EXHIBIT_A_-_Laveen_Area_Drainage_Feasibilty_Study.pdf

LAVEEN AREA DRAINAGE

FEASIBILITY STUDY

Planning & Development Department

3/24/2022

FINAL

LAVEEN AREA DRAINAGE FEASIBILITY STUDY

Prepared for

City of Phoenix Planning & Development Department

Project No. 8591000000

March 24, 2022 (FINAL)

Prepared by

410 N. 44th Street, Suite 460 Phoenix, AZ 85008

Project No. 2010020901

In Collaboration with

8400 S Kyrene Rd, Suite 201 Tempe, AZ 85284

CITY OF PHOENIX

Planning & Development Department ii Wilson & Company, Inc.

Table of Contents List of Tables ............................................................................................................iv

List of Figures............................................................................................................v

Executive Summary..................................................................................................vi

1.0 Background

1.1 Laveen Area Description

1.2 Demographics

1.3 Study Area

1.4 Key Drainage Studies and Projects in the Area

2.0 Purpose and Need Statement

3.0 Transportation Network Assessment

4.0 Hydrologic Evaluation of Study Area

4.1 Laveen Area Drainage Master Study/Plan Update

4.2 LADFS Design Criteria

4.3 Identification of Opportunity Areas

4.4 GIS Development

4.5 Workshop #1

5.0 Development of Project Alternatives

5.1 Evaluation of Opportunity Areas

5.1.1 Opportunity Area 1

5.1.2 Opportunity Area 2

5.1.3 Opportunity Area 3

5.1.4 Opportunity Area 4

5.1.5 Opportunity Area 5

5.1.6 Opportunity Area 6

5.1.7 Opportunity Area 7

5.1.8 Opportunity Area 8

5.1.9 Opportunity Area 9

5.1.10 Opportunity Area 10

5.1.11 Opportunity Area 11

Planning & Development Department iii Wilson & Company, Inc.

5.2 Workshop #2

5.3 Final Selection of Alternatives

6.0 Actionable Project Alternatives

6.1 Project Descriptions

6.2 Schematic Level Designs and Cost Estimates

6.3 Funding Considerations

6.4 Cost/Benefit Considerations

7.0 Conclusions and Recommendations

References

Planning & Development Department iv Wilson & Company, Inc.

List of Tables

Table ES1 – Summary of Hazard Areas and Potential Mitigation Alternatives........................................vi

Table 1 - Neighborhood Level Opportunity Area (Hazard Area) and Potential Mitigation Alternatives. ..9

Table 2 - Potential Mitigation Alternatives Ranking Matrix

Table 3 - Recommended Mitigation Alternatives Summary

Table 4 - Description, Budgetary Cost, and Time Horizon for Recommended Alternatives

Table 5 - Potential Funding Sources Per Project Alternative

Table 6 - Preliminary Cost/Benefit Ratios

Table 7 - Summary of Recommended Alternatives with Potential Funding Sources and Costs

Planning & Development Department v Wilson & Company, Inc.

List of Figures Figure ES1 – Summary Map of the Opportunity Areas and Recommended Alternatives .......................ix

Figure 1 - Outline of the Laveen Village within the City of Phoenix

Figure 2 - City of Phoenix Urban Villages Map, highlighting the Laveen Village

Figure 3 – Map of the City’s Council Districts

Figure 4 - Study Area of the MAG 2020 Laveen South Mountain Transportation Study

Figure 5 - Study Area of the FCDMC 2017 Area Drainage Master Study/Plan Update

Figure 6 - Name and location of the Regional Drainage CIPs resulting from the Laveen ADMS/PU

Figure 7 - Laveen ADMS/PU Areas of Mitigation Interest, CIP solutions, and Neighborhood Level Opportunity Areas

Figure 8 - Neighborhood Opportunity Area 1 with Flood Mitigation Options

Figure 9 - Neighborhood Opportunity Area 2 with Flood Mitigation Options

Figure 10 - Neighborhood Opportunity Area 3 with Outfall Conveyance Options

Figure 11 - Neighborhood Opportunity Area 5 with Flood Mitigation Options

Figure 12 - Neighborhood Opportunity Area 6 with Flood Mitigation Options

Figure 13 - Neighborhood Opportunity Area 7 with Flood Mitigation Options

Figure 14 - Neighborhood Opportunity Area 8 with Outfall Conveyance Options

Figure 15 - Neighborhood Opportunity Area 9 with Flood Mitigation Options

Figure 16 - Neighborhood Opportunity Area 10 with Flood Mitigation Options

Figure 17 - Combined Alternative A1-O3 and A11-O2

Figure 18 - MCDOT Maintained Roads near 35th Ave and Carver Road

Planning & Development Department vi Wilson & Company, Inc.

Executive Summary The goal of the Laveen Area Drainage Feasibility Study (LADFS) was to identify smaller (i.e., 5 to 10-year level) flood mitigation alternatives that would supplement the regional flood control projects that have been or will be implemented in the Laveen Village area, a rapidly-urbanizing agricultural community of approximately 48 square miles situated southwest of downtown Phoenix. This area is part of the City of Phoenix and comprises parts of Phoenix City Council Districts 7 and 8.

