KANSAS RIVER KAW INTAKE SEDIMENTATION STUDY

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Kansas River KAW Intake Sedimentation Study

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July 11, 2012


KANSAS RIVER
KAW
INTAKE SEDIMENTATION

STUDY


O
VERVIEW

Sediment d
eposition

at the
Kaw River
Water Intake on the Kansas River near Lawrence, KS has created
operational issue
s.
Sand deposits in the vicinity of the intake have led to sediment entering and settling
in the intake structure, as well as sediment entering
NHC
,
working as a sub
-
consultant
, is assisting
Black
and Veatch to assess the reasons for the

deposition

and possibl
e alternatives to reduce sediment in the
Intake.

The sedimentation analysis
includes an initial review of the
USGS sediment and flow discharge records
.
After the 2D hydrodynamic modeling is completed a qualitative assessment of the scour and erosion
prope
nsity in the reach
was

done.


T
he
Army Corps of Engineers AdH depth averaged 2
Dimensional M
odel was used for the hydraulic
modeling tasks. The
2D hydrodynamic model was developed using the provided bathymetry and
proposed Bowersock Dam operations. An exi
sting conditions model was developed and calibrated from
this data. The Existing Conditions model was run

for 6 discharges between 7,911
cfs
-
232,500cfs to assess
mobility.

From these results qualitative assessments were made to evaluate scour and erosion
propensity in the reach. This lead to outlining possible alternatives including retrofitting or moving the
current intake as well as rehabilitation of old intakes.

The two alternative models that included the addition of dikes in the channel were modeled
using
AdH
.
Additionally two comparison analyses were done to answer questions
about previous hydraulic
conditions
that came up during the study. The first compared velocities near the intake for the old and
new Bowersock Dam Gate Elevations. The second ana
lysis tried to recreate the pre I
-
70 Bridge
Renovation

Geometry to

compare velocities
in that region with
the current bathymetry. These were all
done using the 90%
Exceedance

Flow. This discharge was chosen since
it represents a mobile bed
condition and is

a
more common
occurrence
than the
other
modeled
events.



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K
ANSAS
R
IVER
S
EDIMENT
D
ATA

The U.S. Geological Survey (USGS) collected bed material and suspended sediment data at the Lawrence
gage (#06891080) and Lecompton gage (#06891000). Most of the sediment

data were collected in the
1970s and 1980s. A few suspended sediment measurements were conducted in the early 2000s. The
measured sediment data are available from the USGS website at http://waterdata.usgs.gov/nwis. Below
is a brief discussion of th
e publi
shed USGS sediment data.

Bed Material

The USGS collected a large number of bed material samples at the Lecompton gage (during 1975
-
1989)
and a few samples at the Lawrence gage (in 1977 and 1989). The measured bed material gradations are
shown in Figure
s

1

and 2
. Average grain size distributions calculated from the USGS data are shown in
Figure
3
. According to the USGS measurements, bed material in the study reach of the Kansas River
mostly consist of medium to coarse sand and gravel. Medians size of the bed

material samples ranges
from about 0.13 mm to 1.1 mm at the Lawrence gage and from about 0.25 mm to 3 mm at the
Lecompton gage. The average median size of the bed material is about 0.35 mm for the Lawrence gage
and 0.6 mm for the Lecompton gage. The maxim
um grain size in the USGS bed material samples is 16
mm at Lawrence and 32 mm at Lecompton. Typical bed material deposits in the study reach are shown
on the photo
graphs in Figures 4 and 5 show.

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Figure
1
:
Grain size distribution f
or bed material in Kansas River at Lawrence (USGS data).


Figure
2
:
Grain size distribution for bed material in Kansas River at Lecompton (USGS data).


