7-DOE Swano 2019 Inspection Report.pdf

2019 Periodic Inspection Report

Swano Lake Dam Grays Harbor County, Washington

April 2020 DSO File GH 22-0547

2019 Periodic Inspection Report Swano Lake Dam

Contact Information For more information contact:

Water Resources Program Dam Safety Office P.O. Box 47600 Olympia, WA 98504-7600 Phone: 360-407-7122

Washington State Department of Ecology — www.ecology.wa.gov

Dam Safety Office staff contact information – https://ecology.wa.gov/Water- Shorelines/Water-supply/Dams/Emergency-planning-response#dscontact

Dam Safety Office guidance information – https://ecology.wa.gov/Water- Shorelines/Water-supply/Dams

To request ADA accommodation including materials in a format for the visually impaired, call Ecology at 360-407-6872 or visit https://ecology.wa.gov/accessibility. People with impaired hearing may call Washington Relay Service at 711. People with speech disability may call TTY at 877-833-6341.

http://www.ecology.wa.gov/ https://ecology.wa.gov/Water-Shorelines/Water-supply/Dams/Emergency-planning-response#dscontact https://ecology.wa.gov/Water-Shorelines/Water-supply/Dams/Emergency-planning-response#dscontact https://ecology.wa.gov/Water-Shorelines/Water-supply/Dams https://ecology.wa.gov/Water-Shorelines/Water-supply/Dams https://ecology.wa.gov/accessibility

2019 Periodic Inspection Report

Swano Lake Dam Grays Harbor County, Washington

The dam safety inspection of Swano Lake Dam, engineering analyses, and technical material presented in this report were prepared under the supervision and direction of the undersigned professional engineers, in accordance with RCW 43.21A.064(2).

Martin Walther, P.E.

Hydrology/Hydraulics Engineer Dam Safety Office Water Resources Program

April 2, 2020 (date signed)

Jintae Lee, Ph.D., P.E.

Geotechnical Engineer Dam Safety Office Water Resources Program

April 2, 2020 (date signed)

Madison Lyon, EIT, contributed the dam breach flood maps and the DSS-WISE dam breach flood study in Appendix D.

This page is purposely left blank.

DSO File GH 22-0547 i April 2020

Table of Contents Page

List of Figures and Appendices .......................................................................................... ii Figures........................................................................................................................... ii Appendices .................................................................................................................... ii

Introduction

Project Information

Background

Previous Inspection Summary

Field Inspection

Reservoir

Embankment, Abutments, and Foundations

Internal Seepage/Drainage Controls

Principal Spillway

Auxiliary Spillway

Low Outlet – Water Supply

Instrumentation

Evaluation and Analysis

Condition Assessment

Downstream Hazard Assessment

Hydrology and Spillway Adequacy

Embankment Stability

Operation and Maintenance

Emergency Preparedness

Annual Inspections

Remedial Actions Required

Remedial Actions

References

Bibliography

Additional Resource Material

DSO File GH 22-0547 ii April 2020

List of Figures and Appendices

Figures Figure 1: Vicinity Map Figure 2: Site Plan

Appendices Appendix A: Project Data Sheet

Appendix B: Photographs

Appendix C: Engineering Drawings

Appendix D: Flood Maps and Dam Breach Flood Report

DSO File GH 22-0547 1 April 2020

Introduction In accordance with RCW 43.21a.064(2), the Department of Ecology, Dam Safety Office (DSO) has the responsibility and authority to inspect the construction of all dams and other works related to the use of water, and to require necessary changes in construction or maintenance to reasonably assure safety to life and property. This report has been prepared in accordance with this statute.

The purpose of this report is to present the results of an inspection of the Swano Lake Dam. The report provides some background information and a description of the project; results of the June 18, 2019, inspection; and remedial actions based on the findings.

Project Information

Background Swano Lake Dam is located in western Grays Harbor County, on the south side of Aberdeen at Grays Harbor College. The reservoir and dam are owned and operated by Grays Harbor College.

The reservoir is used for aquaculture, irrigation, and recreation.

Previous Inspection Summary The previous periodic inspection was performed on March 6, 2014, with a follow-up inspection on April 30, 2015, (Satterthwaite, 2015). The following deficiencies were observed and noted in a preliminary results letter dated May 13, 2015:

1. Principal spillway impeded by debris and sediment.

2. Vegetation at emergency spillway entrance.

3. Lush vegetation on downstream face, may indicate seepage.

4. Update Operation and Maintenance Plan.

5. Perform annual dam inspections (by owner).

6. Update Emergency Action Plan.

7. Perform updated hydrologic analysis (by DSO).

DSO File GH 22-0547 2 April 2020

Field Inspection The primary field inspection of the Swano Lake Dam was performed on June 18, 2019. The DSO inspection team consisted of the following personnel:

Name Aspects Covered

Martin Walther, P.E. Coordinator, Hydrology/Hydraulics Jintae Lee, Ph.D., P.E. Geotechnical

Janet Parker of Grays Harbor College assisted during the early part of the inspection.

Reservoir At the normal pool operating elevation of 36.0 feet, the reservoir has a surface area of 4.0 acres and holds a volume of 60 acre-feet. At the auxiliary spillway overflow elevation of 37.0 feet, the reservoir has a surface area of 4.2 acres and holds a volume of 64 acre-feet. At the dam crest elevation of 40.0 feet, the reservoir would have a surface area of 5.2 acres and would hold a volume of 78 acre-feet.

Embankment, Abutments, and Foundations The Swano Lake Dam is an earth embankment 24 feet high and 300 feet long. The dam has a drained buttress on the downstream face to control seepage through the embankment. The dam also serves as a road embankment with a paved road on the dam crest.

At the time of our field inspection, the embankment appeared to be well-maintained and in Satisfactory condition, with no safety deficiencies noted this time. Our visual observations did not notice any indications of settlement, cracking, sinkholes or other depressions, or soil move-ment. The upstream face has a band of thick vegetation along the water edge that seems to be providing adequate protection against wave erosion.

For earth embankments such as this one, vegetation control is a major maintenance and safety issue. Grounds crews at the College have been doing a good job of maintenance and vegetation control on the dam, although we did notice one area that needs additional attention and effort. At the downstream toe of the dam around the outfall for the auxiliary spillway pipes, the brambles and other thick vegetation need to be cut away from the rock splash pad at the spillway outfall.

This effort is needed to provide better access to this area for inspection of the spillway outfall and splash pad, and also to locate the drain outfall for the drained buttress.

