TITLE:
Power Law Exponents for Vertical Velocity Distributions in Natural Rivers
AUTHORS:
Hae-Eun Lee, Chanjoo Lee, Youg-Jeon Kim, Ji-Sung Kim, Won Kim
KEYWORDS:
Vertical Velocity Distribution; Power Law Exponent; Natural Rivers; Field Measurement; Flow Resistance
JOURNAL NAME:
Engineering,
Vol.5 No.12,
November
26,
2013
ABSTRACT:
While log law is an equation
theoretically derived for near-bed region, in most cases, power law has been researched
by experimental methods. Thus, many consider it as an
empirical equation and fixed power law exponents such as 1/6 and 1/7 are
generally applied. However, exponent of power law is an index representing bed
resistance related with relative roughness and furthermore influences the
shapes of vertical velocity distribution. The purpose of this study is to investigate
characteristics of vertical velocity distribution of the natural rivers by
testing and optimizing previous methods used for determination of power law
exponent with vertical velocity distribution data collected with ADCPs during
the years of 2005 to 2009 from rivers in South Korea. Roughness coefficient
has been calculated from the equation of Limerinos. And using theoretical and
empirical formulae, and representing relationships between bed resistance
and power law exponent, it has been evaluated whether the exponents suggested
by these equations appropriately reproduce vertical velocity distribution of
actual rivers. As a result, it has been confirmed that there is an increasing
trend of power law exponent as bed resistance increases. Therefore, in order to
correctly predict vertical velocity distribution in the natural rivers, it is
necessary to use an exponent that reflects flow conditions at the field.