0
10
20
30
40
50
60
70
80
90
100
0.001
0.01
0.1
1
10
100
Percent finer
Bed material grain size (mm)
USGS gage 06891080 Kansas River at Lawrence
6/22/1977
6/24/1977
6/24/1977
4/12/1989
Average 1977
-
1989
0
10
20
30
40
50
60
70
80
90
100
0.001
0.01
0.1
1
10
100
Percent finer
Bed material grain size (mm)
USGS gage 06891000 Kansas River at Lecompton
10/17/1975
3/11/1976
5/23/1977
6/13/1978
7/17/1980
9/28/1981
Average 1975
-
1989
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Figure
3
:
Average grain size distribution for bed
material in Kansas River at Lawrence and Lecompton (USGS
data).


Figure
4
:
Bed material in Ka
nsas River at Highway 70 Bridge




0
10
20
30
40
50
60
70
80
90
100
0.001
0.01
0.1
1
10
100
Percent finer
Bed material grain size (mm)
Kansas River
Lawrence average 1977
-
1989
Lecompton average 1975
-
1989
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Figure
5
: Sand bar upstream of water intake (View Upstream)



Suspended
Sediment

Suspended sediment is the portion of the total sediment load of rivers that is carried in the water
column.

The USGS publishes the total suspended sediment load which is comprised of wash load and
suspended bed material load. Wash load (clay and s
ilt particles finer than 0.062 mm) is derived from
sources other than the bed, is continuously transported in suspension by turbulent currents, and is not
found in appreciable quantities in the bed. Suspended bed material load is the sediment in suspension

that is comprised of particles (sand and coarser sediment) that are found in appreciable quantities in the
channel bed. With respect to channel morphology, the bed material load is more important component
of the total load because it is derived from eros
ion of the channel bed, because bed material load
particles are constantly being exchanged with bed material, and because it returns to the bed at the end
of a transport event. Suspended bed material load can be calculated from the total suspended sediment

load using grain size distribution data of the suspended sediment (if available).


According to the published USGS data, suspended sediments in the study reach of the Kansas River are
mostly composed of silt and clay, with smaller amounts of fine to coar
se sand. The proportion of wash
load (silt and clay) in the measured total suspended sediment load in the study reach is typically greater
than 70
-
90% for low flows and generally reduces to around 40
-
70% or less for higher flows. The
percentage of silt an
d clay in the USGS suspended sediment samples collected at the Lawrence and
Lecompton gages are shown in Figure
6
.


Total suspended sediment concentrations (SSCs) measured by the USGS are plotted versus flow in Figure
7
. The measured SSC data show signific
ant scatter, which is typical of natural streams and is due to
seasonally variable delivery of sediment into the stream system from the watershed as well as
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measurement errors. According to the USGS measurements, SSC in the study reach of the Kansas River
range from less than 100 mg/L at low flows to 1,000
-
7,000 mg/L at medium and high flows.


Suspended sand loads (bed material loads) calculated from the USGS data are shown in Figure
8
. The
suspended sand data show less scatter compared to the SSCs because

transport of sand is mostly
governed by flow hydraulics rather than supply from the watershed. The measured suspended sand load
in the study reach of the Kansas River ranges from less than 100 tons/day at low flows to over
100,000
tons/day at high flows.

Bed Load

Bed load is the part of bed material load that is moved by the flowing water along the bottom of
waterway and creates bed forms such as dunes and bars. No bed load measurements have been
conducted by the USGS in the study reach of the Kansas River
. Bed load in sand
-
bed rivers similar to the
Kansas River typically constitutes less than 10% of the total sediment load.


Figure
6
:
Percentage of silt and clay in suspended sediment for Kansas River at Lawrence and Lecompton (USGS

data).



0
10
20
30
40
50
60
70
80
90
100
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
Percentage of silt and clay in suspended sediment
Flow (cfs)
Kansas River
at Lawrence 1977
-
1981
at Lecompton 1975
-
1986
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Figure
7
:
Suspended sediment concentration versus flow for Kansas River at Lawrence and Lecompton (USGS
data).



