STUDY OF THE ROUGHNESS CHARACTERISTICS OF

PLANT SPECIES IN

CALIFORNIA RIVERS

By

U.C.Davis J.Amorocho Hydraulics Laboratory

The objectives of this study:

1. to determine the hydraulic roughness (Manning’s n) associated with each of California native plant species under various flow conditions (from low to high flows),

2. to compare these roughness values to bare soil roughness conditions that may be present on the floodplains in river reaches where these plants occur,

3. to quantify the response of stems of known density, diameter and height of various native plant species under different flow conditions;

Flume Setup for Roughness Study

H

Depth Control Weir

x =49'

31'

x =60'

V

2’

Flume tail tank

x =0'

x =66'

Pumps

x =17'

17' 32'

6’

80'9'

Head

Tank

Bare Soil Sample Layout

4 ft bin Width

Flume width 5 ft

8 ft

6 ft

2 ft

Flume Body Cross-section

Partial Plan View

8 bins with a total distance of 32 ft

bin length 4 ft

4 ft

STREAMBED BARE SOIL SAMPLE

PREPARATION

Measurement Instrument

1) SonTek ADV 3-D Velocimeter

Velocity profiles at various locations

2) Point Gages with Stilling Tube

Hydraulic head

3) Ultrasound Flow Meter:

Total Discharge

4) Digital Floater

Water surface wave

Hydraulic Measurements

For each individual experimental setup for a plant species, three different depths (three different hydraulic radii)

are taken, where depths depend upon the species being studied.

For each depth, three different cross-sectional average velocities are considered

(within the range of 0.5 – 5 ft/second).

Therefore, for each experimental setup, nine different depth – velocity combinations are considered.

Each experimental setup for a particular plant species is repeated three times, with new plant patches each time,

to obtain three independent replicates.

Velocity measurement locations in a cross-section

4 ft bin Width

Flume width 5 ft

8 ft

6 ft

2 ft

4 ft bin Width

Flume width 5 ft

8 ft

6 ft

2 ft

Water depth higher than 2 ft

Water depth lower than 2 ft

The velocity head profile is determined from the cross-sectionally-averaged velocity measurements at three specified locations in the plant patch section.

Hydraulic radius is directly measured (depth and width of flow) through the plant patch section.

The friction slope is determined from the measured total energy head (hydraulic head plus velocity head) gradient under each average depth – average velocity combination.

The hydraulic head gradient is determined from measuring three cross-sectionally-averaged water depths (water surface elevations) along the longitudinal direction of the flume within the plant patch section.

A Manning’s roughness coefficient that corresponds to the specified plant species and specified average hydraulic radius – average velocity condition is calculated.

PRELIMINARY EXPERIMENTAL RESULTS

BASED UPON

FIRST BARE SOIL REPLICATE

WHILE

STANDARDIZING THE EXPERIMENTAL PROCEDURES

Water Surface and Energy Gradient LineS61 (H=1 ft, V=1 ft/s)

1

1.005

1.01

1.015

1.02

15 20 25 30 35 40 45 50

x(ft)

ft

E= (H + hv)

H(Point Gage)

Water Surface and Energy Gradient LineS71(H=1 ft, V=2 ft/s)

0.98

1

1.02

1.04

1.06

1.08

15 20 25 30 35 40 45 50x(ft)

ft

E= (H + hv)

H(Point Gage)

Water Surface and Energy Gradient LineS51(H=2.5ft, V=5 ft/s)

2.50

2.60

2.70

2.80

2.90

3.00

15 20 25 30 35 40 45 50

x(ft)

ft

E= (H + hv)

H (Point Gage)

Water Surface and Energy Gradient LineS21 (H=5ft,V=2ft/s)

5.155.165.175.185.195.205.215.225.23

15 20 25 30 35 40 45 50

x(ft)

ft

E= (H + hv)

H (Point Gage)

Water Surface and Energy Gradient LineS41(H=2.5,V=2ft/s)

2.542.552.562.572.582.592.6

2.612.62

15 20 25 30 35 40 45 50

x(ft)

ft

E= (H + hv)

H(Point Gage)

Measured Water Surface and Energy Gradient Lines

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0.0240

0.0260

0.0280

0 100,000 200,000 300,000 400,000 500,000

Reynolds Number

Ma

nn

ing

's R

ou

gh

ne

ss

Co

eff

icie

nt

y = 0.0199x + 0.0121

R2 = 0.8703

0.0100

0.0120

0.0140

0.0160

0.0180

0.0200

0.0220

0.0240

0.0260

0.0280

0.000 0.200 0.400 0.600 0.800

Froude Number

Ma

nn

ing

's R

ou

gh

ne

ss

Co

eff

icie

nt