SEDIMENTATION STUDY
Tributary 0056
Kenmore, Washington
Prepared for: City of Kenmore
6700 NE 181st Street, Kenmore WA 98028
Prepared by: Herrera Environmental Consultants
2200 Sixth Ave, Suite 1100, Seattle WA 98028
**ALL DOCUMENTS ARE IN PDF FORMAT AND MAY BE SLOW TO LOAD**
Section 1 - Contents
Executive Summary - v
Introduction - 1
Purpose of Study - 1
Effects of Urbanization on Watershed Sediment Production - 1
Watershed Characterization - 7
Delineation of the Watershed Boundary - 7
Description of Watershed Development - 8
Classification of Current Land Cover - 11
Fish Usage and Habitat within the Tributary 0056 Watershed - 12
Evaluation of Sediment Production - 19
Findings of Stream Channel Reconnaissance - 19
Watershed Runoff Model - 32
Assessment of Particle Mobility and Sediment Transport - 38
Summary of Watershed Sediment Production - 43
Management Strategies for Reduced Sediment Production, Transport, and Deposition - 47
Stream Channel and Bank Stabilization - 47
Stream Channel Grade Control - 47
Bank Stabilization - 49
Tightlining of Drain Pipes on Higher Eroding Slopes - 49
Modifications to the Mouth of the Stream - 51
Basin Runoff Management - 52
Maintenance and Enforcement of Requirement for Level 2 Stormwater Flow Control Standards - 52
Maximization of Stormwater Infiltration and Dispersion - 52
Retrofits for Regional Stormwater Detention Facilities - 53
Increased Enforcement of Erosion and Sediment Controls at Construction Sites - 53
Coordination with Other Jurisdictions - 53
Implementation Costs for Management Alternatives - 54
Installation of Stream Channel Grade Controls - 54
Stabilization of Eroding Banks - 55
Tightlining of Drainage Outfalls on Eroding Slopes - 55
Level 2 Flow Control at Development Sites - 55
Installation of Stormwater Infiltration and Dispersion Systems - 56
Regional Stormwater Detention Facilities - 56
Increased Erosion and Sediment Control Inspections at Construction Sites - 56
Coordination with Other Jurisdictions - 57
Recommended Action Plan - 57
Funding for Recommended Action Plan - 58
Stormwater Management Fees - 61
Local Improvement District Fees - 61
Grants - 61
Cost Sharing among Jurisdictions in the Watershed - 61
References - 63
Appendix A - Historical Basin Development Images
Figure Number Description
Figure A-1 Historical aerial photograph from 1944
Figure A-2 Historical aerial photograph from 1953
Figure A-3 Historical aerial photograph from 1965
Figure A-4 Historical aerial photograph from 1979
Figure A-5 Historical aerial photograph from 1988
Figure A-6 Historical aerial photograph from 1990
Figure A-7 Historical aerial photograph from 1995
Figure A-8 Historical aerial photograph from 2002
Appendix B - Photographic Characterization of the Tributary 0056 Stream Network
Photo Log
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure
12
Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
Figure 23
Appendix C - Stream Survey and Sediment Sample Results
Appendix D - Hydrology Model Setup and Sediment Mobility Calculations
Appendix E - Preliminary Cost Estimates for Structural
Appendix F - Grant Fund Alternatives
Tables
Table 1. Percentages of total watershed area and total stream length within each
jurisdiction. ....................................................................................................................8
Table 2. Percentages of low-density development, high-density development, and
forested land cover within the Tributary 0056 watershed for each year,
according to aerial photographs...................................................................................12
Table 3. Percentage of total impervious area for each land cover class. ...................................12
Table 4. Percentages of land cover types and total impervious area in the Tributary
0056 watershed based on 1998 Landsat imagery. .......................................................17
Table 5. Tributary 0056 stream segment description.................................................................20
Table 6. Classification of channel response type.......................................................................26
Table 7. Guidelines for determining the stages of channel evolution........................................26
Table 8. Protocol for determining bank stability. ......................................................................27
Table 9. Protocol for determining streambed gravel cementation/armoring. ............................28
Table 10. Descriptions of current priority sediment sources. a ....................................................29
Table 11. Locations of surveyed channel cross-sections and sediment sample sites. .................30
Table 12. Grain-size distribution of bulk sediment source samples. ...........................................30
Table 13. Grain-size distribution of pebble count and instream bulk sediment samples.............37
Table 14. Modeled storm flow results for Tributary 0056 (flows in cubic feet per
second). ........................................................................................................................38
Table 15. Input parameters used in sediment transport calculations for Tributary 0056.............43
Table 16. Largest mobile particle sizes for modeled recurrence interval streamflows at
three cross-section locations on Tributary 0056, using two methods (Shields
and MPM). ...................................................................................................................44
Table 17. Estimated percentage of total input bedload transported through each reach
and deposited in each reach for a range of recurrence interval flows..........................44
Table 18. Estimated cost of sediment and stormwater control measures for priority
sediment source locations. ...........................................................................................65
FIGURES
Figure 1. Tributary 0056 study area. .............................................................................................3
Figure 2. Detail map of the mouth of Tributary 0056 showing the extent of dredging
activities. ........................................................................................................................5
Figure 3. Redefined Tributary 0056 watershed boundary and the extent of storm drain
data................................................................................................................................9
Figure 4. Summary of watershed development over time...........................................................13
Figure 5. Current land cover from the 1998 Landsat image. ......................................................15
Figure 6. Stream segment locations. ...........................................................................................21
Figure 7. Channel response types for surveyed stream segments. ..............................................23
Figure 8. Models for determining channel evolution. .................................................................25
Figure 9. Priority sediment source locations and reaches. ..........................................................31
Figure 10. Current channel evolution and bank stability. .............................................................33
Figure 11. Locations of surveyed cross-sections and sediment sample sites................................35
Figure 12. Subbasin land cover in the Tributary 0056 watershed.................................................39
Figure 13. Geologic map of the Tributary 0056 watershed. .........................................................41
Figure 14. Conceptual estimate of historical sediment production rates for the Tributary
0056 watershed. ...........................................................................................................46
Figure 15. Typical log and boulder weir in stream channel..........................................................50
Figure 16. Typical cross-section of vegetated geogrid bank stabilization. ...................................52
Figure 17. Locations for potential sediment and stormwater control measures in the
Tributary 0056 watershed. ...........................................................................................63
iv9
|