1
10
100
1,000
10,000
100
1,000
10,000
100,000
Suspended sediment concentration (mg/L)
Flow (cfs)
Kansas River
at Lawrence 1977
-
1989, 2002
at Lecompton 1975
-
1989, 2001
-
2002
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Figure
8
:
Suspended sand load versus flow for Kansas River at Lawrence and
Lecompton (USGS data).





0.1
1.0
10.0
100.0
1,000.0
10,000.0
100,000.0
1,000,000.0
100
1,000
10,000
100,000
1,000,000
Suspended sand load (tons/day)
Flow (cfs)
Kansas River
at Lawrence 1977
-
1981
at Lecompton 1975
-
1986
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K
ANSAS
R
IVER
I
NTAKE
AT
L
AWRENCE
2
-
D
IMENSIONAL
ADH

M
ODEL

An Adaptive Hydraulics Model (ADH)

of the reach
was developed to
simulate

the conditions on the
Kansas River near the
Kaw Water Treatment Plant Intake.
Model geometries
wer
e created using the
existing river geometry (provided by Black and Veatch) and for 2 Alternatives developed to reduce
sedimentation near the intake.
The model extended from Bowersock Dam at the downstream boundary
to approximately 1000 feet upstream of the

I
-
70 Bridge. AdH is a US Army Corps of Engineers (USACE)
software designed to solve 2D shallow water problems. This model was chosen for its ability to model
supercritical boundary conditions,
hard structures,
hydraulic jumps and surface waves.

M
ODEL
G
EOMETRY

The base bathymetry and topography was provided by Black & Veatch.
The three existing intakes were
modeled with extents based on provided drawings and aerial imagery. The intake structure top
elevations were set at 813.5 ft for all three structures
.

The plan sheets showed slight variations in
elevations
1
, 2

~0.2 feet it was confirmed with B&V to model them at 813.5 feet.
This

elevation
happens
to correspond

with the downstream control elevation at Bowersock

Dam for FERC activities. The existing
intakes, shown in Figure 9 below, could be a potential hazard for boats in the area if not properly
marked
. The change in Bowersock Dam Elevation from 812 ft to 813.5 ft
will submerge the intakes

for
most flows
.
Nodes

were placed in a higher density around and on the intake structures to define their
shape and the steep change in elevation.
Figure
10
, shows the nodal density around the existing intakes
with the AdH results as a background on the right, and the location

of the intakes and nodes against an
aerial image to the left.


Figure
9
: Existing Intakes







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Figure
10
: Existing Intakes Mesh Data



The I
-
70 Bridge Piers dimensions and locations were mo
deled based on the KTA Bridge Construction
layout
3
. Each set of bridge piers were then modeled as one continuous structure and removed from the
computational domain.
Node density was increased in this region
to better delineate the structure
limits.
An ima
ge of the I
-
70 Bridge Piers taken during the field visit is given below in Figure
11
. Figure
12

shows the nodal density around the piers with the AdH results as the background on the left and the
location of the piers against an aerial image on the right.


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Figure
11
: 1
-
70 Bridge Piers


Figure
12
: I
-
70 Bridge Model Mesh



Detailed plans were not available for t
he 2
nd

Street Bridge
Piers. The Bridge pier dimensions were taken
off of aerial images. The piers were excluded from the computational mesh. Figure
13

shows the nodal
density around the piers with the AdH results in the background to the right and with an aerial image on
the l
eft.


Figure
13
: 2
nd

Street Bridge Pier Mesh




Figure
14
, given below, shows the bed elevation
from the provided,

bathymetry near the intakes. The
current intake is the structure furthest to the left (
West,
Right Bank looking DS). The Bed Elevations near
this intake are in the range of 802.5
-
804 ft. The middle intake has bed elevations between 800
-
802 feet.
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The old intake that is furthest into the river

(east)

has bed elevations
in the range of
798
-
80
0 ft.
T
he
client provided data with Intake readings from July 6, 2012 at the corners of the currently functioning
intake (far left in Figure 14). The elevations from that survey ranged from 801.5
-
803.5 which is within +/
-

1 foot of the elevation range given in th
e bathymetric survey. Changes of 1 foot or more are very
common in a sand bed river so this data agrees well.


