lower white river 2009 to 2016 in-channel sediment monitoring · lower white river 2009 to 2016...

Lower White River 2009 to 2016 In-Channel Sediment

Monitoring

March 2017

Prepared by

Department of Natural Resources and Parks Water and Land Resources Division

River and Floodplain Management Section 201 South Jackson Street, Suite 600

Seattle, WA 98104

Alternate Formats Available

206-477-4800 TTY Relay: 711

Lower White River 2009 to 2016 In-Channel Sediment Monitoring

March 2017

Submitted by:

Terry Butler, Geologist King County Water and Land Resources Division Department of Natural Resources and Parks

Funded by: King County Flood Control District


King County i March 2017

Citation

King County. 2017. Lower White River 2009–2016 In-Channel Sediment Monitoring.

Prepared by Terry Butler, Fred Lott, and Chris Brummer. King County Department

of Natural Resources and Parks. Water and Land Resources Division. Seattle,

Washington.


King County ii March 2017

Table of Contents

1.0 Introduction .............................................................................................................................................. 1

2.0 Methods ...................................................................................................................................................... 3

2.1 In-channel sediment ......................................................................................................................... 3

2.2 Hydraulic Analyses ............................................................................................................................ 5

3.0 Setting ......................................................................................................................................................... 6

3.1 Physical conditions ............................................................................................................................ 6

3.2 Flood hydrology .................................................................................................................................. 6

4.0 Results ......................................................................................................................................................... 8

4.1 2009 to 2016 In-Channel Sediment ............................................................................................ 8

4.1.1. Data from surveyed cross sections ....................................................................................... 8

4.1.2. Sediment volumes and rates..................................................................................................11

4.1.3. Changes in gravel-bar elevations from 2009 to 2016 .................................................13

4.2 Hydraulic response to in-channel sediment changes from 2009 to 2016 .................14

4.2.1. Changes in Water Surface Elevations .................................................................................14

5.0 Key Findings/Next Steps ...................................................................................................................17

6.0 References ...............................................................................................................................................18

Figures

Figure 1. Lower White River channel monitoring vicinity map and study area. ................... 2

Figure 2. Annual peak flows on the Lower White River. Data from Water Year (WY) 1987 through 2009 are from White River near Auburn at A Street USGS gage 12100496. Data from WY 2009 through 2015 are from White River near Auburn at R Street USGS gage 12100490. ............................................................... 7

Figure 3. (on following pages) Change in average channel elevations during individual monitoring periods that cover the years from 2009 to 2016 along the White River (A) between RM 1.8 and RM 5.0, (B) between RM 4.5 and RM 8.0, and (C) between RM 7.5 and RM 10.6 Net change from 2009 to 2016 is indicated by black line. ......................................................................................................... 8

Figure 4. Segment-averaged changes in in-channel sediment along Lower White River during 2009-2012, 2012 to 2014, 2014 to 2016, and net 2009 to 2016: (A) sediment volumes and (B) rates of change in sediment deposition or erosion. ..........................................................................................................................................12


King County iii March 2017

Figure 5. Aerial map of Lower White River from RM 5 to RM 6.3 depicting differences in gravel-bar surface elevations from 2009 to 2016. ..................................................13

Figure 6. Lower White River 2009 to 2016 change in Water Surface Elevation (WSEL) at 4000 cfs and change in average channel elevation. ................................................15

Figure 7. Lower White River channel conveyance capacity in 2009 and 2016,

from RM 4.8 to RM 7.8.........................................................................................................16

Tables

Table 1 Lower White River channel-monitoring cross sections, by river segment and years. ...... 3

Table 2. Segment-averaged changes in channel elevation, and rates of change, in the White

River from 8th

Street Bridge (approx. RM 5.0) to RM 10.6). ........................................11

Appendices

Appendix A: Lower White River 2009 to 2016 channel cross-section data and calculations Appendix B: 2009 to 2016 data compared to previous time periods Appendix C: Aerial images showing changes in gravel-bar surfaces, 2009 to 2016


King County Water and Land Resources Division 1 March 2017

1.0 INTRODUCTION

King County monitors sediment levels in the Lower White River channel as part of an ongoing sediment management program, consistent with provisions of the King County Flood Hazard Management Plan (King County 2006, 2013). This channel monitoring includes the distance from approximate River Mile (RM) 1.83 to RM 10.6 (Figure 1). Sediment levels and sediment management in this part of the White River have been of interest to river and flood managers for over a century. Relevant events and activities through that period include significant river engineering and channelization in the early 1900s, ongoing channel dredging of various extents and intensities through the mid-1980s, and increased flood risks in recent years. Previous studies through this monitoring area evaluate sediment levels and associated flood levels up to and including 2009 conditions. This technical memorandum focuses on in-channel sediment and hydraulic conditions from 2009 to 2016. Data and information from earlier periods is provided for context. The purposes of this technical memorandum are to characterize changes in in-channel sediment levels and hydraulic conditions along the Lower White River from 2009 to 2016, to inform ongoing flood-risk management and the design and construction of flood-risk reduction capital projects in the same area.



Figure 1. Lower White River channel monitoring vicinity map and study area.



2.0 METHODS

2.1 In-channel sediment

Channel cross section surveys All surveys collected elevation data referenced to the NAVD 1988 vertical datum and the NAD 1983 (modified 1991) horizontal datum, recorded in units of U.S. feet units. In all years from 2009 to 2016, the majority of bathymetric (underwater) riverbed elevations were collected using a combination of single-beam sonar and survey-grade GPS. Ground elevations for the out-of-water part of a cross section were determined from LiDAR. Bathymetric data and ground-elevation data were combined to construct the full channel cross section. In each year, some of the cross-section survey data were collected using land-survey methods, i.e., a survey instrument and survey rod. Channel-monitoring cross sections surveyed through the study area are summarized by river segment and years in Table 1. Table 1. Lower White River channel-monitoring cross sections, by river segment and years.

