
Hydraulics Engineering  Errata for HEC18, HEC20, and HEC23
(As of September 6, 2001)
HEC18 (Fourth Edition)
p. xii 
Definition of k_{s}:
k_{s} = Grain roughness of the bed, m (ft). Delete: "Normally taken as the D_{84} of the bed material."

pp. 2.8 and 2.9 
Delete last sentence p. 2.8 which continues on p. 2.9 that reads "If the magnitude of the 500year flood is not available from a published source, use a discharge equal to 1.7 times the Q_{100}" and substitute the following:
"For guidance for a particular state in determining the magnitude of the 500year flood, contact with the U.S. Geological Survey Water Resources District office is suggested."

p. 5.15 
Example Problem 3, y_{2} equation:
Add a close parenthesis so denominator reads (0.0003)^{2/3} (91.4)^{2}

p. 6.1 
First paragraph, 3rd line should read:
"...cohesive or noncohesive..."

p. 6.4 
Definition of K_{4}:
Delete ..."and Table 6.4."

p. 6.6 
Last sentence in bold should read:
The minimum value of K_{4} is 0.4.
Delete: "and it should only be used when V_{1} < V_{ic D50}."

p. 6.7 
Equations 6.9 and 6.10:
F should be Fr_{1}

p. 6.13 
Equation 6.14: K_{s} in numerator and denominator should be k_{s}
Definition of k_{s} should read:
k_{s} = Grain roughness of the bed (normally taken as the D_{84} for sand size bed material and 3.5 D_{84} for gravel and coarser bed material, m (ft)

p. 6.23 
Last paragraph, first sentence should read:
"The angle of repose of cohesionless material..."

p. 6.28 
Equation:
"1n" in numerator and denominator should be "ln."
"K_{s}" in denominator should be "k_{s}."

p. A.9 
Appendix A, Table A.7:
For the Kinematic viscosity column, the values should be multiplied by 10^{5} not 10^{4}.

p. E.3 
Appendix E, title should be:
Sturm Abutment Scour Equations

pp. E.4  E.7 
Throughout the Appendix: The subscript "o" should be "0" (zero), i.e. "Y_{fo}" should be "Y_{f0}"
The subscripts "l" and "i" should be "1" (one) i.e., "V_{ml}" should be "V_{m1}" and "V_{mic}" should be "V_{m1c}"

p. E.5 
Second paragraph, 5th line should read:
"the denominator in the above equation..."

p. E.6 
Item 6c: First line should be:
"Compute the critical velocity..."

p. E.7 
Item 8a:
Under "where:" change the "x_{a}" in the equal to less than expression to "X_{a}"
Item 9 should read:
"...scour depth, y_{s}, from Equation E.1."
Item 10, last paragraph, last line should read:
"equation presented in Section E.3."

p. E.8 
Reference #2, second line:
Delete "September" and add "FHWA Report No. FHWARD99156, McLean, VA."

p. F.3 
First paragraph, second line should read:
"The equations and method are presented..."

HEC20 (Third Edition)
p. xi 
Definition of :
= Density of water, kg/m^{3} (slugs/ft^{3})

p. 6.15 
Definition of k_{s} should read:
k_{s} = Grain roughness usually taken as 3.5 D_{84} for gravel and coarser bed material, m (ft)

p. 8.4 
Reference #46 should read: 46. "Leopold, L.B. and ..."

p. A.9 
Appendix A, Table A.7:
For the Kinematic viscosity column, the values should be multiplied by 10^{5} not 10^{4}.

HEC23 (Second Edition)
p. ix 
Definition of :
= Fluid density, kg/m^{3} (slugs/ft^{3})

p. 7.17 
Figure 7.11 Flexible Conduit description should read:
"l" UV RESISTANT RUBBER HOSE"

p. 8.4 
Reference #46 should read...
46. ..."Geosynthetic Design and ..."
The same change should be made to this reference in:
DG1, p. DG1.16
DG3, p. DG3.6
DG4, p. DG4.23
DG6, p. DG6.27
DG7, p. DG7.9
DG12, p. DG12.21

p. DG6.3 
Title of Design Guideline 6 should read:
Concrete Armor Units

p. A.9 
Appendix A, Table A.7:
For the Kinematic viscosity column, the values should be multiplied by 10^{5} not 10^{4}. 

