Chapter 11--Rosgen Geomorphic Channel Design

Chapter 11
Step 28 Obtain maximum bankfull riffle depth
(d max ) from ratio of maximum riffle depth divided
by mean bankfull depth from dimensionless ratios
of reference reach data (step 7) (table 11–3).
d
mbkf
d
=
d
⎛ ⎡
⎢
⎝
⎜
⎣⎢
mbkf
⎞
⎠
⎟
bkf ref
⎤
⎥ d
⎦⎥
bkf
Rosgen Geomorphic Channel Design
(eq. 11–18)
Step 29 Determine entrenchment ratio of proposed
channel by measuring the width of the
flood-prone area at an elevation of twice the maximum
bankfull depth (d max bkf ). Entrenchment ratio
is calculated by:
ER Wfpa
= (eq. 11–19)
W
bkf
Step 30 Calculate flood-prone area capacity.
This involves estimating velocity associated with
the cross-sectional area and slope of the stream
channel and flood-prone area. Determine crosssectional
area of the flood-prone area. Plot the
bankfull cross-section and flood-prone area elevation
(2×d max bkf ) and width. Use valley slope for
hydraulic calculations for the flood-prone area.
Estimate roughness from Manning’s equation
based on vegetative cover and other roughness
elements. HEC–2, HEC–RAS, or other models can
be used to obtain the corresponding discharge of
the flood-prone area. Calculate the 50- and 100year
flood levels based on the proposed design.
Use the bankfull channel capacity from step 22.
Step 31 Calculate depth of pool (ratios from
table 11–3):
dmbkfp
dmbkfp
= dbkf
dbkf
ref
⎛ ⎡ ⎞ ⎤
⎢
⎝
⎜
⎠
⎟ ⎥
(eq. 11–20)
⎣⎢
⎦⎥
Step 32 Calculate depth of glide (ratios from
table 11–3):
dg
dg
= dbkf
dbkf
ref
⎛ ⎡ ⎞ ⎤
⎢
⎝
⎜
⎠
⎟ ⎥
⎣⎢
⎦⎥
( ) (eq. 11–21)
Step 33 Calculate depth of run (ratios from table
11–3):
drun
drun
= dbkf
dbkf
ref
⎛ ⎡ ⎞ ⎤
⎢
⎝
⎜
⎠
⎟ ⎥
⎣⎢
⎦⎥
( ) (eq. 11–22)
(210–VI–NEH, August 2007)
Part 654
National Engineering Handbook
Step 34 Calculate slope of pool (ratios from
table 11–3):
Sp
Sp
= S
S ref
⎛ ⎡ ⎞ ⎤
⎢
⎝
⎜
⎠
⎟ ⎥
(eq. 11–23)
⎣⎢
⎦⎥
Step 35 Calculate slope of glide (ratios from
table 11–3):
S
g
Sg
=
S
⎛ ⎡ ⎞
⎢
⎝
⎜
⎠
⎟
⎣⎢
ref
⎤
⎥ S
⎦⎥
(eq. 11–24)
Step 36 Calculate slope of run (ratios from table
11–3):
S
run
Srun
=
S
⎛ ⎡ ⎞
⎢
⎝
⎜
⎠
⎟
⎣
ref
⎤
⎥ S
(eq. 11–25)
⎦
Step 37 Calculate pool-pool spacing (from plan
view and profile layout).
Step 38 Design stabilization/fish habitat enhancement
measures (grade control, energy dissipation,
bank stability, holding cover). See phase
VI.
Step 39 Prepare revegetation plan compatible
with native plants, soil, and site conditions. Make
recommendations on vegetative maintenance and
management for long-term solutions.
Step 40 Design a monitoring plan including
effectiveness, validation, and implementation
monitoring. Prepare maintenance plan to ensure
long-term success.
The variables associated with existing, proposed, gage
station, and reference reach data are summarized
in the form as demonstrated in table 11–14 (Rosgen
1998). The variables used in table 11–14 and forms
used in field data collection are in the Reference
Reach Field Book (Rosgen, Leopold, and Silvey 1998;
Rosgen and Silvey 2005).
11–53