On the downstream face, we did notice several small holes and mounds that may be evidence of burrowing animal activity. These areas should be monitored for possible animal activity, and may need repair as needed at some time in the future. If burrowing problems become extensive, the animal burrows should be backfilled with well compacted structural fill to prevent additional erosion; and a program to control the animal population should be instituted and clearly described in the Operation and Maintenance (O&M) manual for the facility.

DSO File GH 22-0547 3 April 2020

Internal Seepage/Drainage Controls Internal drainage for the embankment is provided by a drained buttress on the downstream face.

Seepage is collected by perforated pipes 6 inches in diameter set into a buried cut-off trench filled with pea gravel. The cut-off trench runs near the downstream toe of the dam for the entire length of the embankment. Collected seepage discharges from a PVC pipe 6 inches in diameter to the downstream end of the rock splash-pad at the outfall for the auxiliary spillway pipes.

We were not able to locate the drain outfall due to brambles and other thick vegetation at the outfall for the auxiliary spillway pipes, so this feature could not be inspected this time. However, we did not notice indications of unusual seepage at the toe of the embankment or near the abutments, so the drained buttress seems to be intercepting any seepage that occurs through the embankment. The DSO should be notified immediately if any signs of instability or indications of unusual seepage are observed. The thick vegetation also needs to be trimmed to allow visual inspection of the embankment as mentioned in the previous section.

Principal Spillway The principal spillway is a concrete drop structure 8 feet x 4 feet x 8 feet high, located at the left abutment. The intake structure is drained by a HDPE slip-lined pipeline 24 inches in diameter and 150 feet long which conveys flows through the embankment.

The principal spillway appeared to be in Satisfactory condition, with no safety deficiencies noted this time, although the interior of the intake structure was not accessible for inspection.

The concrete of the intake structure appeared to be somewhat weathered, but in satisfactory condition. The interior of the outlet pipe through the embankment was not inspected this time, although there were no deficiencies visible from the pipe outfall.

Grounds crews at the College have been doing a decent job of vegetation control at the spillway entrance. The spillway entrance was open and unobstructed this time.

The concrete of the stilling basin at the pipe outfall appeared to be somewhat weathered, but in satisfactory condition, although our inspection of the right and downstream exterior sides of the concrete basin was hampered by brambles and other thick vegetation. The brambles and thick vegetation need to be cut away from the right and downstream exterior sides of the stilling basin to provide better access to these sides of the concrete basin for inspection.

Auxiliary Spillway The auxiliary spillway is a concrete drop structure 24 feet x 7 feet x 7 feet high, located at the center of the dam. The intake structure is drained by three HDPE slip-lined pipes 39 inches in diameter and 100 feet long which convey flows through the embankment.

The auxiliary spillway appeared to be in Satisfactory condition, with no safety deficiencies noted this time. The concrete of the intake structure is still in good condition. The interiors of the outlet pipes through the embankment were not inspected this time, although there were no deficiencies visible from the pipe outfalls.

DSO File GH 22-0547 4 April 2020

Grounds crews at the College have been doing a decent job of vegetation control at the spillway entrance. The spillway entrance was open and unobstructed this time.

The pipe outfalls to the rock splash pad were accessible for inspection, but inspection of the downstream extent of the rock splash pad was hampered by brambles and other thick vegetation.

The brambles and thick vegetation need to be cut away from the rock splash pad to provide better access to the entire splash pad for inspection, and also to locate the drain outfall for the drained buttress.

As will be discussed in a later section of this report, the Swano Lake spillways do not have adequate capacity to pass the dam safety inflow design flood (IDF). Calculations by DSO found that the spillways could accommodate the runoff from a Design Step 4 dam safety storm without overtopping the dam. However, based on new awareness of the possible extent of flooding from a dam failure, Design Step 8 will be required for the Swano Lake Dam spillways. This issue will be discussed further in a later section of this report.

Low Outlet – Water Supply The water supply low outlet is a PVC pipeline 12 inches in diameter. According to the engineering drawings for the dam, the intake is located near the center of the dam out in front of the intake structure for the auxiliary spillway. According to the drawings, the pipeline conveys water 150 feet to a 4 ft x 4 ft concrete vault located at the toe of the dam to the left of the stilling basin for the principal spillway. The vault is located outside the fence that surrounds the aqua-culture building. A similar 4 ft x 4 ft concrete vault is located at the upstream edge of the dam crest. The tops for both vaults are level with the ground surface. Both vaults have metal lids.

The drawings do not indicate how these vaults are related to the outlet pipe, only that the plan views show the pipe passing through each vault. The drawings in DSO files also do not show the piping from the downstream vault into the aquaculture building.

At the time of our inspection, we noticed the presence of these concrete vaults with metal lids, but did not recognize their association with the water supply outlet pipeline, so we neglected to ask the College staff to open the vaults for our inspection.

This water supply outlet pipeline appears to be the only permanent feature that would allow dam operators to drop the reservoir water level below the overflow elevation for the principal spillway. The ability to drain the reservoir in an emergency and reduce water pressure on the embankment, at least partially, is an important dam safety feature. Depending on the piping within the aquaculture building, it appears that the water supply outlet piping might also be able to serve as the reservoir drain for the dam.

DSO will need more information about the water supply piping to and within the aquaculture building to verify whether this outlet pipe could serve as a reservoir drain, and also to estimate the drawdown capability of this pipeline. We also need more information about the two concrete vaults and how these vaults relate to the low outlet pipeline, and information about any flow control valves or other flow control features associated with this pipeline.

DSO File GH 22-0547 5 April 2020

Instrumentation At this time, there is no formal instrumentation at this dam. It is our understanding that water level within the reservoir is currently noted in relation to existing site features including the spillway and dam crest. At a minimum, a reservoir staff gauge should be installed in a readable location to monitor the water level within the reservoir.

Evaluation and Analysis

Condition Assessment Based on observations made during the inspection, the condition assessment of the dam is considered to be Poor. This condition assessment is in line with the system used by the National Inventory of Dams to classify dams with a dam safety deficiency recognized for loading conditions which, may realistically occur and remedial action is necessary. The primary reasons for this rating are insufficient spillway capacity and lack of an updated Emergency Action Plan.

Downstream Hazard Assessment A downstream hazard classification of Hazard Class 1A - High downstream hazard potential is assigned to the Swano Lake Dam. This is a major change from the previous downstream hazard class for this dam. The current estimate is that as many as 190 residences may be at risk from a dam breach flood.

