Results - Response of Flood Events to Land Use and Climate Change - page 146

The recorded and modeled maximum discharge (m 3 /s) in the Ubaye River

Table 6.9

Number Years Maximum hourly discharge Number Years Maximum hourly discharge

1957 a 1 480 17 1995 80.47

2 1980 80 18 1996 54.47

3 1981 87.35 19 1997 89.25

4 1982 61.5 20 1998 83.17

5 1983 101.24 21 1999 92.33

6 1984 88.03 22 2000 129.34

7 1985 76.77 23 2001 119.38

8 1986 86.5 24 2002 84.67

9 1987 59.39 25 2003 70.83

10 1988 30.34 26 2004 42.08

11 1989 42.41 27 2005 89.06

12 1990 34.75 28 2006 50.41

13 1991 81.51 29 2007 18.72

2008 a 14 1992 65.18 30 205

15 1993 86.37 31 2009 89.07

16 1994 182.92

a

The recorded maximum discharge (m 3

/s)

6.7 Roughness Values

The roughness coefficients varied between 0.02 and 0.07 m -1 /3 s-1 according to
characteristics of natural channel. The friction coefficients were adjusted in order
to achieve the best fit between the simulated and observed water stages. These
roughness values are based on land use maps which were digitized according to
related aerial photos (Fig. 6.16 ).
Based on the available aerial photo, six roughness maps were prepared to use as
an important input data in flood modeling. The results of the coefficient values are
presented in Fig. 6.17 . Distribution of roughness coefficients in a channel section
is an important aspect that needs to be addressed properly. A roughness value
underestimates the discharge and a low value can overestimate.
The selection of a suitable value of n is the single most important parameter for
the proper estimation of velocity in an open channel.
For being sure about the correct selected roughness value for the channel, the
model was run for different values of 0.02-0.07. The result of hydraulic depth was
compared with observed data at Abattoir Bridge. Manning's value of 0.02 was