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Floodproofing study & outfall system plan (OSP) Update

City of Englewood

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PROJECT CONCLUSIONS

Floodproofing Conclusions:

After researching existing topography and structures, looking at flood history, creating hydraulic models, reaching out to homeowners, and research other publications on floodproofing we have formulated the following conclusions:

 

Strong confirmation of significant and frequent flooding in the area was found in the hydrology and hydraulic calculations, in the public outreach and comments, in site visits, in the photographic record, and in discussions with homeowners.

Hydrology and Hydaulics confirm that even in a 5-year event flood waters are inundating a number of streets and reaching home foundations as well as out buildings.

Floodproofing of individual homes is feasible for the majority of homes that are in inundation zones.

For homes in the deepest inundation locations, the most cost effective floodproofing methods are unadvisable, and only raising the home above the inundation level would provide adequate protection.  Raising the home involves jacking, retrofitting the foundation, and retrofitting the architecture, making it expensive and complicated.

Most homes in inundation areas are eligible for flood insurance through the National Flood Insurance Program.

Homeowners will need assistance in developing plans for floodproofing, and will need good mapping resources to help them understand their risk.

A number of reported flooding locations are just outside of the inundation areas reflected in the hydrology and hydraulic calculations.  This confirms that the granularity of the analysis, that is the amount of detail built into the modelling, does not have sufficient detail to account for all types of flooding.  Specifically, street flooding near the downstream end of basins where more detailed street capacity calculations would be needed is not reflected, and flooding caused by additional obstructions such as sewer plugging, and solid fencing is not reflected.

 

 

Recommendations

The City has begun the process of addressing flooding, the first step being this study and public outreach.  This process will involve many specific actions over a long period of time.

 

Based on our floodproofing study we are making the following recommendations:

  • A public outreach program should be developed to help residents understand their flood risk and assist them in evaluating the need for flood insurance in their location.

  • A public education and outreach program should be developed to assist homeonwers with floodproofing.

  • Utilization of basements within flood inundation areas can be a high life safety risk, depending on the level of inundation and level of basement ceiling, as well as the physical abilities of the occupants.  The City should contemplate a program of outreach to these homeonwers, and consider building and occupancy restrictions in inundation zones.

  • The City might consider other assistance in the form of grants and matching funds to assist homeowners financially

  • Homes in the deepest inundation areas, say exceeding 3’ of inundation will need special attention.  Programs such as City buy back through a bond issue or assessment would likely be needed to generate the needed funds.

  • Solid fencing within inundation areas is creating diversions that exacerbate flooding on surrounding properties.  The City should consider changes to its fence ordinance to restrict solid fencing in inundation areas.

  • Additional detail should be added to hydrology and hydraulic calculations near the downstream end of basins since we have noted locations where additional street flooding is occurring that is not indicated in the current models.

OSP Conclusions

After researching existing storms, looking at flood history, creating hydraulic models, reaching out to homeonwers, and exploring alternative infrastructure improvements we have formed the following conclusions:

 

  • Strong confirmation of significant and frequent flooding in the area was found in the hydrology and hydraulic calculations, in the public outreach and comments, in site visits, in the photographic record, and in discussions with homeowners.

  • Hydrology and Hydaulics confirm that even in a 5-year event flood waters are inundating a number of streets and reaching home foundations as well as out buildings.

  • Floodproofing of individual homes is feasible for the majority of homes that are in inundation zones.

  • A number of reported flooding locations are just outside of the inundation areas reflected in the hydrology and hydraulic calculations.  This confirms that the granularity of the analysis, that is the amount of detail built into the modelling, does not have sufficient detail to account for all types of flooding.  Specifically, street flooding near the downstream end of basins where more detailed street capacity calculations would be needed is not reflected, and flooding caused by additional obstructions such as sewer plugging, and solid fencing is not reflected.

  • A plan to provide 100-year infrastructure does not appear to be feasible, although given enough funding a solution could be developed.  Our conclusion was that due to the size of a 100-year system the associated cost of pipe construction, modifications to existing utilities, and disruption to services, it is not practical to construct.  For this reason we did not pursue that alternative in detail, but rather focused on more frequent flood events.