River Segment

Approx RMs

# of Xsecs in 2016

2009

2012

2014

2016

D/S end to 8th Str Bridge

1.83 to 4.99

20 X X X

8th Str Bridge to A Str Bridge

4.99 to 6.33

34 X X X X

A Str Bridge to R Str Bridge

6.33 to 7.60

16 X X X X

R Str Bridge to U/S end (at pipeline)

7.60 to 10.60

17 X X X X

D/S: Downstream. U/S: Upstream. RMs: River Miles. Xsecs: Cross sections. X: Survey data collected

A river segment is defined here as a given length of river, which may or may not exhibit consistent geomorphic conditions, as would a “river reach”. River segment boundaries were located at bridge crossings, which result in river segments that match general areas of interest for sediment and flood management in this study area. Cross sections downstream of RM 4.531 were not surveyed in 2014, so channel changes are calculated in that area for the period of 2012 to 2016 instead of 2012 to 2014 and 2014 to 2016.

Some of channel-monitoring cross sections originally were established in the 1970s by Prych (1988). Others were established in 1996 by the City of Auburn (A Street to R Street) for channel monitoring and in 2007 for hydraulic modeling related to a White River Flood Insurance Mapping Study (Northwest Hydraulic Consultants 2009). King County also has



added cross sections to those from earlier studies for ongoing monitoring of in-channel sediment in this study area. Sources of error based on ground and bathymetric surveys include survey instrumentation, variability of elevation at each point due to channel irregularities, mismatched cross-section locations from year to year, and extraction of elevation data along a cross-section line from a digital bathymetric surface. Sources of error in elevations obtained by LiDAR include those that occur during data acquisition, calibration by ground survey and other functions inherent to laser technology (Watershed Sciences Inc. 2011, Tetra-Tech 2016). Vertical accuracy of LiDAR collected in this study area in 2016 typically was less than one-quarter of one foot in open, non-vegetated areas (Tetra-Tech 2016). However, vertical accuracy decreases in densely vegetated or steep areas and the 2016 LiDAR acquisition specifications allowed vertical accuracy to be met within 30 cm (1 foot). Recognizing such constraints, Latterell et al. (2015) assumed a potential vertical error of +/- 1 foot when comparing digital surfaces generated from LiDAR in a study that monitored channel changes. Considering the various potential sources, Czuba et al. (2010) estimated a cumulative error of +/- 2 feet when comparing cross sections at a given location. Both Prych (1988) and Czuba et al. (2010) caution against focusing on changes at an individual cross section and recommend that changes should exceed the cumulative potential error along a river segment at three or more cross sections before concluding that aggradation or degradation has occurred in a particular area. Cumulative potential errors and the approaches and recommendations from previous similar studies were taken into consideration when interpreting the channel monitoring results in this study. Average channel elevations The average channel elevation of each cross section was calculated by integrating the surveyed elevation data collected from one river bank to the other and dividing the integral by the cross section width, following the methods of Prych (1988) and Czuba et al. (2010). Cross-section width was measured as the distance between the tops of each riverbank because the top of bank is more readily identified than some other feature along the riverbank or toe (Prych 1988) and because the resulting value is based on the full active channel, which is relevant for evaluation of channel effects on flooding. Average channel elevations are included in channel cross-section plots in Appendix A. Sediment volumes and rates Changes in in-channel sediment volumes were calculated using the average-end area computation method (as per Czuba et al. 2010). At each cross section, the vertical difference in average channel elevations from one survey year to the next was multiplied by channel width to determine a change in cross-sectional area between surveys. Changes in cross-sectional areas were averaged at adjacent cross sections and a change in volume was obtained by multiplying by the channel length between each pair of adjacent cross sections. Total net change in volume in each monitoring segment was the summation of all such calculations. Average annual rates of deposition (or erosion) were calculated as the net volume divided by the number of years between surveys.



Changes in gravel-bar surface elevations A digital elevation model of gravel-bar surface elevations was constructed from LiDAR data collected in 2009 and 2016 and elevation differences between surfaces were depicted graphically. Calculation of volumetric changes was not attempted because the elevation changes were less than +/- 1 foot in many areas, and because the area of gravel bars exposed in both years was somewhat limited in some areas.

2.2 Hydraulic Analyses

The same surveyed channel cross sections used for in-channel sediment monitoring were used to create a 1-dimensional HEC-RAS hydraulic model of channel conditions in 2009 and in 2016. The only hydraulically modeled parameters compared from 2009 and 2016 are water surface elevations at a given discharge and channel conveyance capacity. Channel conveyance capacity is defined for this study as the flow that is just contained by the lowest riverbank at any given location. This definition is consistent with the channel conveyance capacities evaluated by Prych (1988) and Czuba et al. (2010). Hydraulic variables such as the Manning’s n roughness coefficient were not changed between model years 2009 and 2016. The only difference between the hydraulic models between the two years was the channel geometries, and that change is taken to represent in-channel sediment changes. All of the hydraulic modeling of 2009 and 2016 channel conditions was done using the Raised Levees feature in the HEC-RAS program, which artificially keeps flow in the channel even if water levels would be high enough to go over bank. This feature inserts a tall, frictionless barrier to overtopping flow at the top of each riverbank at every river cross section. This approach focuses the evaluation on the effects of in-channel changes due to sedimentation or erosion and also eliminates the need to simulate overbank split-flow conditions. The Raised Levee feature results in the modeled water surface elevations of flows that occur above the top of the riverbank being overstated to some undetermined degree. However, that situation has been minimized in this analysis by evaluating water surface elevations at a flow that stays within riverbanks through most of the study area. Hydraulic modeling conducted for this study does not include any detailed analysis of the more complex hydraulics around bridges. Channel conveyance capacity at the bridges in this study area was not characterized in this analysis.



3.0 SETTING

3.1 Physical conditions

Physical conditions of this channel monitoring area have been described in detail in previous studies (Dunne 1984; Collins and Sheikh 2004; Herrera Environmental Consultants 2010; Czuba et al. 2010, 2012). Key characteristics relevant to sediment movement and deposition, both natural and constructed, include: Mount Rainier and other parts of the river basin upstream of this study area contribute

large amounts of sediment to the White River. The White River and other channels draining stratovolcanoes carry the largest sediment loads of rivers in the Puget Sound region. (Czuba et al.2011).