The Laveen area has a long history of flooding problems, and the area has been studied extensively over the past 40 years culminating in the Laveen Area Drainage Master Study Plan Update (Laveen ADMS/PU), a 2017 study that updated the hydrology with a FLO-2D model, identified 5 areas of mitigation interest (AoMI), and recommended 5 regional alternatives to mitigate flooding. The LADFS built on this study by updating the Laveen ADMS/PU FLO-2D modeling with grading for a new subdivision and developing a 5-year storm event rainfall file. These updated results were used to identify 11 neighborhood level hazard areas (hazard areas) where smaller scale flood control projects would have a benefit.

Through collaborative meetings and workshops with the project team (both consultant and city staff), a total of 29 potential flood mitigation alternatives were developed with one hazard area (Area

4) being excluded from alternative development because flooding in this was more efficiently handled in a downstream hazard area (Area 5). The 11 hazard areas and 29 alternatives are summarized in Table 1.

These 29 alternatives were independently ranked by the project team. These individual rankings were summarized, reviewed during another meeting, and distilled down to 13 total recommended alternatives. During this process, alternative 3 for Hazard Area 1 was combined with alternative 2 in Hazard Area 11 because they share a common outfall, thereby reducing the 13 alternatives to 12.

The final 12 recommended alternatives are shaded in Table ES1 and summarized in Figure ES1.

From these 12 alternatives, 6 were chosen for a concept schematic design with a more detail concept cost estimate. Finally, funding opportunities were identified for each of the recommended alternatives and results from recently completed transportation studies to help identify opportunities for shared right-of-way or shared mobilization costs.

Table ES1 – Summary of Hazard Areas and Potential Mitigation Alternatives

Hazard Area ID Mitigation Alternatives1

1. Storm Drain down Dobbins Rd from 38th to 47th Ave to connect to new storm drain for LADMPU AoMI2.

2. Storm drain at Dobbins Village West channel terminus to new storm drain down 43rd Ave, to Dobbins Road storm drain.

3. Convert basins along west side of Dobbins Village to a channel, then storm drain down Dobbins Rd to 47th Ave.

4. Tile irrigation ditch north of Dobbins Road, west of 35th Ave to encourage more flow to enter Aguila Golf Course.

Planning & Development Department vii Wilson & Company, Inc.

Hazard Area ID Mitigation Alternatives1

1. New Culvert under Carver/35th Ave

2. Rules of Development: Increased retention requirements and enhanced single lot retention requirement

1. Extend Olney storm drain to wash around 20th Ave alignment

2. Install a new lateral down 19th Ave to connect to outfall of planned development. 19th Ave lateral would tie into planned storm drain for 19th Ave project.

4 Area Excluded – No alternatives developed

1. Extend lateral down 15th Ave to connect to existing retention basin to the east off W Buist Ave

2. Extend lateral down 15th Ave to Olney Ave, east to Police Academy parking lot

1. Extend existing laterals at Chambers St and Sunland Ave to 38th Dr

2. Retention basin(s) at Maurice C Cash Elementary school fields north of Grove St

3. Basin at Playa Margarita Park (off Roeser Rd)

4. Discharge new storm drains to existing gravel pit west of 39th Ave.

5. Extend storm drain down Huntington Dr

1. Add laterals and catch basins to 27th Ave storm drain at Dobbins Road.

2. Construct new storm drain from east of 27th Ave and discharge to new Culverts (AoMI 3) to Aguila Golf Course

1. Storm drain laterals off 19th Ave down Wier, Corona, Tamarisk.

2. Increase capacity of existing 19th Ave storm drain north of Broadway if it would increase capacity of system to the south and along Broadway Road.8

3. Storm drain reliever off 19th Ave storm drain to Lindo Park. Extend lateral south off Broadway on 17th Ave.

Planning & Development Department viii Wilson & Company, Inc.

Hazard Area ID Mitigation Alternatives1

1. Storm drain beginning at new Culverts (AoMI2) at Aguila Golf Course down 35th Ave, then down Carver Road (Telegraph Pass Canal)

2. 35th Ave storm drain from Dobbins Road to Olney, down Olney to 32nd Dr, to Carver Road along the Western Canal

3. Channel along Telegraph Pass Canal to basin. Channel outlet from basin to storm drain that then outlets to Dobbins Place channel (assumes culverts under Dobbins are in place).

4. Channel along Olney that outlets to Dobbins Place channel (assumes culverts under Dobbins are in place).

5. Channel along Olney to Basin. Basin outlets to storm drain that runs north along 35th Ave and outlets to Dobbins Place channel (assumes culverts under Dobbins are in place).

10 1. Storm drain down 27th Ave, then down Sunrise Dr

1. Increase channel capacity west of 44th Ln

2. 43rd Ave storm drain to Sunrise Dr, east to 39th Ave (This alternative was combined with Hazard Area 1 – Option 3).11

3. Alternatively, take storm drain down Olney for ADMPU AoMI 2 storm drain.

1Recommended alternatives are shown with shading

Planning & Development Department ix Wilson & Company, Inc.

Figure ES1 – Summary Map of the Opportunity Areas and Recommended Alternatives

Planning & Development Department 1 Wilson & Company, Inc.

1.0 Background

1.1 Laveen Area Description

The city’s Laveen Village is a rapidly-urbanizing agricultural community of approximately 48 square miles situated southwest of downtown Phoenix, between South Mountain Park & Preserve western ridges to the south, the Salt River to the north, the Gila River Indian Reservation to the west and S.