The water intake screen spans
elevations
between
806 and 808.6ft

for the existing intake structure
2
. The
minimum difference in elevation between

the
existing
river bathymetry and the existing intake elevation
is 2 feet. Changes in bed elevation due to transient bedforms can be
over
3

feet
.


Figure
14
: Bed Elevation near Intake Structures


H
YDROLOGY

The hydrology is based

on a combination of 2009 FIS Data and USGS Flow Records at Lecompton, both
provided by Black
& Veatch
. The FIS data from 2009 at Bowersock Dam provided by B
lack &
V
eatch

was
for extreme high flow events, given below in Table 1.


Table
1
: High Flow Discharge and Water Surface Elevations


Flow Event

Discharge, cfs

WS Elevation, ft

10
-
yr Peak

89,500

818.9

50
-
yr Peak

179,500

825.3

100
-
yr Peak

232,500

829.7

500
-
yr Peak

428,000

839.5


This data was used in conjunction with a developed HEC
-
RAS model for the Bowersock Dam Reach

to
develop the downstream boundary elevations
. This HEC
-
RAS model was used to develop a downstream
rating curve of water surface elevation vs. discharge for flows
of interest


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The foundation of the current Bowersock Dam (808 ft) was modeled in HEC
-
RAS as an in
-
stream
structure. The 90% exceedance flow fell into the flow range where the dam elevation was controlled by
the rubber dam. The DS extent for this simulation

was set at 813.5 feet to match the normal pond
elevation.

This information was taken from the 2011 Bowersock Flashboard Replacement Proposal
4
.


The 2
-
yr, 5
-
yr and 10
-
yr
return interval
flows were above the normal rubber dam operating range. For
these fl
ows the rubber dam would be deflated and the gates would be lowered. Th
e

dam geometry was
represented by an inline structure 573.5 feet long, 20 foot wide dam with and elevation of 808 feet.
These dimensions were taken from the Bowersock Rubber Dam option
report
4
. The dam was calibrated
by adjusting the inline structure weir coefficient (2.8) in the HEC
-
RAS model to match the given 10
-
yr FIS
Peak (Table 1). The 10yr peak was chosen since it would most closely simulate the lower flows needed
for the AdH mode
l. The HEC
-
RAS model was able to re
-
produce the FIS Elevation given by the client
within 0.2 feet. Using this HEC
-
RAS model the Water Surface Elevations at the dam were developed for
the 2yr

and 5yr

events. These Water Surface Elevations are given below in

Table 2. The 10
-
year peak
flow given by the client (Table 2) did not match the 10 year FIS discharge also given by the client (Table
1). The 10
-
year peak from Table 2 was used for the modeling (per instruction).


Table
2
: Boundar
y Conditions Generated from the HEC
-
RAS Model Results

Flow Event

Discharge, cfs

WS Elevation, ft

90% Exceed

18,500

813.5, gate controlled

2
-
yr Peak

54,951

816.11

5
-
yr Peak

87,067

818.53

10
-
yr Peak

107,881

819.88


M
ODELED
F
LOOD
E
VENTS AND
B
OUNDARY
C
ONDITIONS

The upstream boundary was set ~1000 feet upstream of the I
-
70 Bridge as a constant discharge. The
downstream boundary was set just upstream of Bowersock Dam. The effects of Bowersock

Dam were
modeled through the downstream elevation rating curve.
Initially 5 flood events were modeled for the
2012
reach

conditions
: the 90%
Exceedance
, the 2
-
yr, 5
-
yr, 10
-
Year and 100
-
Year Return Period Events.
After examination of the results a 6
th

floo
d event was added the 50 %
Exceedance

flow. The 50%
Exceedance

flow discharge is in the range of discharges that are controlled by dam operation so the
elevation was set for this scenario as 813.5 feet. The 50%
Exceedance

flow was modeled after it was
foun
d that sand was mobile for all of the initial 5 flood events. The modeled discharges and downstream
boundaries are given below in Table 3.