The White River flows through a canyon from Buckley to Auburn and into the upstream part of this study area. At about RM 7.8 the White River emerges from the canyon to flow across its alluvial fan through the rest of the study area and downstream. (See, e.g., Herrera (2010) their Figure 4.)

Channel gradient decreases from the steep flanks of Mount Rainer to about 0.6 percent at the upstream end of the study area. Channel gradient further decreases by about half to 0.3 percent at the King-Pierce County boundary line near RM 5.5

Most of the channel downstream of emergence onto the alluvial fan is confined by constructed levees (Figure A-1). Sediment deposition that naturally occurs with decreasing channel slope on an alluvial fan manifests as vertical accretion within the channel due to this channel confinement.

Channel modifications to reroute the White River and enlarge the Stuck River in the early 1900s resulted in excavation of an estimated 1 million cubic yards from the Lower White River (Roberts 1920). Extensive maintenance dredging occurred in the 1930s (Thomas and Thomson 1936) and dredging operations between the mid-1970s and mid-1980s removed an estimated 780,000 cubic yards (Prych 1988). Channel dredging within the study area ceased in 1987.

Channel surveys from 1977 to 1984 indicate large, negative changes in sediment volume in this same study area (Prych 1988), which is consistent with extensive dredging at the time. Channel surveys from 1984 to 2009 indicate aggradation through much of this study area (Czuba et al. 2010; Herrera 2010), which is consistent with conditions after cessation of dredging.

3.2 Flood hydrology

The Lower White River channel is estimated to have contained a discharge of 20,000 cfs in 1948 when Mud Mountain Dam was completed (USACE 2009). Prych (1988) calculated a channel capacity in 1984 greater than 19,000 cfs through most of this study area, with lower channel capacities (10,000 cfs to 15,000 cfs) at a few locations. The three peak flows in excess of 14,000 cfs between Water Year (WY) 1990 and WY 2007 (Figure 2) did not



cause significant overbank flooding, if any. The extensive flooding over both banks that occurred between A Street to 8th Street in January 2009 during a peak flow of 12,300 cfs is attributed to ongoing channel aggradation (US Army Corps of Engineers 2009; Czuba et al. 2010). Peak flows since 2009 have not exceeded approx. 8,000 cfs in the study area (Figure 2). Hydraulic conditions subsequent to 2009 are described in Section 4.2

Figure 2. Annual peak flows on the Lower White River. Data from Water Year (WY) 1987 through 2009 are from White River near Auburn at A Street USGS gage 12100496. Data from WY 2009 through 2015 are from White River near Auburn at R Street USGS gage 12100490.

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

1985 1990 1995 2000 2005 2010 2015

Dis

char

ge (

cfs)

Water Year



4.0 RESULTS

4.1 2009 to 2016 In-Channel Sediment

4.1.1. Data from surveyed cross sections

Locations of the 87 cross sections surveyed in 2016 are showed in Figure A-1 of Appendix A. Surveyed cross sections and their average channel elevations in 2009, 2011, 2012, 2014, and 2016 are plotted in Figure A-2 of Appendix A. A longitudinal profile of average channel elevations in 2009 and 2016 (Figure A-3 of Appendix A) illustrates the marked decrease in channel slope that occurs through this study area. Increases of 1 foot to 2 feet during 2009 to 2016 are evident in Figure A-3 downstream of about RM 6.5 and little change is evident upstream of R Street through this 7-year period. Data from 1977 and 1984 are included in Figure A-3 for historical context. The longitudinal profile of thalweg elevations for the same periods and extents (Figure A-4) exhibits a similar shape and temporal trends as the average channel elevations. Changes in average channel elevation at each cross section during the individual periods from 2009 to 2012, 2012 to 2014, and 2014 (or 2012) to 2016 are shown in Figure 3 (A, B, and C). Almost all changes during the individual periods downstream of the R Street Bridge (RM 7.6) showed increases in elevation, which indicates deposition, ranging from a fraction of 1 foot to nearly 2 feet. The 2009 to 2016 net change in elevation (black line in Figure 3) through most of the river downstream of R Street increased through a range of less than one-half foot to a maximum of almost 3 feet (near RM 5.5). From the R Street Bridge upstream, most changes during individual periods varied as increases or decreases of a fraction of 1 foot to about 1 foot. The resulting net change from 2009 to 2016 (black line) shows a maximum increase of 1 foot at R Street with general decreases upstream to minimum value of approximately minus 1.5 feet at RM 10.3. Decreases in average channel elevation indicate net erosion.

Figure 3. (on following pages) Change in average channel elevations during individual monitoring periods that cover the years from 2009 to 2016 along the White River (A) between RM 1.8 and RM 5.0, (B) between RM 4.5 and RM 8.0, and (C) between RM 7.5 and RM 10.6 Net change from 2009 to 2016 is indicated by black line.



A

B



Historical context for these channel changes is provided by comparing the net changes from 2009 to 2016 (black line in Figure 3) to net changes observed from 1977 to 2009 in Figure B-1 of Appendix B. Segment-averaged changes in channel elevations in individual periods from 2009 to 2016 upstream of the 8th Street Bridge are summarized in Table 2. Segment-averaged changes were calculated as a distance-weighted mean, for each river segment, of the change in channel elevation at each cross section in that segment. The greatest aggradation consistently occurred in the 8th Street to A Street segment, with most occurring from 2014 to 2016. Channel changes in the A Street to R Street segment also consistently showed aggradation, but at about one-third to one-half of that downstream of A Street. Average elevations upstream of R Street all were negligible or modestly negative. Historical context is provided for segment-averaged changes in the 8th Street to A Street segment (first row of Table 2) by comparison to changes since 1984 in Figure B-2 of Appendix B.

C



Table 2. Segment-averaged changes in channel elevation, and rates of change, in the White River from 8

th Street Bridge (RM 5.0) to RM 10.6.