27th Avenue to the east. The new Loop 202 South Mountain Freeway spans along its southwest boundary then extends north roughly along 59th Avenue. Figure 1 outlines Laveen Village per above. Land in gray color is incorporated, whereas that in beige color is unincorporated.

Figure 1 - Outline of the Laveen Village within the City of Phoenix.

Planning & Development Department 2 Wilson & Company, Inc.

Figure 2 shows the location of the Laveen Village within the City of Phoenix boundaries. About 25 percent of Laveen is currently unincorporated (Maricopa County). Per Figure 3, portions of Laveen Village are in Council District 7 and Council District 8.

Figure 2 - City of Phoenix Urban Villages Map, highlighting the Laveen Village.

Figure 3 – Map of the City’s Council Districts.

Planning & Development Department 3 Wilson & Company, Inc.

1.2 Demographics

There are roughly 48,000 residents in Laveen, with a median age of about 31 years. Of this population, about 49% are males and 51% are females. US-born citizens make up for nearly 83% of the resident pool in Laveen, while roughly 7% of the population is represented by non-citizens.

White-collar workers make up 78% of the working population in Laveen, while blue-collar employees account for the remaining 22%. The average annual household income in Laveen is approximately $89,000, while the median household income sits at about $76,000 per year.

There are nearly 13,330 households in Laveen, each made up of around 4 members. Of these, about 73% are owner-occupied, with the remainder in rented dwellings. Properties bought with mortgages account for roughly 80% of the units, and the median value of a home with a mortgage is $240,000.

Family establishments represent about 81% of these Laveen households. Additionally, about 53% of households have children.

The top three means of transportation people in Laveen use to get to work are: car, public transit, and walking; with nearly 42% of the population commuting by car.

Source: U.S. Census Bureau, the 2019 American Community Survey, provided by Point2Homes.com

1.3 Study Area

The general study area is the Laveen Village, but it uses results of two previous studies which used slightly different study boundaries. The first is the Maricopa Association of Governments (MAG) 2020 Laveen South Mountain Transportation Study. The study area is shown in Figure 4, which is missing the southernmost region of Laveen Village. The study and its recommended roadway infrastructure improvements served as the foundation for supplemental analysis to identify complementary zonal drainage improvement strategies.

Figure 4 - Study Area of the MAG 2020 Laveen South Mountain Transportation Study

The second study was the Flood Control District of Maricopa County (FCDMC) 2017 Laveen Area Drainage Master Study/Plan Update (ADMS/PU). The study included analysis of existing regional

Planning & Development Department 4 Wilson & Company, Inc.

drainage improvements such as detention basins, channels, storm drains and culverts, much of which has been constructed based on recommendations from earlier versions of the regional drainage master plans. The corresponding study area is shown in Figure 5, which includes more runoff area than Laveen Village alone. Essentially, the land area east of 27th Avenue is outside of the Laveen Village.

Figure 5 - Study Area of the FCDMC 2017 Area Drainage Master Study/Plan Update

1.4 Key Drainage Studies and Projects in the Area

The South Phoenix / Laveen area has been studied extensively over the past 40 years, and a significant number of flood control projects have been implemented over that time. Some selected studies that document the results of the analyses and proposed flood control solutions are:

• Cellar Barr Associates, Revised November 1991, Laveen Area Master Drainage Study.

• HDR, January 1997, South Phoenix/Laveen Drainage Improvement Project – Project

Summary Report.

• HDR, November 2001, Laveen Area Drainage Master Plan.

• Stanley Consultants, May 2013, South Phoenix/Laveen Drainage improvement Project

Addendum Final Report.

• Stanley Consultants, May 2013, South Phoenix Two Basins Project Final Design Report.

• Stantec Consulting, June 2015, Laveen ADMP Update Report.

Exhibits showing the study area and the projects resulting from some of the above studies are presented in Appendix A.

Planning & Development Department 5 Wilson & Company, Inc.

After the major storms of 2014, which highlighted the major flooding issues that still exist in the area, the FCDMC commissioned studies (e.g., the 2015 Stantec Study) to reevaluate the ADMP for this area and recommend updates to the original 2001 plan.

Finally, the 2017 Laveen ADMS/PU was initiated to restudy the entire area using a 2D model developed with FLO-2D and to update the plan based on the results of the 2D analysis. A total of 5 regional flood control projects in the Laveen watershed (refer to Figure 6 for general location) were defined in the 2017 Laveen Area Drainage Master Study/Plan Update (ADMS/PU). These are:

1. Hidden Valley: Consisted of two regional basins, one northwest of Carver Road and 43rd about 4.5 acres in size and, the other, east of 43rd near Sunset Cove about 5 acres in size. In addition, the construction of a storm drain along Estrella Drive to drain the new regional basins west to outfall in the drainage system for the SR202 Freeway.

2. 51st Avenue and Sunrise Drive: Consisted of a new basin approximately 6 acres in size at the southeast corner of 51st and Sunrise with collector channels and a 36-inch diameter storm drain to discharge flow from the new basin to the offsite drainage system for the SR202 Freeway. Also, addition of catch-basin inlets and laterals along 51st between the new basin and Olney Avenue, plus the construction a 42-inch diameter storm drain along 47th from Olney to Dobbins Road and a 48- inch diameter storm drain west in Dobbins from 47th to an existing 72-inch diameter storm drain in 51st, along with catch-basin inlets.

