3. Sédiment Transport
51
The shape of the waves influences the cross shore sédiment transport. In
shallow water, waves are mostly in asymmetrical form with crest velocity
is more which are directed towards onshore and trough velocity is lower,
directed towards offshore. These flows results in suspended sédiments to
move shoreward and bed load sédiments seaward. As waves propagate form
offshore to shallow water it deforms, in addition it expériences transformation due to its breaking and thereafter, the dissipation of energy takes
place rapidly, i.e., the wave enters the wave decay région. The région inshore
of the breaker point is divided into a breaker transition and broken wave
régions. Based on wave propagation, Larson and Kraus [1989] divided the
shallow région of coast into four zones as shown in Fig. 3.9 showing different hydrodynamic properties and contribute to different influence and
relationships for sédiment transport.
The pre-breaking zone (I) is from the depth seaward of significant sédiment transport to the breaker point. The breaker transition Zone (II) is
from the breaker point to the point where waves plunges or curls. The zone
of broken wave (III) is from the wave plunging point to the area of offshore end of the surf zone and the swash Zone (IV) is from the shoreward
boundary of the surf zone to the shoreward lirait of the run up.
The knowledge of both cross shore and along shore sédiment transport
is essential foundation for numerical modelling. Estimation of cross shore
transport rates may be done through empirical relationships which for the
different zones are,
Zone 1:
q = ç6exp{-Ai(z -£&)}
(3.15)
Zone 2:
q = gpexp{—A2(z - æp)}
(3.16)
q — net cross-shore transport rate (m3/m/sec)
Ai,2 — spatial decay coefficients in transport Zones 1 and 2, (m-1)
X — cross-shore co-ordinate from the seaward end of the beach profile
The subscripts b and p in Eqs. (3.15) and (3.16) dénoté quantities evaluated at the breaking point and the plunging point, respectively. Spatial decay
coefficients Ai and A2 are estimated empirically [Larson and Kraus, 1989] in
the sédiment transport rate in the same above équations are given by,
Ai = 0.4(T5oM)°'47
(3-17)
A2 = 0.2Ai
(3.18)
51
The shape of the waves influences the cross shore sédiment transport. In
shallow water, waves are mostly in asymmetrical form with crest velocity
is more which are directed towards onshore and trough velocity is lower,
directed towards offshore. These flows results in suspended sédiments to
move shoreward and bed load sédiments seaward. As waves propagate form
offshore to shallow water it deforms, in addition it expériences transformation due to its breaking and thereafter, the dissipation of energy takes
place rapidly, i.e., the wave enters the wave decay région. The région inshore
of the breaker point is divided into a breaker transition and broken wave
régions. Based on wave propagation, Larson and Kraus [1989] divided the
shallow région of coast into four zones as shown in Fig. 3.9 showing different hydrodynamic properties and contribute to different influence and
relationships for sédiment transport.
The pre-breaking zone (I) is from the depth seaward of significant sédiment transport to the breaker point. The breaker transition Zone (II) is
from the breaker point to the point where waves plunges or curls. The zone
of broken wave (III) is from the wave plunging point to the area of offshore end of the surf zone and the swash Zone (IV) is from the shoreward
boundary of the surf zone to the shoreward lirait of the run up.
The knowledge of both cross shore and along shore sédiment transport
is essential foundation for numerical modelling. Estimation of cross shore
transport rates may be done through empirical relationships which for the
different zones are,
Zone 1:
q = ç6exp{-Ai(z -£&)}
(3.15)
Zone 2:
q = gpexp{—A2(z - æp)}
(3.16)
q — net cross-shore transport rate (m3/m/sec)
Ai,2 — spatial decay coefficients in transport Zones 1 and 2, (m-1)
X — cross-shore co-ordinate from the seaward end of the beach profile
The subscripts b and p in Eqs. (3.15) and (3.16) dénoté quantities evaluated at the breaking point and the plunging point, respectively. Spatial decay
coefficients Ai and A2 are estimated empirically [Larson and Kraus, 1989] in
the sédiment transport rate in the same above équations are given by,
Ai = 0.4(T5oM)°'47
(3-17)
A2 = 0.2Ai
(3.18)