Change in Channel Elevation (feet) Rate of Change (feet/year)

Net

Net

River 2009- 2012- 2014 - 2009- 2009- 2012- 2014 - 2009-

Segment 2012 2014 2016 2016 2012 2014 2016 2016

8th Str to A Str 0.4 0.1 0.8 1.4 0.1 0 0.4 0.2

A Str to R Str 0.1 0.2 0.3 0.6 0 0.1 0.2 0.1

R Str to RM 10.6 -0.1 0 -0.1 -0.2 0 0 0 0

4.1.2. Sediment volumes and rates

Volumes of sediment deposited or eroded, and associated rates of change, in each river segment during the periods from 2009 to 2016 are shown in Figure 4. The 8th Street to A Street segment experienced the most aggradation of all segments and was aggradational in all individual periods. The highest rate of aggradation occurred in 2014 to 2016 from 8th Street to A Street, at over 30,000 cy/yr. The channel segment between A and R Street Bridges showed increasing aggradation volumes and rates through the 3 individual monitoring periods. The channel upstream of R Street experienced consistent modest net erosion from 2009 to 2016. Historical context is provided by comparing the segment-averaged sediment volumes and rates from 2009 to 2016 (net change in right-hand part of Figure 4) to net changes from 1977 to 1984 (Prych 1988) and 1984 to 2009 (Czuba et al. 2010), in Figure B-3 of Appendix B.



Figure 4. Segment-averaged changes in in-channel sediment along Lower White River during 2009-2012, 2012 to 2014, 2014 to 2016, and net 2009 to 2016: (A) sediment volumes and (B) rates of change in sediment deposition or erosion.

-40,000

-20,000

0

20,000

40,000

60,000

80,000

100,000

120,000

2009-2012 2012-2014 2014- 2016 Net 2009-2016

Cu

bic

Yar

ds

8th to A Str A Str to R Str R Str to RM 10.6

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

2009-2012 2012-2014 2014- 2016 Net 2009-2016

Cu

bic

Yar

ds/

Ye

ar

8th Str to A Str A Str to R Str R Str to RM 10.6

B

A



4.1.3. Changes in gravel-bar elevations from 2009 to 2016

Changes in exposed gravel-bar elevations provide a visual indication of in-channel sediment changes from 2009 to 2016. Figure 5 is an example of the aerial images in Figure C-1 of Appendix C, which cover the study area from approx. RM 3.6 to RM 10.6.

Figure 5. Aerial map of Lower White River from RM 5 to RM 6.3 depicting differences in gravel-bar surface elevations from 2009 to 2016.



The range of colors from yellow to red indicates deposition and greens to blues indicate erosion. No color is shown where the change from 2009 to 2016 was less than +/- 1 foot. Observed changes in gravel-bar elevations through the study area generally corroborate sediment trends measured by other means in this analysis. Deposition is the dominant change from A Street downstream (Panels 1, 2, and 3 of Figure C-1) with elevations increasing by 2 to 4 feet in several locations. Between A Street and R Street, most gravel-bar elevations showed minor changes (Panels 4 and 5 of Figure C-1). Of those elevations in the A Street to R Street segment that did change, most were localized areas of deposition of up to 1 to 2 feet. Upstream of R Street to about RM 9.5, the vast majority of changes in gravel-bar elevations were minor (Panels 6 through 8 of Figure C-1). Upstream of RM 9.5, there also were large portions without much change, but there also was a mixture of erosion and deposition in this area (Panels 8 and 9 of Figure C-1). That the panels of Figure C-1 depict relatively minor changes in gravel-bar elevations from A Street to RM 10.6 while survey-based analyses indicate either moderate deposition (A Street to R Street) or moderate erosion (upstream of R Street) suggests that much of the substantive changes in channel elevations occurred in the underwater portion of the channel. Flows differed from about 900 cfs during acquisition of the 2009 LiDAR and about 1700 cfs in 2016, which likely translates to less than one-half foot difference in water surface elevations, a difference that would have minimal effect on the comparison of the exposed parts of gravel bars in the two years.

4.2 Hydraulic response to in-channel sediment changes from 2009

to 2016

Changes from 2009 to 2016 in modeled water surface elevations and channel conveyance capacity are taken to indicate the hydraulic response to in-channel changes in sediment levels.

4.2.1. Changes in Water Surface Elevations

Changes in water surface elevations (WSELs) were computed for the 4,000 cfs discharge in the HEC-RAS hydraulic model. The 4,000 cfs flow was selected because it stays within both riverbanks through most of the study area (as described further below). From 2009 to 2016, there were marked increases in the modeled WSELs at 4,000 cfs downstream of RM 7; those increases ranged from 2 to 4 feet (Figure 6). From RM 7.0 to RM 8.5, most increases were on the order of 0.5 feet, with a local increase at R Street of almost 2 feet. Upstream of RM 8.5, there were decreases in modeled WSELs ranging from less than one-half foot to more than 2 feet.



Figure 6. Lower White River 2009 to 2016 change in Water Surface Elevation (WSEL) at 4000 cfs and change in average channel elevation.

Figure 6 also depicts the change in average channel elevation (i.e., the black line in Figure 3). Almost all of the changes in WSELs match the direction and magnitude of changes in net change in average channel elevation. The changes in modeled WSELs typically occur a short distance upstream of the corresponding change in channel elevation, which is consistent with the sub-critical flow conditions present through the study area.

4.2.2. Changes in channel conveyance capacity

Channel conveyance capacity is that flow that is just contained by the lowest riverbank at any given location. This definition does not recognize the flow containment and flood protection provided by temporary flood containment structures (called HESCOs) that presently line the right bank from A Street (RM 6.3) downstream to about RM 5.35, and along both banks for a few hundred feet downstream of the 8th Street Bridge.

The 2016 channel conveyance capacity varies considerably through the study area (Figure 7). Figure 7 does not extend upstream of R Street because upstream of about RM 6.8 the conveyance capacity exceeds the maximum modeled flow of 19,000 cfs. There are discontinuous lines that indicate channel conveyance capacity at bridge locations in Figure 7 because bridge hydraulics were not modeled in this study (Section 2.2).



Figure 7. Lower White River channel conveyance capacity in 2009 and 2016, from RM 4.8 to RM

7.8.

Changes in channel conveyance capacity from 2009 to 2016 include the following.

Not far upstream of A Street, conveyance capacity dropped from about 17,000 cfs to about 8,000 cfs.

Through most of the segment between the A Street and 8th Street Bridges, conveyance capacity dropped by about half.