Table 3:
AdH Flow Scenarios

Flow Event

Upstream Boundary
Discharge, cfs

Downstream Boundary

W
ater
S
urface

Elevation, ft

50% Exceed

7,911

813.5, gate controlled

90% Exceed

18,500

813.5, gate controlled

2
-
yr Peak

54,951

816.11

5
-
yr Peak

87,067

818.53

10
-
yr Peak

107,881

819.88

100
-
Yr Peak

232,500

829.7

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M
ODEL
C
ALIBRATION

The model was calibrated by comparing the AdH 1
00
-
Yr

Model WSE slope to the
FEMA
FIRM
5

for the
same
r
each.
The FEMA FIRM for Douglas County was
obtained

online for this

reach. The
FIRM was for
the 100 year event and included

base flood elevations and
flood
extents
. The FIRM however did not
include the discharge used for the 100 year event.

From the Firm the Base Flood Elevation at the Dam is
given as 827 feet. This is not consistent with the 829.7 feet that the client provided. Without knowing
any fur
ther information on the FIRM the only comparison that can be made is water surface elevation
change. The FIRM showed between 5 and 6 feet of water surface elevation drop for the model extents.
This is consistent with the 5.5 feet of WSE change
computed by
the AdH modl, indicating equivalent
hydraulic roughness in both the F
that the model gave.

E
XISTING
C
ONDITIONS
M
ODEL

The Existing Conditions Model results are given
within this section

for the six design discharges.

Velocity
and Depth plots are given for t
he modeled extent, near the intakes, and for the extent of the proposed
project conditions for each discharge event.
The Manning’s roughness for all of the runs was set at 0.03.
The velocities shown on the top of the intake structure are artificially high
for the 50% and 90%
Exceed
a
nce Flows. There are modeling limitations for very low depth mid
-
channel points using a depth
-
averaged model.


Median grain size and depths near the intakes were used to compute critical flow velocity ranges for
sediment movemen
t. The depths
near the intakes were extracted from the AdH results.
The median
grain size was computed from the average of 4 bed material samples collected by the USGS at Lawrence
in 1977 and 1989. Velocity data was extracted from the River2D results for c
omparison to the critical
flow velocities to determine if sediment movement is expected in the area.


Table
3
: Computed flow velocity and depth at water intakes and critical flow velocity for bed movement


Event

Discharge

(cfs)

Velocity

(ft/s)

Depth

(ft)

Median
grain size

(mm)

Critical Flow Velocity (ft/s)

Incipient Bed
Movement
6
-
10

Small Degree of
Bed Movement
11

Significant Bed
Movement
12

50% Exceed

7,911

0.7
-
1.8

9
-
16

0.38

0.9
-
1.8

2.6
-
3.2

3.1
-
4

90% Exceed

18,500

1.5
-
4

10
-
16

0.38

0.9
-
1.8

2.7
-
3.2

3.2
-
4

2
-
yr

54,951

5
-
7

14
-
20

0.38

0.9
-
1.8

3
-
3.4

3.8
-
4.7

5
-
yr

87,067

7
-
10

17
-
22

0.38

1
-
1.9

3.2
-
3.7

4.2
-
4.9

10
-
yr

107,881

7.5
-
10.5

18.5
-
25

0.38

1
-
1.9

3.3
-
3.9

4.5
-
5.3

100
-
yr

232,500

8
-
10

30
-
35

0.38

1
-
2.1

4
-
4.2

5.7
-
6


The 50%
Exceedance

Event

has a velocity range that corresponds to incipient bed movement.