  • Inadequate sized storm collection and piping system is the main cause of flooding of homes.  This situation can be improved dramatically by constructing an expanded, larger sewers system.

  • Virtually all of the existing storm pipes would need to be upsized.

  • In locations where the deepest flooding is projected, additional actions above and beyond sewer capacity improvement would be needed to protect homes from damage and to protect life safety of occupants.

  • We found no reasonable locations where new detention ponds would provide significant reduction in flood hazard.  In locations where Detention could be supplied, many homes would need to be acquired to create new large tracts for installation of ponds, so this alternative was not pursued.

 

OSP Recommendations

Prioritize projects in accordance with this study.  The decision on whether to prioritize other projects over the Oxford pipe will require input from the City Council.

 

Discuss with the City the need for some more detailed hydraulics in a few specific locations where reported flooding is not reflected by the hydraulic model.

 

Develop an alternative “transformative project” as discussed with the City council that has significant drainage and parks benefits and creates a new open space drainageway from Broadway to Navajo Street.  Estimate numbers of houses to be acquired.

 

Discuss whether to proceed with a 100-year estimate for comparison purposes.

 

Develop codes and policies for building on lots that are in the inundation zone.

 

Develop a public information process that conveys information to citizens about flood hazard, home safety planning, floodproofing, and related topics.

The Recommendations and Conclusions for this report are currently in DRAFT format. No recommendations will be made or finalized until the City has provided review and input.

RAW DATA

The following documents are copies of all workbooks, in-field notes, survey results, and other useful information that was used in the compilation of these results.

 

This is the raw field data for the 702 households/businesses that were visited in-person. This document outlines the address, important features (for flooding) of the building/lot, property and life safety risks, and comments about the property.

 

NOTE:

A property was categorized "low life safety risk" if flooding was not an issue or if floodwaters would be below the main floor level and no basement was present. 

A property was categorized "moderate (MID) life safety risk" if floodwaters were high enough to be above the main floor up to 2' and no basement is present or a basement was present but had lower risk of being flooded/had egress windows.

A property was categorized "high life safety risk" if a basement was present with risk of full-inundation (floodwaters to ceiling) with only interior stair egress available or if a basement was not present but floodwaters were between 2-4' on the main level of the home. 

A property was categorized "critical life safety risk" if floodwaters reached more than 4' on the property, if an exterior stairwell to the basement was the only visible source of egress from the basement, if the basement had risk of full inundation with heavy/deep flooding on the main level, or there was another anomaly with the property that would make escape from flooding dangerous or high risk. 

This document is the raw data from the survey sent to 4,000 residents. 55 residents responded to this survey, answering questions such as details on the extent of flooding at their property, the history of floods at the property, the extent of damage, remediation measures applied, and contact information.

 

NOTE: This document was edited only to remove strong language.

These results were used to help compile the Flood Outreach document (see right). 

These are copies of the notes taken in the field during the property walk-by visits. Some common abbreviations/keys to note are:

  • red or green L or P or at risk (red) or not at risk (green) life and property safety

  • WW - window well

  • G - garage,

  • CS - crawl space

  • FV - flood vents, and

  • CL - chain link fence

Each sheet has a keymap showing its location within the basin. Each house within the basins has a white circle with a number inside indicating the expected depth of floodwaters based on the 1999 study interpolations. These depths were used to estimate where on the home (from the lowest grade point on the home) floodwaters will reach. This helped to determine the flood damage risk for each home. 

This is a brief soils report for the study area as provided by the United States Department of Agriculture Natural Resources Conservation Service (NRCS)

This document is the full, report-style version of the pipe assessment report.

Letters were mailed to individual homeowners to obtain more information on flooding that occurred at individual properties, as well as the impact of that flooding. 

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Limitations of Report

  • The statements, conclusions, and recommendations offered in this report are based on information gathered as part of a desktop review and initial field investigations. Additional investigations are required to fully understand the condition of the system evaluated.

Discussions With FEMA

On March 08, 2019, the Calibre team participated in a phone conversation with two representatives from FEMA. This discussion centered around flood insurance, grants for the city, as well as other regulations. Below is a summary of the main points of the discussion. 