New computerized analytical capabilities allow better consideration of downstream flood routing and mapping of possible flood inundation areas compared to previous analyses by DSO. An updated dam failure analysis for Swano Lake Dam indicates additional flood areas compared to previous studies, which in turn changed the downstream hazard class compared to previous determinations.

The flood from a potential dam failure would travel overland north and northeast for 1.2 miles toward the Chehalis River. The downstream area is a medium density suburban area with associated residential property and transportation features that surrounds the college campus on the north and northeast sides. The Grays Harbor College aquaculture building is located immediately below the dam. After that, the dam breach flood would cross the campus parking lot and athletic field, then overflow into a wooded area immediately north of the campus and toward the east to flood a residential area in the vicinity of Huntley, Lewis, Evans and Harriman Streets.

The latest flood analysis estimates that the dam breach flood would attenuate within the residential area, and would not extend to the Chehalis River.

The first inhabited structure that would be hit by a dam breach flood is the aquaculture building immediately below the dam. Flood travel time to this structure is approximately 1 minute.

The downstream flood path and the location of the residential area that may be at risk from a dam breach flood are shown on maps compiled by DSO that may be included in the Emergency

DSO File GH 22-0547 6 April 2020

Action Plan (EAP) for the dam. Copies of these maps are shown in Appendix D, along with a copy of the DSS-WISE dam breach flood study. The EAP is a separate stand-alone document.

Hydrology and Spillway Adequacy At this time, the spillways for Swano Lake Dam can pass the runoff from a Design Step 4 dam safety storm without overtopping the embankment. The Step 4 event has an annual exceedance probability of 1 in 10,000, and an exceedance probability of 1 in 200 over a 50-year period, so the likelihood of a storm this size occurring within the next few years is quite low.

Unfortunately, considering the increased hazard class discussed in the previous section, capacity for a Step 4 storm does not meet DSO requirements. With the increased hazard class and a larger population at risk, the spillways for Swano Lake Dam must be able to pass the runoff from a Design Step 8 event. An updated hydrologic analysis was performed to investigate this further.

At the location for Swano Lake, the rainfall statistics are such that the storm rainfalls for Step 6, Step 7, Step 8, and Probable Maximum Precipitation (PMP) are all numerically equal. One ramification of this is that further refinement of the dam breach flood might be able to reduce the Design Step to Step 7 rather than Step 8, but ultimately this would not affect the size of design storm for the dam safety inflow design flood. One other ramification of this is that the inflow design flood for dam safety will also be the Probable Maximum Flood (PMF), the largest flood that DSO would require for spillway design regardless of the downstream hazard.

Of the three dam safety storm scenarios, DSO’s analysis found that the Intermediate storm would be the controlling event. The Intermediate storm PMP has a total storm rainfall of 11.61 inches during the 18-hour storm duration. The PMF from this storm has a runoff volume of 294 acre-feet from the watershed and a peak flow of 437 cfs into the lake. The runoff volume is 79 percent of the storm rainfall volume.

Flood routing through the reservoir found just minimal attenuation of the flood peak discharge, with a combined peak flow of 434 cfs through the spillway and over the dam. With a maximum capacity of 338 cfs through the spillway, the remaining 96 cfs would overtop the embankment.

Analysis of the outflow hydrograph calculated by the computer model found that flows would overtop the dam for more than 3 hours, with a maximum overtopping depth of almost 9 inches.

With the roadway across the top of the embankment, it does not appear that the dam has any good locations to install additional spillway capacity without very major disruptions to the dam.

An alternative to adding spillway capacity would be to armor the dam crest and downstream face such that the dam could withstand overtopping flows. The situation at Swano Lake Dam is similar to the situation at the SW Genesee Street Dam in west Seattle, where articulated concrete blocks were used to armor the downstream face of the dam to allow the embankment to with-stand overtopping flows during extreme storm events.

The armoring at SW Genesee Street is offered for illustrative purposes only. Calculations by DSO estimate that overtopping protection for Swano Lake Dam must be able to accommodate flows of up to 96 cfs and withstand flow velocities of up to 9 ft/sec. Any armoring that can provide this same level of protection would be acceptable.

The final design for the armoring on the downstream face, or other alternatives to provide additional spillway capacity, will require the services of a Professional Engineer to design the

DSO File GH 22-0547 7 April 2020 improvements and to supervise the installation. The College will need to provide or hire these engineering services, similar to previous improvements to the dam and spillways.

Embankment Stability As part of the 2019 Periodic Inspection, a review of the dam safety documents regarding the Swano Lake Dam was performed. Based on the record drawings and previous stability analysis review, the typical section of embankment slope and height is judged acceptable. No evidence of past or present instability was noted, as there have not been changes to the static and seismic loading conditions and to the physical elements of the embankment. Further, the embankment appeared to be well constructed and maintained, and seemed to be performing satisfactorily.

By virtue of the lack of visible defects, the slope stability of the embankment is judged to be adequate at this time.

Operation and Maintenance The Operation and Maintenance (O&M) Plan, previously compiled in 1999, needs to be updated.

In order to meet the requirement of the more comprehensive O&M Manual, DSO has updated the O&M Plan template to include more detailed information. Within the next 180 days of receipt of this report, please use this new template to update the O&M Plan and send a copy to Jodi Goodman, DSO Compliance Technician at jodi.goodman@ecy.wa.gov. The new template can be found at https://fortress.wa.gov/ecy/publications/documents/ecy07039.pdf.

The O&M Plan should also be checked regularly and updated with current contact information, and to confirm that the procedures for routine maintenance, inspection and monitoring are up to date. Although we do not require a full O&M Manual for this dam, Ecology’s Publication 92-21, Guidelines for Developing Dam Operation and Maintenance Manuals, provides information that may be helpful when filling out the O&M Plan template.

If you have questions regarding the O&M Plan, please contact Jodi Goodman at 360-407-6613 or jodi.goodman@ecy.wa.gov.

Emergency Preparedness The Emergency Action Plan (EAP) for Swano Lake Dam needs to be updated, especially in light of the increased downstream hazard classification for the dam. An EAP based on the simplified EAP form available from the Dam Safety Office web site would suffice. Please contact Charlotte Lattimore, DSO’s EAP Coordinator, for additional information and guidance for updating the EAP. Charlotte can be reached by e-mail to charlotte.lattimore@ecy.wa.gov or by phone at 360-407-6066. When it becomes available, DSO will need a copy of the updated Emergency Action Plan for our files.