3. 35th Avenue and Dobbins Road: Consisted of a four-barrel, 48-inch diameter culvert under the intersection at Dobbins and 35th to drain flow from the existing subdivision channel into regional detention storage basins previously constructed in the Aguila Golf Course. Additionally, the construction of a storm drain with future Dobbins Road widening project that would improve roadway and intersection drainage. The storm drain would also outfall to Aguila Golf Course.

4. 27th Avenue and Olney Avenue: Consisted of a 72-inch diameter storm drain in Olney from about 24th Avenue west to 27th Avenue, then north to the existing 27th and South Mountain Avenue regional basin. This storm drain would have large inlets at multiple locations on Olney to intercept drainage, as well as multiple inlets along 27th, including a large inlet for the subdivision retention basin just south of the Western Canal. It also included the construction of Hazard Mitigation Assistance (HMA) regional retention basins on about 4.5 acres along 23rd Avenue north of Olney.

5. 19th Avenue and Dobbins Road: Consisted of a regional detention basin on about 5.5 acres at the northeast corner of 15th Avenue and Dobbins, including a 4-barrel, 54-inch diameter basin inlet culvert under Dobbins to intercept flow from the existing Humane Society channel. In addition, the construction of a storm drain in Dobbins from the new regional basin west to 19th, then north to South Mountain Avenue, then west to the existing 27th and South Mountain Avenues regional basin. The storm drain would range in size from 54-inch diameter along Dobbins Road to 72-inch diameter along South Mountain Avenue.

The storm drain would have large inlets along Dobbins and numerous smaller inlets along 19th and South Mountain Avenues.

Planning & Development Department 6 Wilson & Company, Inc.

Figure 6 - Name and location of the Regional Drainage CIPs resulting from the Laveen ADMS/PU.

2.0 Purpose and Need Statement

The Laveen Village has seen considerable development in the last decade, much stimulated by the construction of the Loop 202 South Mountain Freeway. Inevitably, development accentuates the need for proper drainage planning and effective infrastructure to avoid flooding. The Laveen area received heightened focus regarding drainage due to the wide-spread flooding resulting from the 2014 Monsoon storms.

The City of Phoenix seeks to supplement the regional flood control projects set to be designed and constructed by the Flood Control District of Maricopa County (in partnership and cost-sharing with the City) within the Laveen watershed in South Phoenix. These zonal solutions sought by this study are meant to be smaller in scale (designed to a 5- to 10-year storm event) than the 2017-planned regional solutions, and potentially funded by impact fees. This study was identified as the Laveen Area Drainage Feasibility Study (or LADFS hereafter).

3.0 Transportation Network Assessment

Two separate transportation-led studies were leveraged for this drainage feasibility study. First, the 2017 Dobbins Road Design Concept Report (DCR) Update, which was an update to the earlier Dobbins Road DCR that was originally completed in 2003. The Dobbins Road DCR Update was completed due to the considerable development in the area and a heightened focus on drainage due

Planning & Development Department 7 Wilson & Company, Inc.

to the flooding from the 2014 Monsoon storms. The Dobbins Road DCR Update included an analysis of existing conditions, roadway section traffic volume, zoning, and right-of-way requirements. It also examined the drainage and flooding along the corridor and provided an analysis of the effects of placing portions of the Western and Highline Canals underground as pipes.

A comprehensive analysis of the study area transportation network was also recently conducted in conjunction with the 2020 Laveen South Mountain Transportation Study, prepared for Maricopa Association of Governments (MAG). The study utilized the MAG travel demand model to forecast future travel demands for future years 2030, 2035, and 2040. These travel demands, in combination with historical crash data and public and stakeholder input, were used to develop recommendation for the timing of roadway, intersection, bicycle, pedestrian, and transit improvements in the study area for years 2030, 2035, and 2040. Recommendations from this study, provided in Appendix B.

The recommended cross sections were used to evaluate the ultimate right-of-way needs for the resulting improvements to corridors within the study area. The calculated right-of-way requirements were then compared to existing available right-of-way, based on right-of-way information collected during conduct of the Laveen South Mountain Transportation Study. A table summarizing this comparison is provided in Appendix C.

This comparison enabled identification of roadway segments which may require additional right-of-way to accommodate proposed improvements, as well as segments where additional right-of-way may be available, beyond the future right-of-way requirements. For those segments with excess available right-of-way, opportunities may exist to incorporate future drainage infrastructure improvements without requiring purchase of additional right-of-way.

4.0 Hydrologic Evaluation of Study Area

4.1 Laveen Area Drainage Master Study/Plan

Update The Laveen Area Drainage Master Study/Plan Update1 (ADMS/PU) was completed in 2017 and included the development of new, detailed hydrologic & hydraulic modeling for the study area. The ADMS/PU study team also identified 5 regional Areas of Mitigation Interest (AoMIs) and proceeded through an alternatives analysis that resulted in a recommended flood mitigation Capital Improvement Project (CIP) for each AoMI. Schematic design and analysis were conducted for each CIP during the ADMS/PU. The design storm recommended for each CIP is either the 10-year or 100-year recurrence interval. The FCDMC has completed final design for one of the CIPs (27th Ave Storm Drain) and final design is currently underway for another (19th Ave and Dobbins Storm Drain). Two of the remaining three CIPs are programmed for final design to begin in 2022.

1 JE Fuller, Laveen Area Drainage Master Study/Plan Update Summary Report and Recommended Plan, December 2017.

Planning & Development Department 8 Wilson & Company, Inc.