Flood Insurance

Anyone is Eligible for Flood Insurance
  • Anyone can get flood insurance, regardless of floodplain location (or lack thereof). 

  • Max coverage of $250,000 with a rate of ~$500 per year, and prices go down from there depending on value of home, SFHA location, etc.

  • Restrictions to obtaining flood insurance include:

    • If the structure is more than 50% below ground

    • If the structure is built completely over water

    • Basement contents are not covered in NFIP. Electrical and mechanical items (furnace, water heater, etc) are covered, but other items (couches, TV etc) are not covered. 

  • Some private insurance companies provide flood insurance. If not, NFIP through the federal government is available. Private insurance has different rules, however, and could drop coverage for any reason. Flood insurance could not be cancelled by the insurer if it is through NFIP.

  • Retrofitting of basements is more expensive and harder than floodproofing a new build, but it is possible.

  • In the SFHA, residential basements cannot be floodproofed, but commercial basements can be retrofitted.

  • Englewood is not in a SFHA and therefore retrofitting is allowable. 

POTENTIAL GRANTS

Pre-Disaster Mitigation Assistance Program
  • The PDM Program, authorized by Section 203 of the Robert T. Stafford Disaster Relief and Emergency Assistance Act, is designed to assist States, U.S. Territories, Federally-recognized tribes, and local communities in implementing a sustained pre-disaster natural hazard mitigation program.

  • The goal is to reduce overall risk to the population and structures from future hazard events, while also reducing reliance on Federal funding in future disasters.

  • This program awards planning and project grants and provides opportunities for raising public awareness about reducing future losses before disaster strikes.

  • PDM grants are funded annually by Congressional appropriations and are awarded on a nationally competitive basis.

  • FEMA requires state, territorial, tribal, and local governments to develop and adopt hazard mitigation plans as a condition for receiving certain types of non-emergency disaster assistance, including funding for PDM mitigation projects.

  • Project subapplications submitted for consideration for PDM funding must be consistent with the goals and objectives identified in the current, FEMA-approved State or Tribal (Standard or Enhanced) hazard mitigation plan along with the local or tribal hazard mitigation plan for the jurisdiction in which the activity is located.

  • Planning subapplications submitted for consideration for PDM funding must result in a mitigation plan adopted by the jurisdiction(s) and approved by FEMA.

Eligibility: The following are eligible Applicants to the PDM grant program:
  • States

  • U.S. Territories

  • Federally-recognized tribes

  • Local governments

Local governments are eligible Subapplicants and can sponsor applications on behalf of homeowners to submit to the Applicant.

Application Process:
  • Subapplicants (i.e., local governments) submit mitigation planning and project subapplications to their State during the open application cycle. After reviewing planning and project applications to determine if they meet the program’s requirements, the Applicants (i.e,. States, U.S. Territories, or Federally-recognized tribal governments) prioritize and forward the planning and project applications in a PDM grant application to FEMA.

  • Locals (subapplicants) should contact their State Hazard Mitigation Officer or Federally-recognized tribal/local government official to obtain detailed information on the PDM application process.

  • Colorado State Hazard Mitigation Officer

Steven Boand, Disaster Recovery Manager

Colorado Division of Homeland Security and Emergency Management

9195 E Mineral Ave, #200, Centennial, Colorado 80112

Phone: (970) 385-1675 ext. 518306694, Fax: (720) 852-6750

E-Mail: steven.boand@state.co.us 

Web Page: www.dhsem.state.co.us

  • Once FEMA reviews planning and project applications for eligibility and completeness, FEMA makes funding decisions based on the agency's priorities for the most effective use of grant funds and the availability of funds posted in the Notice of Funds Opportunity (NOFO) announcement on Grants.gov.  The PDM program is a highly competitive grant program.

  • FEMA awards PDM funds to State, U.S. Territory, and Federally-recognized tribal Applicants, who in-turn provide subawards to local government Subapplicants.

FY 2019 Application Cycle:

FEMA will offer NOFO webinars, which is usually in Aug thru Sep, for potential applicants (States) prior to opening the application period, which is usually from Oct 1st thru Jan 31st.

The Colorado Division of Homeland Security and Emergency Management (DHSEM) encourages local communities throughout the State interested in learning more about this opportunity to contact one of the State Hazard Mitigation Specialists listed below for additional information. 

