FLOOD06972

• County: Statewide
• Basin: Statewide
• Title: Method of Estimate Effects of Flow-Induced Vegetation Changes on Channel Conveyances of Streams in Central Arizona
• Date: 1/1/1998
• Prepared For: Central Arizona
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

SI~D 3a

Vflex values are 8.85 ft-Ib and 63.2 ft-Ib for the
brush and willow, respectively, for all flows
(table 10). Go to STEP 4.

SleD 3b

Vflex values remain constant for all flows. Go to
STEP 4 (Slep 4b).

SleD 3c

Vflex values remain constant for all flows. Go to
STEP 4 (Step 4c),

STEP 4. Determine the orientation of the
vegetation (either oriented randomly or parallel to
flow) as well as the cross-section area of flow
blocked by vegetation, and the ratio of hydraulic
radius to average vegetation height for the selected
discharge. Determine the vegetation-blocking
coefficient, ChlDcking> the vegetation-distribution
coefficient, Cdisl' and the flow-depth coefficient,
Cdeplh (tables 4, 5, and 6).

SleD 4a

ChlDcking is equal to 4.0 for both vegetation
types, Cdisl is equal to 1.0 for both vegetation
types and, for the 2-year flow, Cdeplh is equal to
5 and 60 for the brush and willow, respectively,
Go to STEP 5.

Slen 4b

ChlDcking and Cdisf values remain constant. For
the IO-year flow, however, Cdeplh is equal to 1.0
and 20 for the brush and willow, respectively.
Go to STEP 5 (Step 5b).

SleD 4c

Chlocking and Cdisl values are assumed to remain
constant for willow. For the 50-year flow,
however, Cdeplh is equal to 5.0 for willow. Go to
STEP 5 (Step 5c).

STEP 5. Compute the vegetation-susceptibility
index for the selected discharge using equation 3,

SleD 5a

For the 2-year flow, the vegetation-
susceptibility indices are 177 ft-Ib and
15,200 ft-Ib for the brush and willow,
respectively (table 12). Go to STEP 6.

SleD 5b

For the IO-year flow, the vegetation-
susceptibility indices are 35.4 ft-Ib and
5,060 ft-Ib for the brush and willow,
respectively (table 12). Go to STEP 6
(Step 6b),

SleD 5c

For the 50-year flow, the vegetation-
susceptibility index is 1,260 ft-Ib for willow
(table 12), Go to STEP 6 (Step 6c),

STEP 6. Compute stream power for the selected
discharge using equation I,

St~D 6a

For the 2-year flow, computed stream power is
1.78 ft-lb/s/ft2 (table 12), Go to STEP 7.

Slep 6b

For the I O-year flow, computed stream power is
11.6 ft-Ib/s/ft2 (table 12). Go to STEP 7
(Step 7b).

SleD 6c

For the 50-year flow, computed stream power is
28,0 ft-lb/s/ft2 (table 12). Go to STEP 7
(Step 7c).

STEP 7. Plot the values for the vegetation-
susceptibility index and stream power for each
type of vegetation present in the channel (figure 9).
If the values plot below the vegetation-
susceptibility threshold, repeat steps I through 6
using the next largest discharge. If the values plot
above the threshold, no further steps are required.

Effects of Flow-Induced Vegetation Changes on Channel Conveyances 25