The LADFS Team (comprised of City staff and consultants) agreed that it should be assumed that all the ADMS/PU CIPs are in place for the purposes of identifying neighborhood level Opportunity Area solutions. The CIPs will provide a logical outfall for potential flood mitigation solutions.

4.2 LADFS Design Criteria

The LADFS Team agreed that neighborhood level Opportunity Area solutions will be sized for higher frequency storm events in the range of the 5- to 10-year storm flow rates. The team acknowledged that in some areas, existing buildings are not susceptible to flooding from these smaller storm water events. However, infrastructure sized for these higher frequency events will still benefit existing and proposed improvements in the lower frequency (i.e., larger) events (e.g., a 100-year storm event).

4.3 Identification of Opportunity Areas

The results from the Laveen ADMS/PU study were used to identify neighborhood level Opportunity Areas. These included the 10-year and 100-year FLO-2D flow depth and discharge gridded data along with the results of a building inundation analysis. The inundation analysis identified buildings that were susceptible to flooding of more than 0.5-feet for the 10-year and 100-year flood events. Furthermore, drainage complaints and Opportunity Areas that were identified prior to the ADMS/PU were reviewed but did not provide much insight given the fact that it is not a comprehensive database.

Opportunity Areas identified included developed land with multiple affected properties, undeveloped land with significant offsite drainage, or a combination of the two. A total of 11 neighborhood level Opportunity Areas were identified after reviewing the results. The 11 Opportunity Areas are shown in Figure 7 along with the 5 AoMIs identified during the Laveen

ADMS/PU.

4.4 GIS Development

Much of the LADF study GIS data was obtained from the Laveen ADMS/PU. Existing storm water infrastructure and CIP schematic alignments were used to identify opportunities for neighborhood level Opportunity Area solutions. Existing and proposed ADMS/PU CIPs are shown on Figure 7.

4.5 Workshop #1

The LADFS Team on June 29, 2021, for a workshop to review the neighborhood level Opportunity Areas identified and conceptual level alternatives. Staff was in general agreement with the Opportunity Areas and conceptual level alternatives listed in Table 1. The city staff recommended that additional information be provided for each alternative, including potential funding opportunities, high level construction cost estimates, qualitative benefit/cost assessment, and recommendations for prioritization or rank of each alternative/Opportunity Area. This was conducted after Workshop #1 and is shown in Table 1.

Planning & Development Department 9 Wilson & Company, Inc.

Table 1 - Neighborhood Level Opportunity Area (Hazard Area) and Potential Mitigation Alternatives.

Planning & Development Department 10 Wilson & Company, Inc.

Figure 7 - Laveen ADMS/PU Areas of Mitigation Interest, CIP solutions, and Neighborhood Level Opportunity Areas

Planning & Development Department 11 Wilson & Company, Inc.

5.0 Development of Project Alternatives

The concept level project alternatives discussed during Workshop #1 were advanced further to conduct a more detailed evaluation as described in the following sections.

5.1 Evaluation of Opportunity Areas

The potential alternatives for each Opportunity Area were refined using the GIS data collected and described previously. Schematic locations and alignments of storm drains, conveyance channels, and basins were refined to identify opportunities and constraints.

5.1.1 Opportunity Area 1

Neighborhood level Opportunity Area 1 (Hazard ID 1) is an area approximately the quarter section on the southeast corner of 43rd Ave and Dobbins Rd. The area includes the Dobbins Village subdivision currently under construction, a planned development adjacent and to the east, and the Laveen Elementary School. Dobbins Village and the planned development would have benefited from a stormwater outfall along Dobbins Road, but since one doesn’t exist, both developments include a “pass through” conveyance system for offsite flows from Carver Mountain.

Mitigation solutions outlined in Table 1 were developed to provide a comprehensive outfall for flows exiting Dobbins Village at the southeastern corner of the Laveen Elementary School. The schematic alternatives (options) are shown in Figure 8. It should be noted that Opportunity Area 11 options are also shown in Figure 8, this will be discussed later.

Planning & Development Department 12 Wilson & Company, Inc.

Figure 8 - Neighborhood Opportunity Area 1 with Flood Mitigation Options

5.1.2 Opportunity Area 2

Neighborhood level Opportunity Area 2 (Hazard ID 2) is an area of approximately 250 acres of which, about 80% is private land and undeveloped in the vicinity of 35th Ave & Carver Rd. There are two primary concerns with this area including an undersized cross drainage culvert at the complex intersection of 35th Ave, Carver Rd, and Ceton Dr; and existing and undeveloped private land that receive offsite flows from areas upstream including Carver Mountain.

Mitigation solutions outlined in Table 1 were developed to address the road cross drainage structure and to mitigate storm water for the area. The schematic alternatives (options) are shown in Figure 9.

Planning & Development Department 13 Wilson & Company, Inc.

Figure 9 - Neighborhood Opportunity Area 2 with Flood Mitigation Options

5.1.3 Opportunity Area 3

Neighborhood level Opportunity Area 3 is an area southwest of 19th Ave and Dobbins Rd with several proposed subdivisions in various stages of development. The area has significant offsite drainage from South Mountain runoff and no controlled outfall location.

Mitigation solutions outlined in Table 1 were developed primarily to identify outfall locations and conveyance alternatives for the area. The schematic alternatives (options) are shown in Figure 10.

Planning & Development Department 14 Wilson & Company, Inc.