The lowest conveyance capacity in this study area is about 4,000 cfs near RM 5.7, which is significantly decreased from about 8,000 cfs in 2009.

These channel conveyance capacities at top of bank are much less than those that existed in the mid-1980s through early-2000s, as described in Section 3.2.

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8

Ch

an

ne

l C

on

ve

yan

ce

Ca

pa

cit

y (c

fs)

River Mile

2009 2016 Maximum modeled flow

8th St

Bridge County

Boundary

A St

Bridge

R St

Bridge



5.0 KEY FINDINGS/NEXT STEPS

Key findings with regard to changes in in-channel sediment from 2009 to 2016 include: Sediment deposition continues to dominate in-channel changes in the study area

downstream of R Street.

In the 8th Street to A Street segment, 2009 to 2016 rates of deposition approximately equaled, and 2014 to 2016 rates exceeded, the longer-term rates from 1984 to 2009.

In the A Street to R Street segment, 2009 to 2016 deposition rates were less than, and the 2014-2016 rates exceeded, the longer-term rates from 1984 to 2009.

Upstream of R Street, the channel exhibited a range of changes from moderate deposition to moderate erosion. Localized deposition occurred at the R Street Bridge.

In the context of historical changes, channel changes in the study area from 2009 to 2016 are consistent with ongoing response to the extensive dredging of 30 to 40 years ago and the major channelization modifications from the early 1900s.

Key findings with regard to hydraulic changes from RM 4.8 to RM 6.8 through this same period include: Changes in water surface elevations at a discharge of 4,000 cfs appear to be directly

correlated to in-channel sediment levels.

Channel conveyance capacity in the study area generally has decreased markedly during 2009 to 2016.

Greatest decreases in channel capacity occurred between 8 Street and A Street, consistent with greatest volumes and rates of sedimentation.

Channel capacity decreased by about half upstream of A Street.

Channel capacity upstream of RM 6.8 remains at or greater than 19,000 cfs

All channel conveyance capacities were calculated at top of bank and do not recognize the flood containment provided by the temporary flood protection structures (HESCOs) now in place.

King County will continue to conduct regular in-channel sediment monitoring in this Lower White River study area to inform the King County flood-risk reduction program and the design and construction of flood-reduction capital improvement projects in this area.



6.0 REFERENCES

Collins, B.D. and A.J. Sheikh. 2004. Historical channel locations of the White River, RM 5 to

RM 28. King County, Washington. Seattle, Washington.

Czuba, J.A., C.R. Czuba, C.S. Magirl, F.D. Voss. 2010. Channel-conveyance capacity, channel change, and sediment transport in the Lower Puyallup, White, and Carbon Rivers, western Washington. U.S. Geological Survey Scientific Investigations Report 2010-5240.

Czuba, J.A., C.S. Magirl, C.R. Czuba, E.E. Grossman, C.A. Curran, A.S. Gendaszek, R.S.Dinicola.

2011. Sediment load from major rivers into Puget Sound and its adjacent waters.

U.S. Geological Survey Fact Sheet 2011-3083.

Czuba, J.A., C.S. Magirl, C.R. Czuba, C.A.Curran, K.H. Johnson, T.D. Olsen, H.K. Kimball, C.A. Gish. 2012. Geomorphic analysis of the river response to sedimentation downstream of Mount Rainier. Washington. U.S. Geological Survey Open-File Report 2012-1242.

Dunne, Thomas. 1986. Sediment transport and sedimentation between RMs 5 and 30 along

the White River, Washington. Seattle, Washington.

Herrera Environmental Consultants. 2010. Summary of sediment trends, Lower White River: RM 4.44 TO RM 10.60. Prepared for King County River and Floodplain Management Section, Department of Natural Resources and Parks. Seattle, Washington.

King County. 2006. King County Flood Hazard Management Plan. King County Department of Natural Resources and Parks, River and Floodplain Management Section.

King County. 2013. Update to King County Flood Hazard Management Plan. King County Department of Natural Resources and Parks, River and Floodplain Management Section.

Latterell, J., L. Hartema, D. Lantz, D. Eastman, H. Berge, C. Toal. 2015. Lower Tolt floodplain reconnection project, effectiveness monitoring report: Year 5 (2014). King County Water and Land Resources Division. Seattle, Washington. March 16, 2015.

Northwest Hydraulic Consultants. 2009. Floodplain Mapping Study for White River, Zone 2

(RM 5.6 to RM 10.6). King Counties, WA. Prepared for King County River and

Floodplain Management Unit, Water and Land Resources Division, Department of

Natural Resources and Parks. July 2009.



Prych, Edmund. 1988. Flood-carrying capacities and changes in channels of the lower

Puyallup, White and Carbon Rivers: U.S. Geological Survey Water-Resources

Investigations Report 87-4129. Tacoma Washington.

Roberts. W.J. 1920. Report on flood control of the White-Stuck and Puyallup Rivers.

Prepared by Inter-County River Improvement.

Tetra Tech. 2016. 2016 King County WLRD LDAR & Orthoimagery Acquisition Technical

Data Report. King County, Washington State. May 2016.

Thomas, B.P. and R.H. Thomson. 1936. Annual report of the Engineers. Inter-County River

Improvement. January 1936.

U.S. Army Corps of Engineers. 2009. Mud Mountain Dam, White River and Puyallup Rivers

channel capacity study. Seattle, WA. U.S. Army Corps of Engineers.

Watershed Sciences, Inc. 2011. LiDAR remote sensing data collection: King County

Washington. Prepared for the King County Department of Natural Resources and

Parks. July 9, 2011.


King County Water and Land Resources Division A-1 March 2017

Appendix A: Lower White River 2009 to 2016

channel cross-section data and calculations

Figure A-1: White River cross section locations Figure A-2: White River cross-section plots Figure A-3: Longitudinal profile of average channel elevations Figure A-4: Longitudinal profile of thalweg elevations Table A-1: Lower White River changes in sediment volume, 2009 to 2012 Table A-2: Lower White River changes in sediment volume, 2012 to 2014 Table A-3: Lower White River changes in sediment volume, 2014 to 2016



Figure A-1. Lower White River channel cross section locations, RM 1.8 to RM 6.5.



