FLOOD05059

• County: Statewide
• Community: Nationwide
• Basin: Statewide
• Title: WSP2 Computer Program
• Date: 5/1/1976
• Prepared By: USDA Soil Conservation Service - Engineering Division
• Floodplain - Doc Type: Educational/Technical/Reference Information

trance loss. If this water surface elevation
does not closely match the headwater ele-
vation (step 2, Road Restriction Analysis),
WSP2 assumes a new discharge and re-
peats this step.
Step 3.-1f open channel flow is impossi-
ble for this headwater elevation, WSP2
assumes full flow. For full flow the water
surface elevation at the culvert entrance
for the assumed discharge is found from a
form of the equation

o = A V 2gh
::.; losses

If this water surface elevation does not
closely match the headwater elevation
(step 2, Road Restriction Analysis), WSP2
assumes a new discharge and repeats this
step.
Step 4.-The headwater elevation is
found assuming iniet control. The water
surface elevation required to pass the as-
sumed discharge through the culvert en-
trance is found from a numerical represen-
tation of the nomographs in exhibits 14-6
through 14-13 of chapter 14 of NEH-4. If
this water surface elevation does not close-
ly match the headwater elevation (step 2,
Road Restriction Analysis), WSP2 assumes
a new discharge and repeats this step.
Step 5.-The discharge that will pass
each culvert opening at the assumed head-
water elevation is the lowest discharge de-
rived from the computations of open chan-
nel flow, full flow, and inlet control.
Step 6.-lf there are identical culverts,
WSP2 multiplies the discharge from step 5
by the number of culverts that are identical.
The lengths important to the culvert anal-
ysis are found in the input as follows:
1. The reach length on the ROAD card is
the distance from the downstream end of
the culvert to the exit section.
2. The third data field of the CULV2 card
gives the cu Ivert length.
3. The reach length on the approach sec-
tion REACH card is the distance from the
approach section to the upstream end of
the cu Iverl.

Contracted opening bridge loss analysis
The WSP2 computer program can ana-
lyze bridge losses by a contracted opening
method based on the following equation:

o = C(CA) V 2gh
1- (~~)'

where C is the coefficient of discharge, CA
is the area within the contracted section,
and AA is the approach section area.
The C value at most bridges ranges from
0.7 to 0.9. If flow turbulence approaching
the bridge opening is relatively low, C value
is about 0.9. If flow turbulence is high, C
value may be as low as 0.4 to 0.5. In deter-
mining C value, consider the following: (1)
shape of abutments (square cornered or
shaped to reduce turbulence); (2) number
and shape of piers; (3) degree of skew; (4)
number and spacing of pile bents (closely
spaced bents increase turbulence); (5)
presence of trees, drift, or other obstruc-
tions at or approaching the bridge; (6)
C value may decrease as discharge in-
creases.

Evaluation of Acres Flooded

For any reach, ir:1formation for three types
of flooded areas can be found. The three
types are damage (D), nondamage (N), and
channel (C) areas. The letter designation
D, N, or C on the segment definition cards
determines in which category a segment
will be placed. The total flooded area for
the reach is the total width fiooded times
the flood-plain length (Field 5 on the reach
card). The total channel area is the sum of
the width of each channel times the channel
length (Field 6 on the reach card). The
nondamage area is the total nondamage
width flooded times the flood-plain length
(Field 5). The damage area is then the total
flooded area minus the nondamage area
and the area in channels.

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