Lacey’s Regime Theory

Q.

Lacey's scour depth for a stream carrying a discharge of 3 cumecs per meter width having a silt factor 1.2 is_____m

1. 2.64

Q. A channel designed by Lacey's theory has a mean velocity of 1.1 m/s. The silt factor is 1.1. Then hydraulic mean radius will be

1. 1.13 m
2. 2.75m
3. 3.13 m
4. 4.27 m

Q. This discharge carried by a regime canal of width 22 m water depth 2.5 m, is about (in 1.5H : 1V) _______.

1. 84 cumecs
2. 42 cumes
3. 22 cumecs
4. None of these

Q. A channel designed by Lacey's theory has a velocity of 0.88 m/sec. The silt factor is 1.1. then hydraulic mean depth will be

1. 1.95 m
2. 1.76 m
3. 1.63 m
4. 1.50 m

Q. An unlined canal of a trapezoidal shape having side slope 1.5 H : 1 V carries a discharge of Q MLD. The bed material is composed of soil having slit factor f. As per Lacey theory, the velocity of flow is given by $V=\frac{[Q{f}^2{]}^{1/6}}{k}$, the value of k (correct upto two decimal places) is _______.

1. 4.79

Q. For medium silt whose average grain size is 0.16 mm, Lacey's silt factor is likely to be

1. 0.30
2. 0.45
3. 0.70
4. 1.32

Q. An earthen channel has been designed on Lacey formulae to carry a full supply discharge of $30m^3/s.$ The mean velocity of flow at this discharge is:

1. 0.98 m/s
2. 0.76 m/s
3. 2.2 m/s
4. 1.36 m/s

Q. A regime canal carries silt of median size 0.25mm. the Lacey's silt factor of this silt is

1. 0.66
2. 0.88
3. 0.44
4. 0.22

Q. A stable channel is to be designed for a discharge of $Q{m}^{3/}s$ with silt factor f as per Lacey's method. The mean flow velocity (m/s) in the channel is obtained by

1. ${\left[\frac{Q{f}^2}{140}\right]}^{1/6}$
2. ${\left[\frac{Q{f}^2}{140}\right]}^{1/3}$
3. ${\left[\frac{Q^2{f}^2}{140}\right]}^{1/6}$
4. ${0.48\left[\frac{Q}{f}\right]}^{1/3}$

Q. In designing hydraulic structure in alluvial river, the equation that is used to calculate the normal depth of scour R for a discharge intensity of $q{m}^3/s/m$ is :

1. 
   $R=1.35{\left(\frac{q}{f}\right)}^{2/3}$
2. $R=1.2{\left(\frac{q^2}{g}\right)}^{1/3}$
3. $R=1.35{\left(\frac{q^2}{f}\right)}^{1/3}$
4. $R=4.75(q{)}^{1/2}$

Q. For a Lacey channel to carry $5m^3/sec$ through a $0.5mm$ sand, the bed slope will be $1:k$. The value of $k$ is ____

1. 3052

Q. As per Lacey's method for the design of alluvial channels, identify the true statement from the following:

1. Wetted perimeter increase with an increase in design discharge
2. Hydraulic radius increases with an increase in silt factor
3. Wetted perimeter decreases with an increase in design discharge
4. Wetted perimeter increases with an increase in silt factor

Q. In a Lacey regime channel:
1. The bed load is zero
2. The suspended load is zero
3. The bed slope is a function of the full supply discharge and the silt size.
Which of the above statement is/ are correct?

1. 1 and 2
2. 3 only
3. 2 and 3
4. 2 only

Q. A trapezoidal Lacey channel carries $35m^3/sec$ discharge with a sit factor of $0.9$. The side slopes are $1H:2V$. The depth of flow will be ___ m.

1. $3.45m$
2. $2.36m$
3. $1.83m$
4. $6.5m$

Q. A channel designed by Lacey's theory has a mean velocity of 1.28 m/s. The silt factor is unity. The hydraulic mean depth will be ____ m.

1. 4.096

Q. If the flood discharge flowing in a river is $6400m^3/s$, then its wetted perimeter as per Lacey's theory is likely to be

1. 400 m
2. 380 m
3. 360 m
4. 320 m

Q. The Lacey's silt factor for a particular alluvium is 2.0. This alluvium would comprise

1. Medium sand of size 0.5 mm
2. Coarse sand of size 0.75 mm
3. Medium bajri of size 1.3 mm
4. Coarse bajri of size 2.4mm

Q. What will be the regime scour depth for a rectangular channel having 30 m width carrying 430 cumecs water if the average grain size of bed material is 0.14 mm.

1. 2.03 m
2. 5.92 m
3. 7.12 m
4. 9.16 m