
between 0.035 and 0.040 is typically sufficient and good engineering practice. Flow depth is an important
parameter from a shear stress perspective.
3) Your selection of the variable Vss implies you intend to armor only the side slopes. The bottom of the channels
need to be armored as well.
4) Your K1 value uses an angle of repose of 40 degrees. I suspect that is not valid for rounded riprap, but I don't
have any definitive information there. Again, I strongly recommend angular riprap.
I've attached my comments for the first page and a summary calculation sheet with my results. Those may vary from
what you end up with depending on channel bend radius, angle of repose for the riprap and the velocity distribution
coefficient.
I am still reviewing the drainage report.
Please let me know if you have any questions. I'll be out of the office Thursday afternoon and Friday this week.
Tim Cazier, P.E.
Environmental Protection Specialist
Colorado Division of Reclamation, Mining and Safety
1313 Sherman Street, Room 215
Denver, CO 80203
ph: 303- 866 -3567 x8169
fax: [phone]
[e-mail]
From: Steve Winters [mailto:[e-mail]]
Sent: Tuesday, July 31, 2012 11:16 AM
To: Cazier, Tim
Subject: RE: Animas Glacier Gravel Pit
Hey Tim,
Can you take a look at the rip rap calculations prior to me including them within the Drainage Study? I haven't used this
method before, and want to make sure that I'm not missing anything in the calculations or assumptions. Based on the
different flow rates and longitudinal slopes, I ran a few scenarios for the channels so we didn't end up significantly
oversizing large sections of the riprap. Also, since the undisturbed channel requirements are so small, we'll likely just go
with a D50 of 6" to keep it simple.