As mentioned previously, maps of the dam breach flood path and the residential areas that may be at risk are shown in Appendix D.

mailto:jodi.goodman@ecy.wa.gov https://fortress.wa.gov/ecy/publications/documents/ecy07039.pdf mailto:jodi.goodman@ecy.wa.gov mailto:charlotte.lattimore@ecy.wa.gov

DSO File GH 22-0547 8 April 2020

Annual Inspections A periodic inspection of the dam should be conducted by the dam owner on an annual basis and the findings recorded on an inspection form included in the O&M Plan. A copy of the completed annual inspection documentation should be submitted to Jodi Goodman – DSO Compliance at jodi.goodman@ecy.wa.gov. DSO has not received the completed annual inspection documentation for the past five years.

Remedial Actions Required

Remedial Actions Below is a list of actions that the owner(s) must take to address the deficiencies we found during our inspection and described throughout this report. These deficiencies must be addressed to meet dam safety guidelines. Within 60 days after receiving this report, please respond to Jodi Goodman, DSO Compliance, by email at jodi.goodman@ecy.wa.gov or by letter with a plan and a timeline for completing the tasks listed below.

1. Emergency Action Plan: Update EAP, send copy to DSO. This is especially important in light of the increased downstream hazard classification for the dam.

2. Dam O&M Plan: Update O&M Plan, send copy to DSO.

3. Embankment Overtopping Protection: Design and install overtopping protection for the embankment, or additional spillway capacity. This work will require supervision by a Professional Engineer.

4. Principal Spillway outfall: Cut thick vegetation around stilling basin for spillway outfall on right and downstream sides of concrete stilling basin.

5. Auxiliary Spillway outfall and embankment toe: Cut thick vegetation at toe of slope around rock splash pad for spillway outfall; locate drain outfall for drained buttress.

6. Seepage Monitoring: After drained buttress drain outfall is located, monitor drain discharge for flow rate and clarity or cloudiness.

7. Embankment: Monitor burrowing animal activity, repair animal holes as necessary.

Minor 20

8. Low Outlet piping: Compile information on piping system from lake into and within aquaculture building, send copy to DSO.

9. Instrumentation: Install reservoir staff gauge to facilitate water level readings.

10. Annual inspections by dam owner: Perform annual inspections, send inspection report form to DSO.

DSO File GH 22-0547 9 April 2020

Reminder: In performing these required remedial actions for the dam, the dam owner is still responsible for complying with other applicable local, state, and federal requirements, including compliance with environmental review and permitting requirements. Please refer to the Governor’s Office for Regulatory Innovation and Assistance - ORIA website for more information.

(https://www.oria.wa.gov/site/alias__oria/368/Home.aspx)

References

Bibliography Johnson, D.L., and J.M. LaVassar. First Periodic Dam Safety Inspection Report, Swano Lake Dam (unpublished report in file no. GH 22-0547). Washington State Department of Ecology, Dam Safety Office. May 2006.

USACE. National Inventory of Dams, US Army Corps of Engineers, Washington DC. Version 4.0, Page 16. April 2008

Additional Resource Material Water Resources Program, Dam Safety Section. Dam Safety Guidelines, Part I: General Information and Ownership Responsibilities. Washington State Department of Ecology Publication No. 92-55A. July 1992.

(available at: https://fortress.wa.gov/ecy/publications/summarypages/9255a.html)

Water Resources Program, Dam Safety Section. Dam Safety Guidelines, Part II: Project Planning and Approval of Dam Construction or Modification. Washington State Department of Ecology Publication No. 92-55B. February 2008.

(available at: https://fortress.wa.gov/ecy/publications/documents/9255b.pdf)

Water Resources Program, Dam Safety Section. Dam Safety Guidelines, Part III: An Owner’s Guidance Manual. Washington State Department of Ecology Publication No. 92-55C. July 1992 (available at: https://fortress.wa.gov/ecy/publications/summarypages/9255c.html)

Water Resources Program, Dam Safety Section. Dam Safety Guidelines, Part IV: Dam Design and Construction. Washington State Department of Ecology Publication No. 92-55D. July 1993.

(available at: https://fortress.wa.gov/ecy/publications/summarypages/9255d.html)

Water Resources Program, Dam Safety Section. Guidelines for Developing Dam Operation and Maintenance Manuals. Washington State Department of Ecology Publication No. 92-21.

https://www.oria.wa.gov/site/alias__oria/368/Home.aspx https://www.oria.wa.gov/site/alias__oria/368/Home.aspx https://fortress.wa.gov/ecy/publications/summarypages/9255a.html https://fortress.wa.gov/ecy/publications/documents/9255b.pdf https://fortress.wa.gov/ecy/publications/summarypages/9255c.html https://fortress.wa.gov/ecy/publications/summarypages/9255d.html

DSO File GH 22-0547 10 April 2020

February 1995 (available at: https://fortress.wa.gov/ecy/publications/SummaryPages/92021.html)

Water Resources Program, Dam Safety Section. Guidelines for Developing Dam Emergency Action Plans. Washington State Department of Ecology Publication No. 92-22. February 1995.

(available at: https://fortress.wa.gov/ecy/publications/documents/9222.pdf)

Federal Emergency Management Agency. Technical Manual for Dam Owners, Impacts of Animals on Earthen Dams. FEMA Publication No. 473. FEMA. September 2005.

(available at: http://www.swc.nd.gov/pdfs/impacts_animals_earth_fema473.pdf)

Federal Emergency Management Agency. Technical Manual for Dam Owners, Impacts of Plants on Earthen Dams. FEMA Publication No. 534. FEMA. September 2005. (available at:

https://www.fema.gov/media-library-data/20130726-1446-20490-2338/fema-534.pdf)

Water Quality Program. 2019 Stormwater Management Manual for Western Washington.

