Unusual Request - Roughness Calibration

Hello Russel,

thanks for your response and the reference.
I fully agree that this is an very old issue and that
measurements/studies have been carried out exactly on this topic (btw.
you can access the report you have quoted online under :
http://www.engr.utk.edu/hydraulics/openchannels/Index.html).

I just wonder, how many of us really take the values straight from any
kind of resource and have immediately the best fitting parameter set
without having to calibrate? My small experience tells me it happens
very, very rarely and then very often to very experienced users.
Therefore, I am interested in your personal, practical experience.

Florian Pappenberger
f.pappenberger@lancaster.ac.uk

Hello;

There's a Special Issue of 'Journal of Hydrology' (Elsevier Science
Publishers B.V.) entitled "Analysis of Extraordinary Flood Events" -
volume 96 (1987), which is a compendium of quality materials related to
the large floods' hydrology & hydraulics. The generous contributions
from the USGS fellows, UK Wallingford hydrology/hydraulics research,
USCOE, USBR, and of course from the Chinese practitioners &
academicians has rendered the document an invaluable reference.
Relevant works to this thread are, amongst others, the papers by James
Cook ,by Robert Jarrett and by W.H.Kirby,all from the USGS. Reference
to the earlier/supporting works are found there.

Another approach would be to preliminarily refrain from estimating the
Manning's N altogether, using some generalized regression equations to
estimate the flow. This has been followed by Rigg in the 70's I think,
and extended/augmented by Dingman & Sharma in the late 90's, but for the
'bankfull' flow only (~1.5- to 7-Year flood,perhaps):

Dingman,S.L.,& K.P. Sharma,1997: " Statistical Development & Validation
of Discharge Equations for Natural Channels", Journal of Hydrology,Vol.
199 (No.1-2),pp 13-35.

Floodflow hydrology & hydraulics is a highly controversial subject with
many dark sides yet to be lime-lighted out,for the practitioners I
believe. It's great that such questions are posed here, which raises
the hope of getting some useful/promising leads then.

Mostafa Bozorg-Zadeh
Independent Consulting Engineer

> Forgive me if this is old news, but the USGS Water Supply Paper 1849 -
Roughness Characteristics of Natural Channels is a study of this very
issue. The USGS sloved Manning's Equation for n on a number of guaged
streams. Many of them they solved for n for multiple events to show how
roughness was affected by Q.

> The book was frist printed in 1967, but is an excellent reference. It
is full of color pictures so that you can see the bank/stream
characteristics, and provides tablized data and channel cross sections
for each stream studied. The book is still available through the USGS
Denver office (303)202-4700.

> Hope this helped some.
> Russell C. Reed
> rreed@HELENANET.COM

For those who are interested, the formal reference is:

Irrigation Systems for the 21st Century, Proceedings of a Conference
sponsored by the Irrigation and Drinage Division of the American Society
of Civil Engineers and the Oregon Section, ASCE, July 28-30, 1987.

It's published by ASCE - I looked it up on the ASCE website &, as it
happens, it's available but being cleared out, & is being offered at
$9.00 for U.S. sales, $10.80 for international sales, marked down from
$72.00. You can find it at:

http://www.pubs.asce.org/BOOKdisplay.cgi?8703953

Cheers,
Thomas H. Walker, P.G.
twalker@ffeng.com

As a side issue regarding the variability of roughness coefficients, the
Hydrologic Engineering Center did a study regarding the variance in
roughness coefficient estimates with Corps of Engineers employees taking
training courses at HEC in the mid-1980's. The compared the variation
in roughness coefficients estimated by inexperienced engineers taking
the introductory HEC-2 class to the roughness coefficients estimated by
the more experienced engineers taking the advanced HEC-2 and unsteady
flow classes. They provided the students with a USGS publication showing
roughness coefficients for various channels. They showed slides of
various streams studied by HEC around the country. They found that the
variation in roughness coefficient estimates was greater for the more
experienced engineers. They attributed this to the more experienced
engineers relying less on the USGS publication and using their
experience in modeling streams to estimate the roughness coefficient. I
am not aware of a publication documenting the results of the study.

John G. Morgan
john.morgan@cte-eng.com