For the
90% Exceedance event the velocity range falls within all three critical flow ranges depending on the
location of the point near the intakes.

The velocity ranges for t
he 2
-
yr, 5
-
yr, 10
-
yr and 100
-
yr floods are
above the significant bed movement range. Therefore significant bed movement should be expected in
that region for these flows.

At the 90% Exceedence flow and above the majority of the reach is in the
significant
bed movement velocity range or above.


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For the lower flows (7,911 and 18,500) there are some pronounced shadowing effects resulting
in
lower
velocities behind the intakes on the lee (downstream side) of the structures that are below the given
velocity ran
ges above in Table 3. This effect happens for all of the flows

modeled. For
the 2
-
yr flow and
above the velocities are above the significant bed movement threshold.

50 Percent
Exceedance

Flood Event

The 50% Exceedance Flow Condition is defined as the discharge in the river that is greater than 50% of
the discharges for the period of record. This discharge was defined for the flow simulations as 7,911 cfs
with a WSE of 813.5 ft controlled by the gates.

The AdH results for the Existing Condition Geometry,
velocity and depth plots for the entire modeled domain are given below in Figures 15 and 26.
Velocity
and Depth plots for the stretch of the river that coincides with the proposed project improvements is

given in Figures 1
7

and 1
8

respectively.
The
Velocity and Depth plots near the intakes are shown below
in Figures, 1
9

and
20

respectively.

Figure
15
: Velocity Entire Reach (ft/s)


Figure
16
: Depth Entire
Reach (ft)






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Figure
17
: Velocity (ft/s)




Figure
18
: Depth (ft)




Figure
19
: Velocity Near Intake (ft/s)



Figure
20
: Depth Near Intake
(ft)







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90 Percent Exceedance Flood Event

The 90% Exceedance Flow Condition is defined as the discharge in the river that is greater than 90% of
the discharges for the period of record. This discharge was defined for the flow simulations as 18,500
cf
s. The downstream boundary was controlled by the gates at Bowersock Dam to an elevation of 813.5
ft.
The AdH results for the Existing Condition Geometry, velocity and depth plots for the entire modeled
domain are given below in Figures 21 and 22.

Figure
21
: Velocity Entire Reach (ft/s)


Figure
22
: Depth Entire Reach (ft)




The
Velocity and Depth plots near the intakes are shown below in Figures,
23

and
24

respectively.
Velocity and Depth plots for the stretch of the river that coincides with the proposed project
improvements is given in Figures
25

and
26

respectively.

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Figure
23
: Velocity near Intake (ft/s)


Figure
24
: Depth near Intakes (ft)


Figure
25
: Velocity (ft/s)




Figure
26
: Depth (ft)



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2yr

Flood Event

The 2yr Flood Event Discharge has a 1 in 2 probability of occurring during a given year.
The

discharge
for
the 2
-
Yr Event was defined as 54,951ft with a downstream WSE of 816.11 ft.
The AdH results for the
Existing Condition Geometry, velocity and depth plots for the entire modeled domain are given below in
Figures
27 and 28
.

Figure
27
: Velocity Entire Reach (ft/s)




Figure
28
: Depth Entire Reach (ft)





The
Velocity and Depth plots near the intakes are shown below in Figures, 2
9

and
30

respectively.
Velocity and Depth plots for the stretch of the river that coincides with the proposed project
improvements is given in Figures
31

and
32

respectively.



Northwest Hydraulic Consultants

DRAFT

Kansas River KAW Intake Sedimentation Study

20

July 11, 2012


Figure
29
: Velocity (ft/s)






Figure
30
: Depth (ft)




Figure
31
: Velocity near Intakes (ft/s)



Figure
32
: Depth near Intakes (ft)






Northwest Hydraulic Consultants

DRAFT

Kansas River KAW Intake Sedimentation Study

21

July 11, 2012