Figure 10 - Neighborhood Opportunity Area 3 with Outfall Conveyance Options

5.1.4 Opportunity Area 4

Opportunity Area 4 was identified to mitigate the long duration outflow from the Mineral Canyon Detention Basin. The area shown in Figure 7 was identified to capture a previously identified alternative evaluated and abandoned during the Laveen ADMS/PU. The alternative consisted of a storm drain along 7th St beginning south of McNeil St to Baseline Rd over a mile in length. The LADF Study team identified another alternative within neighborhood level Opportunity Area 5 that would address the long duration outflow that will be discussed in the next section. Therefore, Opportunity Area 4 was removed from the focus of this study.

5.1.5 Opportunity Area 5

Opportunity Area 5 results from significant runoff generated from South Mountain and the Mineral Canyon Detention Basin outflows. The area is generally located along 15th Ave between Olney Ave and Dobbins Rd. The primary drainage problems include offsite flows through the Mountain Gate mobile home park, flooding along 15th Ave, and flooding of the Humane Society.

Mitigation solutions outlined in Table 1 were developed to provide a comprehensive conveyance system for South Mountain runoff concentrated through the Police Academy campus and outflows from the Mineral Canyon Detention Basin. The schematic alternatives (options) are shown in Figure 11.

Planning & Development Department 15 Wilson & Company, Inc.

Figure 11 - Neighborhood Opportunity Area 5 with Flood Mitigation Options

5.1.6 Opportunity Area 6

Opportunity Area 6 is an existing subdivision (Independence Park) northeast of 39th Ave and Southern Rd. Part of the subdivision receives runoff from unmitigated neighborhood drainage north of Roeser Rd that crosses through the Playa Margarita Park and through a Maurice C. Cash Elementary School field.

Mitigation solutions outlined in Table 1 were developed to improve drainage through the Independence Park subdivision or to eliminate or reduce flows entering the subdivision. The schematic alternatives (options) are shown in Figure 12.

Planning & Development Department 16 Wilson & Company, Inc.

Figure 12 - Neighborhood Opportunity Area 6 with Flood Mitigation Options

5.1.7 Opportunity Area 7

Opportunity Area 7 primarily consists of existing rural residential and agricultural developments northwest of 27th Ave and Dobbins Rd with most properties within unincorporated Maricopa County. The inundation analysis conducted during the Laveen ADMS/PU identified multiple residential structures that are susceptible to flooding during a 10- or 100-year runoff event.

Mitigation solutions outlined in Table 1 were developed to intercept flows crossing Dobbins Rd east of the 27th Ave intersection. The schematic alternatives (options) are shown in Figure 13.

Planning & Development Department 17 Wilson & Company, Inc.

Figure 13 - Neighborhood Opportunity Area 7 with Flood Mitigation Options

5.1.8 Opportunity Area 8

Opportunity Area 8 primarily consists of an existing residential development that was built in the 1950s and a portion of 19th Avenue that stretches from Broadway Road to the north and Southern Avenue to the south within the City of Phoenix. The inundation analysis conducted during the Laveen ADMS/PU identified multiple residential structures that are susceptible to flooding during a 10- or 100-year runoff event. Additionally, the storm drain capacity analysis performed during the Laveen ADMS/PU indicated that the 19th Avenue storm drain was overtaxed and multiple inlets along 19th Avenue would flood during a 100-year event.

Mitigation solutions outlined in Table 1 were developed to relieve pressure on the 19th Avenue storm drain drainage through larger downstream pipes or a reliever pipe that drains to the Lindo Park basin. Laterals and inlets were added within the residential to alleviate some flooding within the neighborhood. The schematic alternatives (options) are shown in Figure 14.

Planning & Development Department 18 Wilson & Company, Inc.

Figure 14 - Neighborhood Opportunity Area 8 with Flood Mitigation Options

5.1.9 Opportunity Area 9

Opportunity Area 9 is an area that is roughly bounded by Dobbins Rd to the north, 35th Ave to the west, 31st Ave to the east, and the Telegraph Pass Canal to the south with a portion of the Opportunity Area extending past 35th Ave for approximately 1000 feet. The area includes two subdivisions, Dobbins Place and Dobbins Corner, that are within the City of Phoenix, but the rest of the area is unincorporated Maricopa County. The major floodwaters originate from the mountains to the south, overtop the Telegraph Pass Canal, and flow through single lot development or agricultural fields until they reach the drainage channel of Dobbins Place.

Mitigation solutions outlined in Table 1 were developed to capture and contain the flow from mountain front to the existing downstream drainage infrastructure. The schematic alternatives (options) are shown in Figure 15.

Planning & Development Department 19 Wilson & Company, Inc.

Figure 15 - Neighborhood Opportunity Area 9 with Flood Mitigation Options

5.1.10 Opportunity Area 10

Opportunity Area 10 is an area south of Olney Ave, north of Sunrise Dr, and east of 27th Ave. The major floodwaters originate from the mountains to the south and flow through large rural lots. The 27th Ave and Olney Ave FCDMC CIP is expected to go into construction in 2022. The proposed storm drain in Olney Ave will collect some of the flows through Opportunity Area 10 but will not benefit this upstream area.

The mitigation solution outlined in Table 1 was developed to collect the flow from mountain front and convey it to the proposed 27th Ave storm drain. The schematic option is shown in Figure 16.

