217217217

200200200

255255255

000

163163163

131132122

2396553

110135120

1129256

62102130

1025648

130120111

237237237

8011927

252174.59

“The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”

Prepared by

Rene Vermeeren, P.E., D. WRE.

Adam Bier, P.E.

PRESENTATION FOR THE POTENTIAL ADDITION OF SPECIAL FLOOD HAZARD AREAS

1

File Name

17 October 2016

Part 1: Summary of Floodplain Analysis for Los Angeles RiverPart 2: Los Angeles County Drainage Area (LACDA) study results

File Name

2

PART 1: SUMMARY OF FLOODPLAIN ANALYSIS FOR LOS ANGELES RIVER

Prepared by Adam Bier, P.E.Senior Hydraulic Engineer

Photo: Los Angeles River showing flows near the top of the channel at Los Feliz Boulevard with debris on the railing (January 26, 1969)

File Name

3PRESENTATION OVERVIEW Study Overview and Project Area Los Angeles River Channel Existing Federal Emergency Management Agency

(FEMA) Floodplain Hydraulic Modeling Overview 100-Year Floodplain Changes in Floodplain Mapping Results and Summary

File Name

4STUDY OVERVIEW AND PROJECT AREA Study Overview Flood Plain Management Services

(FPMS) Study Prepared 100-Year and 500-Year

Floodplain Maps Analysis completed for the City of

Los Angeles

Los Angeles River Study Reach Barham Blvd to First St Approximately 13 miles Main Tributaries:

Burbank Western Verdugo Wash Arroyo Seco

File Name

5LOS ANGELES COUNTY DRAINAGE AREA

File Name

6LOS ANGELES RIVER CHANNEL Topographic Data Sources Overbanks: LARIAC (2006)

Provided by City of Los Angeles

Channel (Concrete): As-built drawings Channel (Earth bottom): 2008 Survey

Corps Topographic Survey

Levees Levees are within study reach Levees extend intermittently from

Burbank Western Confluence south past Glendale Blvd

LARIAC: Los Angeles Region Imagery Acquisition Consortium

File Name

7EXISTING FEMA FLOODPLAIN (100-YEAR) Special Flood Hazard Area (SFHA) Study area currently has 874 parcels in

SFHA in City of Los Angeles 100-Year Flood FEMA Classification Zone A

In channel - west of I-5 FEMA Classification Zone AE

In Channel from Los Feliz Blvd to Arroyo Seco Confluence

Overbank flooding south of Interstate 5 (Arroyo Seco)

FEMA Flood Insurance Rate Maps Effective date: September 26, 2008 Panel Numbers in Study Area 1339F 1345F 1610F

1626F 1628F 1636F

FEMA Flood Map Service Center https://msc.fema.gov/portal

File Name

8HYDRAULIC MODELING OVERVIEW Hydraulic Modeling Software Hydrologic Engineering Center River Analysis System (HEC-RAS) 5.0.1

Models Current Condition of Channel Dense vegetation and sediment in “earth bottom” channel reaches Temporary flood barriers are not modeled

Hydraulic Model Models how water flows down the river and how it overtops out of the Los

Angeles River channel into the Floodplain One Dimensional (1D): Channel Two Dimensional (2D): Overbank areas 27 Bridges in study reach

File Name

9100-YEAR FLOODPLAIN

Google Earth Video, 2016

File Name

10FLOODPLAIN MAP EXAMPLE

File Name

11CHANGES IN FLOODPLAIN MAPPING Existing Flood Insurance Rate Maps (100-Year Flood) Show;

874 City of Los Angeles parcels currently in Special Flood Hazard Area (SFHA)

Difference from the FEMA FIRM and this 2016 Corps FPMS (100-Year Flood) Existing FIRM

373 City of Los Angeles parcels are no longer shown in Floodplain 501 City of Los Angeles parcels are still shown in the Floodplain

2016 Corps FPMS Study Adds: 2,574 City of Los Angeles parcels to the Floodplain Adds: 271 Parcels outside of the City of Los Angeles (Glendale & Burbank) Net Total: 3,075 City Of Los Angeles parcels

Parcel Count: City of Los Angeles Estimates

File Name

12RESULTS Number of Parcels shown Floodplain (100-year)

3,075 City of Los Angeles 271 City of Glendale & City of Burbank

Average Flood Depths 5-10 feet in the floodplain

Approximate Maximum Flood Depth in Overbank 18 feet (Griffith Park)

Approximate Area of Inundation: 1,000 acres Flow is contained in channel downstream of Arroyo Seco

Confluence

File Name

13SUMMARY Corps Study identifies Flood Risk to the public Potential Flooding shown in Bette Davis Park, Griffith Park,

Atwater Village, Elysian Valley & other areas

Next steps Corps study can be used to help develop evacuation

plans & for the public’s consideration in purchasing flood insurance Corps will coordinate with local flood control agencies in

reducing the flood risk hazard

217217217

200200200

255255255

000

163163163

131132122

2396553

110135120

1129256

62102130

1025648

130120111

237237237

8011927

252174.59

“The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”

Prepared by

Rene Vermeeren, P.E., D. WRE.

Chief, Hydrology and Hydraulics Branch

PRESENTATION FOR THE POTENTIAL ADDITION OF SPECIAL FLOOD HAZARD AREAS

PART 2: LOS ANGELES COUNTY DRAINAGE AREA STUDY RESULTS

14

File Name

17 October 2016

File Name

15PRESENTATION OVERVIEW Los Angeles County Drainage Area Feasibility Study Floodplain Mapping LACDA Study Study Results

File Name

16LOS ANGELES COUNTY DRAINAGE AREA Review Feasibility Study (1992)

Source LACDA Feasibility Study (1992)

File Name

17FLOODPLAIN MAPPING

Downtown Los Angeles

Hansen Dam

Sepulveda Dam

Glendale Narrows

Los Angeles River

Source: LACDA Feasibility Study (1992)

File Name

18LACDA STUDY

Source: LACDA Feasibility Study (1992)

1992 LACDA study evaluated flooding for entire LACDA system Extended from San Gabriel Mountains to the ocean Purpose: propose modifications to reduce flood risk

The flood damage reduction general measures evaluated Reduce inflow to the system (detain water) Convey more water in the system (increase channel capacity) Damage management (floodfighting, floodproofing, etc.) Alter the reservoir’s current operating regulations

Several measures were considered as solutions to the flooding problem Deepen/Widen channels, alter channel shape Raise channel walls Modify bridges Divert flows into tunnels or detention facilities

File Name

19STUDY RESULTS

Source: LACDA Feasibility Study (1992)

Project Justification Average Annual Benefits must exceed the Average Annual Cost of

the measures considered (B/C ratio) Benefits are derived from reduction of floodplain damages when

evaluating measures.

Results of study found: Evaluation of measures indicate low benefit to cost ratio Measures not economically justified Report recommended no action for this reach