DHSEM is requiring sub-applicants use EMGrants to notify DHSEM of formal interest in submitting a sub-application for grant funding.  Interested sub-applicants are encouraged to contact a Mitigation Specialist to determine if an active account in EMGrants exists or if a new account is required.

Below were the important DHSEM deadlines for FY 2018:

August 14, 2018 - Initial Notification to DHSEM of Project/Plan Interest

October 17, 2018 - Draft Benefit-Cost Analysis (BCA) Submitted to DHSEM for Review EMGrants

November 16, 2018 - Preliminary Application due to DHSEM via EMGrants

January 14, 2019 - Final Applications Submitted to DHSEM in eGrants

May 1, 2019 - FEMA Anticipated Funding Selection Date

December 30, 2019 - FEMA Anticipated Award Date

PDM projects for FY 2018 are capped at $4 million Federal share (with the exception of Resilient Infrastructure projects, which are capped at $10 million Federal share); communities may exceed this amount, but all additional costs will not be subject to the 75 percent Federal / 25 percent local cost share, and all costs exceeding this amount must be borne by the local community. 

Advance Assistance: For the first time, FEMA is offering Advance Assistance grants under both PDM and FMA (Flood Mitigation Assistance).  These grants are capped at a Federal share of $200,000 for PDM and $100,00 FMA. Advance Assistance can be used to develop mitigation strategies and obtain data to prioritize, select, and develop and design community mitigation projects and other related activities.

Standards & Resources

Resources used in preparing this website:

  • US Army Corps of Engineers. Flood Proofing Techniques, Programs, and References. Omaha: US Army Corps of Engineers, 2000. (pp. 1–32).

  • FEMA. FEMA P-259: Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures. FEMA, 2012.

  • FEMA. FEMA P-312: Homeowner’s Guide to Retrofitting: Six Ways to Protect Your Home from Flooding. FEMA, 2014.

  • MegaSecur-WaterGate. “MegaSecur | Products.” Retrieved 2018 10 25 from: www.megasecur.com/en/products/

  • US Army Corps of Engineers. Flood Proofing Regulations. Washington DC: Army Corps of Engineers, 1995. (pp. 1–85).

  • WMGB Home Improvement. “Advantages of Basement Egress Windows.” Retrieved 2018 10 15 from:
    www.wmgb.com/egress-windows/advantages-basement-egress-windows/

Previous Studies

Wright-McLaughlin Engineers. Project No. 9203 Harvard Gulch Flood Control $2,300,000 General Obligation Bond Issue. Sponsored by City and County of Denver Department of Public Works Engineering Division. Summer 1967.

Sellards & Grigg. Englewood, Colorado Storm Drainage Plan. Sponsored by Urban Drainage and Flood Control District. January 1971.

Gingery Associates. Flood Hazard Delineation Harvard Gulch, West Harvard Gulch, & Dry Gulch. Sponsored by Urban Drainage and Flood Control District, City and County of Denver, and Arapahoe County. December 1979.

Turner Collie & Braden. City of Englewood Outfall Systems Planning Alternatives Evaluation Report. Sponsored by City of Englewood and Urban Drainage and Flood Control District. February 1998.

Turner Collie & Braden. City of Englewood Probable Areas Affected by Flooding from the 100-Year Storm. Sponsored by Urban Drainage and Flood Control District and City of Englewood. March 1998.

Turner Collie & Braden. City of Englewood Outfall Systems Planning Preliminary Design Report. Sponsored by City of Englewood and Urban Drainage and Flood Control District. September 1999.

Matrix Design Group. City and County of Denver Storm Drainage Master Plan. Sponsored by City and County of Denver. September 2014.

 

Matrix Design Group. Harvard Gulch and Dry Gulch Major Drainageway Plan. Sponsored by Urban Drainage and Flood Control District, City and County of Denver, and City of Englewood. December 2016.

Matrix Design Group. Flood Hazard Delineation Harvard Gulch and Dry Gulch. Sponsored by Urban Drainage and Flood Control District, City and County of Denver, and City of Englewood. February 2017.

 

Published June 11th, 2019