Figure A-1, cont. Lower White River channel cross section locations, RM 6.5 to RM 10.6. Figure A-2. (On following pages) White River channel cross sections surveyed in 2009, 2012, 2014 (where indicated), and 2016. Dashed horizontal lines are calculated average channel elevations. Dashed vertical lines show width of channel used in calculation of average channel elevation in each year.



Figure A-3: Longitudinal profile of average channel elevations along White River from RM 1.8 to RM 10.6 in 1977, 1984, 2009 and 2016.



Figure A-4: Longitudinal profile of thalweg elevations along White River from RM 1.8 to RM 10.6 in 1977, 1984, 2009 and 2016.



Table A-1. Lower White River sediment volumes and rates, 2009 to 2012.

HEC-RAS

River

Station

HEC-RAS

distance to

downstream

cross section

Change in

area at

each cross

section

Average

change in area

at adjacent

cross sections

2009-2012

Change in

volume between

adjacent cross

sections

AVERAGE

ANNUAL

rate of

change

Average

channel

width

Vertical

change at

each cross

section,

2009-2012

(miles) (feet) (sq ft) (sq ft) (cu yd) (cu yd/year) (ft) (ft)

4.531 657 -150 -150 -3658 -1219 292 -0.5

4.6920 850 53 53 1675 558 162 0.3

4.715 121 142 98 439 146 164 0.9

4.941 1193 1307 724 32019 10673 182 0.3

4.978 195 125 716 5180 1727 197 0.6

8th St Bridge

4.998 104 173 149 572 191 224 0.8

5.041 227 302 238 1994 665 377 0.8

5.123 434 81 192 3081 1027 450 0.2

5.197 290 14 14 155 52 478 0.0

5.292 502 108 108 2006 669 293 0.4

5.374 433 29 29 458 153 254 0.1

5.460 454 11 11 191 64 233 0.0

5.517 301 396 396 4410 1470 230 1.7

5.589 380 212 304 4280 1427 226 0.9

5.621 169 103 158 986 329 248 0.4

5.712 480 121 112 1990 663 255 0.5

5.822 581 94 94 2032 677 264 0.4

5.920 517 101 98 1877 626 274 0.4

6.013 491 122 122 2216 739 255 0.5

6.077 338 147 134 1683 561 263 0.6

6.145 359 95 121 1608 536 282 0.3

6.223 412 66 80 1227 409 259 0.3

6.313 475 70 70 1228 409 210 0.3

6.326 69 -9 31 78 26 207 0.0

A St Bridge

6.390 169 117 117 735 245 271 0.4

6.482 485 112 115 2063 688 357 0.3

6.569 462 125 119 2027 676 459 0.3

6.647 409 7 66 997 332 348 0.0

6.761 605 98 52 1172 391 377 0.3

6.891 296 -16 -16 -180 -60 374 0.0

7.001 580 -4 -10 -214 -71 312 0.1

7.087 456 -57 -30 -508 -169 274 -0.2

7.170 435 -96 -76 -1230 -410 244 -0.4

7.252 436 11 -42 -684 -228 237 0.2

7.368 610 27 19 428 143 179 0.4

7.511 757 -49 -11 -319 -106 202 -0.1

7.593 434 75 13 203 68 209 0.4

7.608 79 -47 14 40 13 212 -0.2

R St Bridge

7.716 567 13 -17 -363 -121 224 0.1

7.845 683 -98 -43 -1082 -361 234 -0.4

7.958 595 115 8 186 62 345 0.3

8.111 810 34 75 2240 747 343 0.1

8.269 837 157 96 2961 987 244 0.6

8.418 785 -29 64 1856 619 221 -0.1

8.561 756 13 -8 -235 -78 247 0.1

8.707 766 -30 -9 -251 -84 277 -0.1

8.821 603 6 -12 -276 -92 376 0.0

8.946 662 -182 -88 -2161 -720 372 -0.5

9.125 945 -106 -144 -5036 -1679 276 -0.1

9.311 983 -101 -103 -3760 -1253 257 -0.2

9.477 872 112 6 190 63 658 0.2

9.794 1677 -139 -13 -825 -275 362 -0.4

10.065 1430 124 -7 -381 -127 300 0.4

10.343 1469 -128 -2 -104 -35 423 -0.3

10.596 1331 -191 -160 -7879 -2626 536 -0.4

Length Reach VOLUME RATE

Average

width

Average

vertical

change

(R Miles) Boundaries (cu yd) (cu yd/yr) (ft) (ft)

