FLOOD06873

• County: Statewide
• Basin: Statewide
• Title: Hydraulic Engineering volume 1
• Date: 1/1/1994
• Prepared By: American Society of Civil Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

,

.

.1

114

HYDRAULIC ENGINEERING '94

Fig. I: Heights of roughness protrusions

The protrusions heights distribution curve has been determined only from the
wetted perimeter of bed. excluding the bank area. Range of the bed material data is
slaled in Tab. 2.
Tab. 2: Rang. of bed m.t.rl.1 d.t.

kso kl6 D!\lJ D84
minIm) 0.0340 0.08 0.066 0.112
maxIm) 0.055 0.122 0.136 0.300

Results of field measurements

Within the evaluation of field data from the Sumava mountain rivers the
parameter a in Ih. Eq. I. was computed using the BA THURSTs (1985) equalion.
For experimental reaches its values varied from 11.27 to 11.96. Therefore its
influence on the profile resistance changes is possible to be considered to be small,
and that is why to be considered constant, too. In spite of it, the parameter 1ft was nol
constant but varied in dependency on friction slope Sr (Fig.2).

18 ___~____ .___._____n_." .-.
___n___. __ __..__._ ~..
16 .-.. -.. -- ---.-..---- ...--.--..
--'- .~-- ------~
14 -..--.----- -- --- ----.

I;;
,
~
'"
.
0!-
R

. 12 ==---=..~~- _=~JID =-~.

10. --.----'
9
8
1

6 lli.ii;-

5----
0..0.0.2 0.0.0.3

0.001 0.U09 0.011

0.004 0.005
S rl'l

Fig. 2 Variation of the parana efer m with the average friction slope Sr in
river ....h.. (k, ~ ~ Sr- S)
The changes of the parameter m were the most expressive in those reaches
where longitudinal non-unifonn decelerated flow occurred (S < Sr). In the range of
river sites this character of flow was caused by the down stream expansion of the
cross section, which means by decreasing the velocity heads. On the contrary. in

.

EVALUATING H.uW RESISTANCE

115

those sites with longitudinal non-uniform accelerated now (S > Sr). the measured
values of m changed relatively little. The measure of non-uniformity of the now was
expressed by means of the parameter 0 = I - S/Sr. From IIIJd data the result equation
for parameter In (for ks == k,50) was derived in the form

( )11- 2.136)
m; 159.1 SrO.!\lJl (4)

By this way the tffect of longitudinal slope and considering Ii also the eITect of
non-uniform deceler-ated now was included. For the region of accelerated now (S >
Sr) the hypothesis was expressed that its effect on now resistances can be neglected
and the parameter m for these cases can be estimated in the same way as for those
ones in the region of uniform now. However, it would be more applicable to verify
this presumption for more empirical data.
Using the same procedure for ks = kl6 a similar equation has been derived:

( )(1- 3.375)
m; 96.9S~.S64 (5)

The same procedure has been used also for hydraulic roughness being expressed
using grains Dj from Ihe grain size dislribulion curve (MARESOV A. MARES.
1991).

Using these values of parameter 1ft for calculation of UIU.. these theoretical
values, compared with measured values of UIU. are showing the following algebraic
mean of the percentage differences E. and the standard deviation of the percentage
diff.r.nces .. (Tab.3)
Tab..3 Evaluating the result equations

kso kl6 D!\lJ D..
& -0.4% -0.9% -1.4% -1.0"10
. 12.2% 11.9% 9.411/0 13.10/.

0.1

. rA
~~..

.

S 0.01 ---

f ~ 0.08 --~. .
f~O.07
7.10,06
0.05 -..

Fig. J:

O.fJ4 . - -------~-
0.1 OJ R Iml D.S 0.1

Dependency of Manning roughness coeffICient n on hydraulic radius

-