Washington State Department of Ecology Publication No. 19-10-021. July 2019. (available at:

https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/Content/Resources/Docs ForDownload/2019SWMMWW.pdf) https://fortress.wa.gov/ecy/publications/SummaryPages/92021.html https://fortress.wa.gov/ecy/publications/documents/9222.pdf http://www.swc.nd.gov/pdfs/impacts_animals_earth_fema473.pdf https://www.fema.gov/media-library-data/20130726-1446-20490-2338/fema-534.pdf https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/Content/Resources/DocsForDownload/2019SWMMWW.pdf https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/Content/Resources/DocsForDownload/2019SWMMWW.pdf µ

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WATER RESOURCES PROGRAM

DAM SAFETY OFFICE

2019 Periodic Inspection Report Swano Lake Dam

Grays Harbor County, Washington

VICINITY MAP

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WATER RESOURCES PROGRAM

DAM SAFETY OFFICE

2019 Periodic Inspection Report Swano Lake Dam

Grays Harbor County, Washington

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DSO File GH 22-0547 14 April 2020

2019 Periodic Inspection Report – Appendix A Swano Lake Dam

DSO File GH 22-0547 A-1 April 2020

Appendix A: Project Data Sheet

General

State I.D. No. GH 22-0547

Owner and Operator Grays Harbor College

Location T 17 N, R 9 W, Section 16 South side of Aberdeen at G.H. College Lat 46.954 deg N / Long 123.801 deg W

Construction Completed 1950

Major Modifications 1990 (install drained buttress, auxiliary spillway) 1995 (slip-line principal spillway) 2007 (slip-line auxiliary spillway

Purpose Aquaculture; irrigation; recreation

NID Condition Assessment Poor (inspected June 2019)

Downstream Hazard Potential 1A - High

Downstream Flood Path Overland northeast toward Chehalis River

Reservoir

Watershed Swano Lake watershed Drainage Area 0.6 square miles

Normal Pool Operating Elevation 36.0 feet Surface Area at Normal Pool 4.0 acres Active Storage at Normal/WQ Pool 60 acre-feet

Spillway Overflow Elevation 37.0 feet Surface Area at Spillway Overflow 4.2 acres Active Storage at Spillway Overflow 64 acre-feet

Dam Crest Elevation 40.0 feet Surface Area at Dam Crest 4.8 acres Active Storage at Dam Crest 78 acre-feet

DSO File GH 22-0547 A-2 April 2020

Dam Embankment

Type Homogeneous earthfill with drained buttress Structural Height 24 feet Hydraulic Height 24 feet Crest Elevation (typical) 40.0 feet Crest Elevation (minimum) 40.0 feet Elevation Datum Spillway weir = 37.0 feet

Crest Length 300 feet Crest Width 30 feet Upstream Slope 2 H:1V Downstream Slope 3 H:1V

Principal Spillway

Auxiliary Spillway

Type 24 inch diameter HDPE slip-lined pipe with concrete intake structure

Location Left abutment Discharge Capacity 25 cfs at water level 37.0 feet

40 cfs at water level 37.4 feet 46 cfs at water level 39.55 feet 47 cfs at water level 40.0 feet

Overflow Elevation 36.0 feet (estimated) Intake Structure Dimensions 8 feet x 4 feet x 8 feet high Overflow Weir Length 8 feet Discharge Conduit – section 24 inch diameter HDPE slip-lined pipe Discharge Conduit – profile 150 feet long at slope 0.062 ft/ft (6.2%)

Type 3 – 39 inch diameter HDPE slip-lined pipes with concrete intake structure

Location Center of dam Discharge Capacity 178 cfs at water level 38.8 feet

DSO File GH 22-0547 A-3 April 2020

Low Outlet – Water Supply

Seepage Instrumentation and Monitoring

Seepage control features Drained buttress

Seepage measurement type None Seepage measurement location Drain daylights at toe of dam on right side of auxiliary spillway culverts outfall

302 cfs at water level 39.55 feet 338 cfs at water level 40.0 feet

Overflow Elevation 37.0 feet Intake Structure Dimensions 24 feet x 7 feet x 7 feet high Overflow Weir Length 24 feet Discharge Conduit – section 3 – 39 inch diameter HDPE slip-lined pipes Discharge Conduit – profile 100 feet long at slope 0.079 ft/ft (7.9%)

Inflow Design Flood – Discharge 434 cfs (overtops dam) Inflow Design Flood – Storm Step 8, 100% PMP, Intermediate duration storm Inflow Design Flood – Precipitation 6 hr = 6.91 inches, 18 hr = 11.61 inches

(as calculated per Technical Note 3, 2009)

Type 12 inch diameter PVC pipe Location Center of dam near left abutment Discharge Capacity 8 cfs at water level 35.0 feet

6 cfs at water level 33.0 feet Flow Controls Upstream – vault at upstream edge of dam crest

Downstream – vault at downstream toe of dam Intake Elevation 30.0 feet (pipe invert) (estimated) Outlet Conduit – profile 150 feet long at hydraulic slope 0.06 ft/ft (6%) Drawdown Capacity 4 feet/day at water level 35.0 feet

(max drawdown at minimal inflow) 3 feet/day at water level 33.0 feet

DSO File GH 22-0547 A-4 April 2020

2019 Periodic Inspection Report – Appendix B Swano Lake Dam

DSO File GH 22-0547 B-1 April 2020

Appendix B: Photographs

DSO File GH 22-0547 B-2 April 2020

Photo 2: Upstream face, auxiliary spillway; looking right.

Photo 1: Dam crest, looking right.

DSO File GH 22-0547 March 2020B-3

DSO File GH 22-0547 B-4 April 2020

Photo 4: Downstream face and toe, spillway outfalls; looking downstream right.

Photo 3: Downstream face, looking right.

DSO File GH 22-0547 March 2020B-5

DSO File GH 22-0547 B-6 April 2020

Photo 6: Downstream face; hole from burrowing animals.

Photo 5: Downstream face; mounds from burrowing animals.

DSO File GH 22-0547 March 2020B-7

DSO File GH 22-0547 B-8 April 2020

Photo 8: Auxiliary spillway, looking downstream right.

Photo 7: Principal spillway, looking downstream left.

DSO File GH 22-0547 March 2020B-9

DSO File GH 22-0547 B-10 April 2020

Photo 10: Auxiliary spillway intake structure interior, looking left.

Photo 9: Auxiliary spillway intake structure, looking left.

DSO File GH 22-0547 March 2020B-11

DSO File GH 22-0547 B-12 April 2020

Photo 12: Auxiliary spillway pipe outfalls, looking upstream.

Photo 11: Spillway pipe outfalls at downstream toe, looking upstream right.

DSO File GH 22-0547 March 2020B-13

DSO File GH 22-0547 B-14 April 2020

Photo 13: Spillway pipe outfalls at downstream toe, looking downstream.