1.348 RM 4.978 to BNRR/A Street Bridges 37,300 12,433 277 0.43

1.390 A Street to R Street 4,500 1,500 289 0.10

2.880 from R Street to u/s end at 10.596 -14,900 -4,967 347 -0.06

5.618

Total for Entire Study Reach 26,900 13,432




HEC-RAS

River

Station

HEC-RAS

distance to

downstream

cross section

Change in

area at

each cross

section

Average

change in area

at adjacent

cross sections

2012-2014

Change in

volume between

adjacent cross

sections

AVERAGE

ANNUAL

rate of

change

Average

channel

width

Vertical

change at

each cross

section,

2012-2014


4.531 657 56 56 1357 679 292 0.2

4.6290 518 -35 11 204 102 205 -0.2

4.6920 331 -4 -19 -233 -117 162 0.0

4.715 123 39 18 81 40 164 0.2

4.941 1195 115 77 3413 1706 192 0.6

4.978 224 151 133 1105 553 197 0.8

8th St Bridge

4.998 104 260 206 790 395 224 1.2

5.041 227 167 214 1798 899 377 0.4

5.123 433 97 132 2122 1061 450 0.2

5.1420 100 130 114 422 211 466 0.3

5.197 290 139 134 1444 722 478 0.3

5.292 502 -194 -194 -3603 -1801 293 -0.7

5.3110 100 -132 -163 -605 -303 290 -0.5

5.374 333 44 44 547 274 254 0.2

5.460 454 9 9 147 74 233 0.0

5.4882 149 -38 -15 -80 -40 238 -0.2

5.517 152 447 204 1151 575 230 1.9

5.589 380 -308 69 973 487 226 -1.4

5.621 169 -34 -171 -1071 -535 248 -0.1

5.712 480 -5 -19 -343 -171 255 0.0

5.7449 174 3 -1 -5 -3 265 0.0

5.822 407 3 3 43 21 264 0.0

5.920 517 17 10 185 92 274 0.1

5.9390 100 40 29 106 53 257 0.2

6.0035 341 23 32 403 201 260 0.1

6.013 50 -21 1 2 1 255 -0.1

6.077 338 -74 -48 -595 -298 263 -0.3

6.145 359 92 9 120 60 282 0.3

6.223 412 97 95 1442 721 259 0.4

6.2419 100 117 107 396 198 253 0.5

6.313 375 117 117 1626 813 210 0.6

6.326 69 148 132 337 168 207 0.7

A St Bridge

6.3530 170 293 220 176 256 243 1.2

6.390 169 264 278 1745 872 271 1.0

6.482 485 162 213 3825 1913 357 0.5

6.569 462 103 132 2259 1130 459 0.2

6.647 409 158 130 1973 987 348 0.5

6.761 605 236 197 4410 2205 377 0.6

6.8348 390 -50 93 1342 671 392 -0.1

6.891 296 36 -7 -75 -38 374 0.1

7.001 580 18 27 585 292 314 0.1

7.087 456 16 17 284 142 274 0.1

7.170 435 5 10 166 83 244 0.0

7.252 436 63 34 549 274 238 0.3

7.368 610 -25 19 426 213 181 -0.1

7.511 757 22 -2 -51 -25 203 0.1

7.593 434 53 38 604 302 209 0.3

7.608 79 5 29 85 42 212 0.0

R St Bridge

7.716 567 69 37 773 387 224 0.3

7.845 683 19 44 1109 554 234 0.1

7.958 595 -70 -25 -561 -280 345 -0.2

8.111 810 -11 -40 -1208 -604 343 0.0

8.269 837 -30 -21 -636 -318 244 -0.1

8.418 785 -18 -24 -704 -352 221 -0.1

8.561 756 -18 -18 -511 -256 248 -0.1

8.707 766 11 -4 -108 -54 277 0.0

8.821 603 5 8 173 86 376 0.0

8.946 662 -13 -4 -101 -51 372 0.0

9.125 945 -13 -13 -450 -225 281 0.0

9.311 983 1 -6 -211 -105 260 0.1

9.477 872 -24 -11 -369 -185 658 0.0

9.794 1677 -53 -38 -2386 -1193 362 -0.1

10.065 1430 -9 -31 -1638 -819 300 0.0

10.343 1469 1 -4 -227 -113 423 0.0

10.596 1331 -85 -42 -2061 -1031 536 -0.2


Average

width

Average

vertical

change





5.618





HEC-RAS

River

Station

HEC-RAS

distance to

downstream

cross section

Change in

area at

each cross

section

Average

change in area

at adjacent

cross sections

2014-2016

Change in

volume between

adjacent cross

sections

AVERAGE

ANNUAL

rate of

change

Average

channel

width

Vertical

change at

each cross

section,

2014-2016


4.531 657 120 120 2928 1464 292 0.4

4.6290 518 196 158 3033 1516 205 1.0

4.6920 331 129 162 1990 995 162 0.8

4.715 123 101 115 523 261 164 0.6

4.941 1195 234 167 7406 3703 174 0.3

4.978 224 -16 109 906 453 197 -0.1

8th St Bridge

4.998 104 52 18 69 35 224 0.2

5.041 227 182 117 982 491 377 0.5

5.123 434 312 247 3973 1987 450 0.7

5.1420 100 375 344 1273 636 466 0.8

5.197 290 477 426 4569 2284 478 1.0

5.2541 301 337 407 4542 2271 312 1.1

5.2731 100 312 324 1206 603 306 1.0

5.292 100 380 346 1278 639 293 1.3

5.3110 100 402 391 1452 726 290 1.4

5.3361 133 344 373 1830 915 289 1.2

5.3550 100 438 391 1445 722 275 1.6

5.374 100 294 366 1361 680 254 1.2

5.3929 100 219 257 948 474 232 0.9

5.4119 100 415 317 1178 589 218 1.9

5.460 254 409 412 3873 1936 233 1.8

5.4882 150 445 427 2370 1185 238 1.9

5.517 153 -202 121 688 344 230 -0.9

5.589 380 214 6 83 42 226 0.9

5.621 168 178 196 1218 609 248 0.7

5.712 483 119 148 2655 1328 255 0.5

5.7449 174 156 137 885 442 265 0.6

5.822 408 247 202 3043 1522 264 0.9

5.920 516 214 230 4399 2200 274 0.8

5.9390 100 147 180 667 333 257 0.6

6.0035 338 268 207 2596 1298 260 1.0

6.013 50 302 285 527 264 255 1.2

6.077 342 387 344 4364 2182 263 1.5

6.145 356 189 288 3794 1897 282 0.7

6.223 413 67 128 1963 982 259 0.3

6.2419 100 172 120 443 222 253 0.7

6.313 377 194 183 2552 1276 210 0.9

6.326 65 186 190 454 227 207 0.9

A St Bridge

6.3530 170 261 224 207 330 243 1.1

6.390 169 128 194 1219 610 271 0.5

6.482 485 167 148 2652 1326 357 0.5

6.569 462 389 278 4758 2379 459 0.8

6.647 409 185 287 4350 2175 348 0.5

6.761 605 7 96 2152 1076 377 0.0

6.8348 390 353 180 2598 1299 392 0.9

6.891 296 116 234 2569 1284 374 0.3

7.001 580 142 129 2767 1384 315 0.5

7.087 456 28 85 1432 716 274 0.1

7.170 435 -6 11 179 89 244 0.0

7.252 436 -4 -5 -74 -37 238 0.0

7.368 610 4 0 0 0 181 0.0

7.511 757 3 3 96 48 203 0.0

7.593 434 2 3 44 22 209 0.0

7.608 79 250 126 368 184 212 1.2

R St Bridge

7.716 567 68 159 3344 1672 224 0.3

7.845 683 191 129 3272 1636 234 0.8

7.958 595 161 176 3876 1938 345 0.5

8.111 810 23 92 2769 1385 343 0.1

8.269 837 -48 -12 -376 -188 244 -0.2

8.418 785 -1 -24 -704 -352 221 0.0

8.561 756 41 20 561 280 248 0.2

8.707 766 34 37 1059 530 277 0.1

8.821 603 51 42 948 474 376 0.1

8.946 662 148 100 2444 1222 372 0.4

9.125 945 -34 57 2009 1004 281 -0.3

9.311 983 43 5 172 86 260 -0.1

9.477 872 95 69 2230 1115 658 0.1

9.794 1677 17 56 3464 1732 362 0.0

10.065 1430 -244 -114 -6026 -3013 300 -0.8