5.1.11 Opportunity Area 11

Neighborhood level Opportunity Area 11 contains large, rural lots that receive runoff from Carver Mountain to the south in an uncontrolled fashion. The area is south of Sunrise Dr and east of 43rd Ave. Opportunity Area 11 was combined with Opportunity Area 1 as discussed previously. The schematic alternatives (options) are shown in Figure 8. It should be noted that Opportunity Area 1 options are also shown in Figure 8.

Planning & Development Department 20 Wilson & Company, Inc.

Figure 16 - Neighborhood Opportunity Area 10 with Flood Mitigation Option

5.2 Workshop #2

The LADFS Team met again on July 29, 2021, for a second workshop to review the conceptual alternatives (options) to mitigate neighborhood level Opportunity Areas. City staff felt more information was needed to evaluate the alternatives including benefited area land use, number of buildings benefited, right-of-way acquisition, etc. Therefore, the LADFS consultants developed a matrix that included the additional information along with a ranking for each, individual study team member to complete. Furthermore, a web-based GIS database hosting base map information and the Options for each Opportunity Area was developed and provided to City Staff for review.

The LADFS Team met again on August 18, 2022, to jointly review the matrix. Revisions were made to the matrix and then it was distributed to each LADFS Team member for individual rankings.

The individual rankings were composited or averaged to assist with determining the most feasible option. The final matrix and rankings are shown in Table 2.

Planning & Development Department 21 Wilson & Company, Inc.

Table 2 - Potential Mitigation Alternatives Ranking Matrix

Planning & Development Department 22 Wilson & Company, Inc.

5.3 Final Selection of Alternatives

The LADFS Team met again September 20, 2021, and October 6, 2021, to review the compiled ranking matrix shown in Table 2. City Staff suggested a final summary table be developed which includes possible grant or funding sources and to establish a time frame for the implementation of each alternative. The alternative summary is shown in Table 3.

Table 3 - Recommended Mitigation Alternatives Summary

Each alternative listed in Table 3 is recommended for further evaluation and design (not a part of this Study). It was determined that 6 of the 11 alternatives would be advanced to a more detailed schematic design and project cost estimate as shown in Table 3. The City reviewed the schematic design plans and provided comments during a LADFS Team meeting held on January 27, 2022.

Hazard Area ID

Mitigation Alternatives (Options) ROM Cost Time

Horizon Schematic

Design

3. Convert basins along west side of Dobbins Village to a channel, then storm drain down Dobbins Rd to 47th Ave.

$1,300,000 5-year 1Yes

4. Tile irrigation ditch north of Dobbins Road, west of 35th Ave to encourage more flow to enter Aguila Golf Course.

$900,000 Near term No

1. New Culvert under Carver/35th Ave $120,000 Near term No

2. Rules of Development: Increased retention requirements and enhanced single lot retention requirement

$0 Near term No

2. New lateral down 19th Ave from planned regional storm drain project to connect to outfall of planned development.

$240,000 5-year Yes

2. Extend lateral down 15th Ave to Olney Ave, east to Police Academy Parking Lot

$1,900,000 10-year Yes

6 3. Basin at Playa Margarita Park (off Roeser Rd) $140,000 Near term Yes

1. Add laterals and catch basins to 27th Ave Storm Drain at Dobbins Road.

$150,000 Near term No

3. Storm drain reliever off of 19th Ave Storm Drain to Lindo Park. Extend lateral south off of Broadway on 17th Ave.

$800,000 10-year Yes

4. Channel along Olney that outlets to Dobbins Place Channel (assumes culverts under Dobbins are in place).

$900,000 10-year Yes

10 1. Storm drain down 27th Ave, then down Sunrise Dr $1,000,000 10-year No

1. Increase channel capacity west of 44th Ln $200,000 Near term No

2. 43rd Ave storm drain to Sunrise Drive, east to 39th Ave $4,700,000 5-year 1Yes

1 Combine problem area 1, option 3 with problem area 11, option 2 for Schematic Design

Planning & Development Department 23 Wilson & Company, Inc.

6.0 Actionable Project Alternatives

6.1 Project Descriptions

Project descriptions, a budgetary cost, and a time horizon for implementation have been developed for all recommended alternatives and are summarized in Table 4 (next page).

As shown in Table 4, seven alternatives were chosen to have a concept design developed. This number was reduced to six because alternatives A1-O3 and A11-O2 were combined into one overall design since both alternatives included an outfall north on 43rd Ave (see Figure 17). For the combined A1-O3 and A11-O2 alternative, the outfall was combined into one outfall – the improved channel at the western edge of the Laveen Elementary School and the Dobbins Village subdivision.

Figure 17 - Combined Alternative A1-O3 and A11-O2

6.2 Schematic Level Designs and Cost Estimates

Schematic designs were developed for the six alternatives and are presented in Appendix D. In addition, concept cost estimates (e.g., a 15% planning level) were developed and are itemized in Appendix E.

Planning & Development Department 24 Wilson & Company, Inc.