DSO File GH 22-0547 March 2020B-15

DSO File GH 22-0547 B-16 April 2020

2019 Periodic Inspection Report – Appendix C Swano Lake Dam

DSO File GH 22-0547 C-1 April 2020

Appendix C: Engineering Drawings

DSO File GH 22-0547 C-2 April 2020

N 1,0011.j-

N 900 ' T

- N BD<l.j-

CURVE DATA

G) ; : ��6tci s

T � 73.52

-a � 45 42

�) � : :5g-gg" T = 17.09 L = 34,16 g ,f

,CUTOFF TRENCH SEE

\ SHT.5 FOR DETAIL

SMALL RIP RAP

MAIN CULVERT

SEE SHT 4 FOR

DETAILS

------ -.::40 --

P.C STA 0+ 75 29 /

20"EXTENSION

36" • EX CUL VERT

LEGEND

SOIL BORING

(APPROX.LOCATION)

SET #4 REBAR

REMOVE LGT.STD.FOR CONSlRUCT!ON

REPLACE IN SAME LOCATION

ELECTRICAL CONDUIT

RESTORE IN ORIGINAL CONFIGURATION

CUTOFF TRENCH

SEE SHT.5 FOR DETAIL

SAND BLANKET

MEDIUM RIP RAP

DATUM:

CITY OF ABERDEEN MLLW

TBM "SHOP"EL.52.92(DESIGN

ELEVA llON FROM BJSS PLANS)

.ASSLMED GRID

TBM "SHOP" ---t---, SCRIBED 'X'IN

CONC. FLOOR

SLAB OF SHOP

EL.52.92

(MLLW)

TAPER TO MATCH _/

EXISTING PAVEMENT

� INTAKE STRUCTURE

CLEARING LIMIT -

OVERLAY EXISTING-------

PAv1NG REMOVE POSTS

COVER VAULT

JOB TITLE

R

REALIGN EXIST.\

Pl

AS REQUIRED\

REPLACE STOP LOGS

IN EXISTING INLET.

SEE DETAIL SH T.5

8"0 W.M.

RESTORE TO

ORIGINAL LOCATION

SEE SHT.4 FOR DETAILS

SWANO LAKE

SWANO LAKE DAM

REINFORCEMENT

PROPOSED SITE PLAN

NOTIE: UNDERLAY ALL RIP RAP AREAS

AND RETAINING WALLS WITH FILTER

FABRIC AS PER SPECIFICATIONS.

REVISION

NO. DATE

f' 1,200

20 a 20 c-:-- 2

SCALE: 1 ": 20'

HEAVY DUTY EQUIPMENT SHOP -f' l,100

-f! 1,000

-P 900

CHANGE

JOB'NUMBER

90101

DRAW I NGNAME

DAM

f IELD BOO�

DSO File GH 22-0547 C-4 April 2020 r

--45

--40 ---

- 35

--30

--25

1+00

HJ'

3'

··---------- -·------·-------------------------"APC'.P_"R,cOX�IM::'.Ac.:T.=.E-eCecLE'cA'.'.:R�IN"G_cL�IM'.'.clTccS _____ .;_ _______________________________ �

ELECTRICAL

CONDUIT FIELD

LOCATE -- 1'

FILL

� -�::_PHONE & FIRE ALARM

CONDUIT FIELD LOCATE

--- / �EXISTING DAM SURFACE

-- -32.0

3 -� ···./ 1 L---�--- . . • .. ' . __,-\;'"

------ · · .,. . . . .,,,- "-._ DRAIN SAND -- ...... ----

--� �1.5'

CUTOFF TRENCH - SEE DETAIL

LOCATION AS SHOWN ON PLAN, SHT.3

FILL -----.

10" CRUSHED ROCK 7--

8"' W.M.

FIELD LOCATE

2" CLASS 'B'

ASPHALT CEMENT

FILTER FABRIC _/

j

TYPICAL DAM SECTION

SCALE 1"=5'

1 t

--+----+- 34.B NORMAL DRY SEASON WATER SURFACE

--+---�-34.0 NORMAL WET SEASON WATER SURFACE

---31.0

I

I

; I

SOLT PLATE SEE DETAIL BELOW 1; L

TAPER TO EX!SllNG PAVING

I

!:::(-!1] �x1srnJ� PAVING _/

I 2+00

2"CLASS '8' ASPHALT CEMENT

12"CRUSHED ROCK

PA\/ING

EXISTING GROUND AT

DAM CENTERLINE

DAM CENTERLINE PROFILE

SCALE: H. 1"=20'

V. 1"=5'

MATCH EXISTING PAVING

"' a

3+00

FINAL GRADE

t H

I.

; i ( I

I

I IA

I

!f

2"x6" 112 FAS CEDAR

MILLED HAS SHOWN

M

--- CUT TO LENGHT REQ'D.

� � ''"�"·" 6'±

STOP LOGS

NOT TO SCALE

NOTE: GALVAN12:E AFTER

ASSEMBLY

2� EXTRA STRONG

STEEL PIPE

p□ [�

8-5/8'"

-r

I

I, rni [ CJ L

8-5/B"

3'6" -r

- - � fo.25· , 5'

EX. GROUND/ j - --185

2' i==

----20.0

EL VARIES Jr ·/ _____ """" si>-'°"/.,,,,.

�N-'°" / Q�r_ ___,,,,.,\t a 75' 4 s

1--;:s,-i

--5 EACH fl5's

FULL LENG1H

14 0

NOTE: F1NIS� F'1 ON ALL FORMED

SUREryACES

CUTOFF WALL

NOT to SCALE

I.

N TES: SIDEWALL SLOPES MAY 1.5'

t i

BE INCREASED IF SOIL

STABILITY ALLOWS .

6" PERFORATED AD� PJPE

CUTOFF TRENCH

- NOT - TO SCALE

JOB TITLE

SWANO LAKE DAM

REINFORCEMENT

. DRAWING TITLE

TYPICAL DAM SECTION

AND DETAILS

i::i========:::::=:;========:::/

SOLT PLATE (16 EACH)

NOT TO SCALE

DES I GNED B '---�"-'----

DRAWN BY---"'=---

CHECKED BY _ __:_K�.M�-----

DATE ____ �M�A�Y_1�9�9o�--

SCALE ____ _cA�S�S�HO�WNec,__ __

I

L

JOB NUMBER

90101

DRAWING NAME

DETB

- FIELD BOOK

SHT ..L_ OLl-

JUL OtlSSQ'

DSO File GH 22-0547 C-6 April 2020

C

Tl •--- -·--i;O

, I

7.5'

2' MEDIUM RIP RAP

Fil TER FABRIC

:J l-- 1.5 fll

4�-72�--�-�-�------+--��-------'· __ 25-'--t-------; }�

1.25 1.25

3.28

69.50 oo�sm,r

FACE OF DAM

FILTER FABRIC

30.65

15.32

·1 39.28

/ ' EXIS;TING DAM SURFACE

•LlJM\N\2£D SiEEL PIPE

- _::,-:.:•:::""-"---- NOMINAL 100 L.f.