10.343 1469 -444 -344 -18713 -9357 423 -1.0

10.596 1331 138 -153 -7535 -3767 536 0.3


Average

width

Average

vertical

change





5.618




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King County Water and Land Resources Division B-1 March 2017

APPENDIX B.

2009 to 2016 DATA COMPARED TO PREVIOUS TIME PERIODS

Figure B-1: Net changes in average channel elevation along White River from RM 1.8 to RM 10.6 during periods of 1977 to 2009, 2009 to 2016, and 1977 to 2016.

Channel changes during 1977 to 2009 exhibit similar trends but at greater magnitudes as those since 2009, i.e., aggradation downstream of A Street and degradation upstream of A Street. Combining all channel changes from 1977 to 2016 results in consistent aggradation downstream of A Street, at places in excess of 4 to 6 feet. Combined net channel changes upstream of A Street from 1977 to 2016 have varied from zero change to degradation of as much as 4 feet, with one location of aggradation at RM 10.6.



Figure B-2: Lower White River net sediment deposition between 8th Street (RM 5.00) and A Street (RM 6.33) since 1984. Chris Brummer conducted the analyses to produce this chart.



Figure B-2 provides historical context for the 2009 to 2016 segment-averaged changes in channel elevation between 8th Street and A Street. The “Net Deposition (measured)” points in Figure B-2 for 2009, 2012, 2014, and 2016 are the same as segment-averaged values in the first row of Table 2, all of which were calculated in Tables A-1 through A-3. The “Net Deposition (calculated)” curve was calculated using the mean daily discharges shown in this figure applied to the bedload transport rating curve developed for the White River at R Street USGS gage 12100490 by Czuba et al. (2012) and a relationship between bedload supply and deposition in this reach. The close correlation between calculated and measured net deposition suggests that the bedload-rating curve at R Street and the relationship between bedload supply and deposition accurately represent coarse sediment movement in this area over the past 30 years. The period of time from 1984 to 2016 depicts net deposition approximately since cessation of dredging (i.e., 1987) to the present. Stepwise increases in calculated net deposition generally are coincident with large peak flows through 2009. Although peak flows have stayed in the range of 4,000 to 8,000 cfs since 2009 (Figure 2), net deposition has continued (Figure B-2). The estimated threshold of motion for bedload sediment in the lower White River is 4,000 cfs (Czuba et al. 2012), so coarse sediment still is mobilized and deposited in this river segment at these more moderate peak flows. Overall, the ongoing deposition since 1984 is a response that is consistent with channel conditions following cessation of dredging in this river segment. Those conditions include continuous large annual influx of coarse sediment into a confined channel where the channel slope has been locally decreased (beyond the naturally decreasing slope on the alluvial fan) by the excavation from dredging. Net deposition in the 11 years since 2006 approximately equals the net deposition that occurred in the prior 22 years since 1984.



Figure B-3. Changes in in-channel sediment in in the Lower White River from 1977 to 2016: (A) Volumes and (B) Rates of change in sediment volumes Figure B-3 provides historical context by comparing net volumes and rates of sediment changes from 2009 to 2016 (right-hand part of Figure 4) to corresponding in-channel sediment calculations from 1977 to 1984 (Prych 1988) and 1984 to 2009 (Czuba et al. 2010). The negative values from 1977 to 1984 period indicate extraction or erosion or both, consistent with widespread dredging at that time. From 1984 to 2009, the positive values downstream of R Street indicate sediment aggradation, with an average annual deposition rate of about 8,000 cy/yr to 9,000 cy/yr. The consistently negative values upstream of R Street may result from an upstream knickpoint migration (e.g., subsequent to channel lowering by dredging in downstream areas). Both aggradation downstream of and erosion upstream of R Street during the 1984 to 2009 period are consistent responses to the cessation of dredging in1987.

-600,000

-500,000

-400,000

-300,000

-200,000

-100,000

0

100,000

200,000

300,000

1977-1984 1984-2009 2009-2016 Net 1977-2016

Cu

bic

Yar

ds


-60,000

-50,000

-40,000

-30,000

-20,000

-10,000

0

10,000

20,000

1977-1984 1984-2009 2009-2016 Net 1977-2016

Cu

bic

Yar

ds/

Ye

ar


B

A



Changes from 2009 to 2016 are relatively minor compared to the massively negative volumes and rates from 1977 to 1984 (associated with channel dredging), but 2009 to 2016 aggradation rates equal or exceed aggradation rates during (the post-dredging) 1984 to 2009 period. The combined total from 1977 to 2016 is over 200,000 cubic yards net aggradation in the 8th Street to A Street segment. Net changes between A to R Street from 1977 to 2016 showed modest net losses of sediment through this same 40-year period. The channel upstream of R Street has experienced net erosion of large sediment volumes through the same period.


King County Water and Land Resources Division C-6 March 2017

APPENDIX C CHANGES IN GRAVEL-BAR SURFACE ELEVATIONS 2009 to 2016

Figure C-1: (9 panels on following pages) Deposition and erosion along White River from approx. RM 4 to RM 10.6 on exposed gravel bar surfaces during 2009 to 2016. Blue to green colors indicate erosion and yellow to red colors indicate deposition. Elevation differences calculated only where gravel bars existed and were exposed in both 2009 and 2016.



Figure C-1, panel 1.

lower white river 2009 to 2016 in-channel sediment monitoring · lower white river 2009 to 2016...

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