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