i 8ARRE.LS 1'.2.% ·--====---------

NiER Al'lD Ef•.S --

SLO� -- -

-- SLOPE WEST BARREL 11 %

30,57

SECTIO� A-A

SCALE 1"=5'

i, 1' SMALL RIP RAP

39.0

28.0

26'

2" IP GALVANIZE[)----<--._

14"<t-<t ;

SEE DETAIL SH·1.3

1'

- BEVEL 4S'

35.0

31.0 30.0

\� EXISTING DAM SURFACE

r36.D

1'

2'x2' ECOLOGY BLOCK

........._,_ 36" ALUM!NAZED STEEL

EXTENSION (20.00')

� EXISTING 36" CMP

_L 1.5

T r- I I I I

MAIN CULVERT �tTAIL SCALE 1"-s' 1

1046.06 N.

4753.67 E.

SPILLWAY

CULVERTS DETAIL

SCALE 1"=5'

JOB TITLE

SWANO LAKE DAM

REINFORCEMENT

SE TION C-C

8.00

SLOPE TO MATCH

EXIST. STREAM BED

§ECTION B-B

SCALE 1"=5'

RAWING TITLE

SPILLWAY PROFILE

AND DETAILS

NOTE: FINISH F2 ON ALL· INTERIOR AND

FORMED EX1ERIOR_,;SpRFACES

' I

2 EA tf 5s 5'-0"

LONG AT 4 LOCATIONS

EACH.

I 9• L# 4's ON 12" CENTERS

BOTH WAYS

INTAKE STRUCTURE - SAFETY & TRASH BARS

NOT TO SCALE

DES I GNED BY J.F.

DRAWN BY ---~"·=cH=·--

CHECKED BY--�K�.M~·---

DATE-----�"�'v�,9=•�0 �_

SCALE _____ A_S_S�HO_�--,--

REVISION

NO. DAT CHANGE

HIGH WATER 38.0

# S's ON 12" CENTER

BOTH WAYS

ALL SIDEWALLS

JOB NUMBER

90101

DRAWING NAME

DETA

FIELD ilobK

DSO File GH 22-0547 C-8 April 2020

, u � z.o i l t r:=:l �\,.., '-""r �'\"'""�

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• D ' 5 :t',6, 35- 1

\).)�VI o

I

� 'I". IS,\-,"'-"",) R4'\ Lot,, p

T-c J:i,,.��\:.c

REPAIR OUTLINE BY SI'rE PLAN LOCATION (see Sketch 1 of 8)

A •• Insert HDPE Liner' & two Grout Tubes; Attach Downstream Bulkhead; Introdu,-::e Grout thru three grout ports; Clean Sediment, any Groi1t Spillage, & all Foreign Material from fish capture pond.

B •• End of 150 L.F. Liner; Attach Upstream Bulkhead.

c •• Remove existing Irrigation Pump, Access Ramp, stop Logs, & all . Trash Rack compommts; Reinstall new Stop Log Channel Guides, Stop Logs, & Trash.Rack (or if authorized, use Alternate Lake Level Control).

D •• Remove hatchery a:tea fencing as required & prepare Liner Insertion staging Area; Restore area to original condition.

E •• Remove Organic Tr,�sh & Install new Access Ramp.

F •• Repair failing ri:prap using Grout material.

G •• Install new 6-foot Chain Link Fence Gate.

H •• Install new Chain Link Fence that matches that existing.

Sw(:�\.-\0 L�'c� s;+-E f\o...h, Re..£ei.\Y'" tv\a...<v.. c� \ v �\."'+

DSO File GH 22-0547 C-10 April 2020 f48 I fjo+e.sl . L ,:;,-.,.o«.\- -h..1o. � <l�e. 2-" ,fi , S c.L,, 40

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I

I

DSO File GH 22-0547 C-12 April 2020

2019 Periodic Inspection Report – Appendix D Swano Lake Dam

DSO File GH 22-0547 D-1 April 2020

Appendix D: Flood Maps and Dam Breach Flood Report

DSO File GH 22-0547 D-2 April 2020

1/3 0/2

F:\

WR

\- D

AM

SA

FET

Y\- Da m Fol de rs\

Gra ys

Ha rbo r C ou nty \Sw ano La ke Da m

- 0

7\E

AP

\20

In un dat ion M ap.

mx d

WATER RESOURCES PROGRAM

DAM SAFETY OFFICE

Swano Lake Dam Grays Harbor County, Washington

DSO File GH22-0547 INUNDATION MAP Figure: 1

MK

L µ

0.05 0 0.05 0.1 0.15 0.2 Miles

Service Layer Credits: Northwest Geomatics, LTD

Legend Streams

Dam Breach Inundation Extent

Approximate Parcel Boundary

Reservoir

First Residence Max Depth - 7.2 inches Flood Arrival Time - 9 minutes

Swano Lake Dam

DSO File GH 22-0547 D-4 April 2020

1/3 0/2

F:\

WR

\- D

AM

SA

FET

Y\- Da m Fol de rs\

Gra ys

Ha rbo r C ou nty \Sw ano La ke Da m

- 0

7\E

AP

\20

In un dat ion M ap.

mx d

WATER RESOURCES PROGRAM

DAM SAFETY OFFICE

Swano Lake Dam Grays Harbor County, Washington

DSO File GH22-0547 FLOOD DEPTH MAP Figure: 1

MK

L µ

0.05 0 0.05 0.1 0.15 0.2 Miles

Service Layer Credits: Northwest Geomatics, LTD

Legend Streams

Flood Depth (ft) Value

11.7612

5.0637 4.61146 4.15921 3.70697 3.23319 2.78094 2.3287 1.87646 1.40268 0.950432 0.498187

0.045943 Reservoir

First Residence Max Depth - 7.2 inches Flood Arrival Time - 9 minutes

Swano Lake Dam

DSO File GH 22-0547 D-6 April 2020

N at io na lC en te rf or Co m pu ta tio na l

H yd ro sc ien ce an d

En gi ne er in g

(N

CC

H E)

T he

U ni ve rs ity of

M iss iss ip pi

FOR OFFICIAL USE ONLY

DSS-WISE™ Lite Flood Simulation Report

Complete breach

Swano Lake 2

WA00547

January 29, 2020

Contact Information:

DSS-WISE™ Lite modeling questions: admin@dsswiseweb.ncche.olemiss.edu

DSS-WISE™ Lite Simulation Report

Table of Contents

1.0 Overview

2.0 Modeling Parameters and Conditions

2.1 Project Information

2.2 Simulation Parameters

2.3 Impounding Structure(s) Characteristics

2.4 Bridge(s) to be Removed

2.5 Reservoir Characteristics

2.6 Failure Conditions

3.0 Automated Data Preparation and Job Flow Summary

3.1 Job Flow Summary

3.2 Reservoir Bathymetry and Filling

3.3 Data Sources

3.4 Digital Elevation Model

3.5 Reservoir Boundary and Breaching Structure

3.6 Reservoir Initial Depth Profile

3.7 Land Use/Land Cover

4.0 Simulation Results

4.1 Simulation Summary

4.2 Land Use and Manning’s Roughness Coefficient for Inundated Area

4.3 Coverage and Sources of DEM Raster Datasets

4.4 Maximum Flood Depth

4.5 Flood Arrival Time

4.6 Computed Breach Hydrograph through the Breaching Structure

4.7 Observation Line Hydrograph(s)

4.8 Downloading Simulation Results

Complete breach

WA00547/26604

ii

1.0 Overview

The Decision Support System for Water Infrastructure Security (DSS-WISE™) is an inte-grated software package combining 2D numerical flood modeling capabilities with a series of GIS-based decision support tools. It was developed by the National Center for Com-putational Hydroscience and Engineering (NCCHE) at the University of Mississippi and was initiated by the US Department of Homeland Security (DHS) Science and Technology Directorate through the Southeast Region Research Initiative (SERRI) Program.

A simplified, and fully automated, version of the DSS-WISE™ software suite (DSS-WISE™ Lite Ver 1.0) was developed on behalf of the US Army Corps of Engineers (USACE) Crit-ical Infrastructure Protection and Resilience (CIPR) Program and the DHS Office of In-frastructure Protection. This simplified dam break flood modeling capability was available to interested parties through the Dams Sector Analysis Tool (DSAT) secure web portal until November 2014. An updated version with more features was developed on behalf of Federal Emergency Management (FEMA) and is available at dsswiseweb.ncche.olemiss.edu.

The DSS-WISE™ Lite software suite, running on NCCHE servers, automatically processes input files for dam-break modeling scenarios submitted by an user. DSS-WISE™ Lite fur-ther simplifies simulations by making several general overarching assumptions in an effort to streamline data preparation and computations.

The results produced by this simplified dam-break flood simulation tool represent a rough approximation. They are not intended to replace more detailed flood inundation modeling and mapping products or capabilities developed by hydraulic and hydrologic engineers and GIS professionals.

The user is, therefore, warned that professional engineering judgment should be used in the interpolation of the results generated by this simplified and automated dam-break flood analysis.

To learn more about DSS-WISE™ and DSS-WISE™ Lite visit us at:

https://dsswiseweb.ncche.olemiss.edu

Complete breach

WA00547/26604

https://dsswiseweb.ncche.olemiss.edu

Disclaimer

The National Center for Computational Hydroscience and Engineering (NCCHE), The University of Mississippi, makes no representations pertaining to the suitability of the re-sults provided herein for any purpose whatsoever. All content contained herein is provided "as is" and is not presented with any warranty of any form. NCCHE hereby disclaims all conditions and warranties in regard to the content, including but not limited to any and all conditions of merchantability and implied warranties, suitability for a particular pur-pose or purposes, non-infringement and title. In no event shall NCCHE be liable for any indirect, special, consequential or exemplary damages or any damages whatsoever, includ-ing but not limited to the loss of data, use or profits, without regard to the form of any action, including but not limited to negligence or other tortious actions that arise out of or in connection with the copying, display or use of the content provided herein.

Elevation Datum

All reported elevations use the North American Vertical Datum of 1988 (NAVD 88).

Complete breach

2.0 Modeling Parameters and Conditions

2.1 Project Information

Project Name: Swano Lake 2 Scenario Name: Complete breach

NIDID: WA00547

Scenario Description: reservoir scenario User e-mail: madison.lyon@ecy.wa.gov

2.2 Simulation Parameters

Simulation distance requested (miles): 30 Simulation cell size requested (ft): 20.0 Simulation duration requested (days): 5

2.3 Impounding Structure(s) Characteristics

Number of Structures: 1

Structure Name: Structure 1 Structure Type: Embankment Hydraulic Height (ft): 24.0 Crest Elevation (ft): 38.0 Length (ft): 535.0

2.4 Bridge(s) to be Removed

Number of Bridges: 0

2.5 Reservoir Characteristics

Selected Reservoir Point (Lati-tude/Longitude):

46.9536701987/-123.800671413

Pool Elevation @ Max Storage (ft): 38.0

Complete breach

Maximum Storage Volume (acre-ft): 76.8 Pool Elevation @ Normal Storage (ft): 34.0 Normal Storage Volume (acre-ft): 60.0

2.6 Failure Conditions

Structure Name: Structure 1 Structure Type: Embankment Failure Mode: Total Dam Breach Breach Type: Embankment Pool Elevation @ Failure (ft): 38.0 Storage Volume @ Failure (acre ft): 76.8 Breach Location (Latitude/Longitude): 46.9543642627/-123.801090623

Complete breach

3.0 Automated Data Preparation and Job Flow Summary

3.1 Job Flow Summary

1. Prepare Digital Elevation Model (DEM) and Land Use/Land Cover (LULC) tiles for the Area of Interest (AOI) based on requested cellsize and maximum downstream dis-tance.

2. Burn U.S. Army Corps of Engineers (USACE) levee lines into DEM for the AOI.

3. Assign Manning’s coefficients based on LULC classifications.

4. Validate user provided simulation input parameters.

5. Remove user identified bridges from the DEM.

6. Estimate reservoir bathymetry.

7. Extend impounding structures if the specified reservoir level cannot be contained.

8. Fill reservoir to specified failure elevation.

9. Prepare boundary condition and all input data for simulation.

Complete breach

3.2 Reservoir Bathymetry and Filling

Figure 1. Stage-Volume Curve for Reservoir

Prototype: Theoretical cubic Hermite spline curve generated from user-provided reservoir elevation and volume information.

Imposed: Measured from reservoir bathymetry after filling to the failure elevation.

The reservoir water surface was detected to be in the DEM, so bathymetry estimation was performed using the prototype stage-volume curve shown above.

User-given Storage Volume at Failure (acre ft): 76.8 Imposed Storage Volume at…