Table 4 - Description, Budgetary Cost, and Time Horizon for Recommended Alternatives

Hazard Area ID

Project Alternative

ID

Proposed Project Alternative Name Alternative Project Description1 Budgetary

Cost

A1 - O3 43rd Ave Conveyance Improvements (combined with A11-O2)

A 48-inch storm drain will start at an inlet catch basin located at Sunrise Dr. and 40th Ave., the storm drain extending west along Sunrise Dr. to 43rd Ave. From the intersection of Sunrise Dr. and 43rd Ave., the storm drain will run north on 43rd Ave. to McNeil St. The storm drain will connect into an existing catch basin that is part of Lennar at Dobbins Village. A 48-inch storm drain will start again at the end of the catch basin and run north to Dobbins, then west to 47th Ave. where it will tie into regional 51st Ave & Sunrise Ave project . It will require row/easement acquisition to connect from the Lennar catch basins to Dobbins Rd.

$5,450,000

A1 - O4 Tile SRP Irrigation Ditch Tile irrigation ditch north of Dobbins Road, west of 35th Ave to encourage more flow to enter Aguila Golf Course.

$980,000

A2 - O1 Carver Rd & 35th Ave Culvert

New culvert under intersection of 35th Ave, Carver Rd, Ceton Dr, and SRP Irrigation Ditch to provide all weather access.

$540,000

A2 - O2 Increased Retention Requirements

Rules of Development: Increased Retention Requirements and Enhanced Single Lot retention requirement for udeveloped area east of 35th Ave and South of Ceton Dr.

N/A

3 A3 - O2 19th Ave Lateral

A 48-inch storm drain lateral will start from a yet vacant, undeveloped private parcel located west of 19th Ave., just southth of the western canal. The storm drain lateral will run north on 19th Ave. to Dobbins Rd., where it will connect into the 19th Ave. & Dobbins storm drain system currently under design.

$1,215,000

5 A5 - O2 15th Ave Conveyance Improvements

A 48-inch storm drain starts at an inlet structure in the catch basin of the Phoenix Regional Police Academy property and extend west on Olney Rd. to 15th Ave.

The 48-inch storm drain will continue to run north along 15th Ave. to connect to the storm drain currently being designed – the 19th Ave. and Dobbins’ storm drain system. The system transects along public row and city property.

$3,730,000

6 A6 - O3 Playa Margarita Park Basins

Construct two drainage basins in and near the playa Margarita Park located south of Roeser Rd., west of 35th Ave. Both basins will have a number of dry wells to facilitate/assist with the management of the drainage flows into the basin. The proposed basins are on city-owned property. Scuppers will be place alon the north side of the basins.

$1,176,000

7 A7 - O1 Catch Basins at 27th Ave and Dobbins Rd

Add laterals and CBs to the proposed 27th Ave Storm Drain at Dobbins Road to take advantage of proposed new storm drain under design.

$850,000

8 A8 - O3 Lindo Park Storm Drain Connection

Consists of a 24-inch reliever storm drain lateral that extends along 17th Ave.

from Chipman Rd. to an existing storm drain lateral at Tamarisk St. and discharges into an existing storm drain located further north along Broadway Rd.

In addition, the project includes a 24-inch lateral connecting Lindo Park to the existing storm drain on 19th Ave. via Roeser Rd. Both proposed storm drain laterals will be in cop row and under roadway. The plan is to add catch basins to help alleviate 19th Ave.

$1,529,000

9 A9 - O4 35th Ave & Olney Conveyance Improvements

A 75-inch bottom width earthen channel starts at the corner of 31st Dr. and Olney Ave., and extends west along the south edge of Olney Ave. At 32nd Ave., the channel crosses to the north edge of Olney Ave. and continues west to 35th Ave. At 35th Ave., the channel will continue extending north along the east side of 35th Ave. At Elliot Rd., the channel ties to a storm drain that continues to extend north to discharge into the existing basin of Dobbins Place Community Park, which extends all the way to Dobbins Rd. Drainage from the basin is discharged into the Aguila golf course via a culvert under Dobbins Rd.

$719,000

10 A10 - O1 27th Ave and Sunrise Dr Storm Drain

Connect new storm drain to proposed 27th Ave storm drain at Olney Ave. The new storm drain would be extended south along 27th Ave then east along Sunrise Dr. Catch basins will be installed to capture runoff heading north and inundating properties north of Sunrise Dr.

$1,200,000

A11 - O1 44th Ln Channel Improvements

Increase channel capacity west of 44th Ln within the Vaquero Estates subdivision $350,000

A11 - O2 43rd Ave Conveyance Improvements (combined with A1-O3)

(refer to description above) $5,449,059

1 Projects that underwent schematic design are shown with shading.

Planning & Development Department 25 Wilson & Company, Inc.

6.3 Funding Considerations

Since some projects have significant cost (e.g., combined A1-O3 and A11-O1 is estimated at a cost greater than $5 million), various funding opportunities were explored. These preliminary opportunities are summarized in Table 5 and discussed in more detail below.

Table 5 - Potential Funding Sources Per Project Alternative

For Hazard Area 1, both recommended alternatives include a significant length of improvements within the Dobbins Road corridor. Since this roadway will eventually be expanded to an arterial scenic drive2 with four lanes between 35th and 51st Avenues, there is an opportunity to include tiling (i.e., piping) of the irrigation ditch (A1-O4) and the 36-in diameter storm drain (a part of A1-O3) as a part of the roadway project. It could also have FCDMC funds, either FPAP or CIP. Additionally, the tiling of the irrigation ditch may qualify for use of SRP aesthetics funds, which is a partnership program with local municipalities that offers the opportunity to have aesthetic improvements made to existing and new SRP water and power distribution, transmission, and substation facilities. Some examples of qualify uses are:

2 Matrix, Laveen South Mountain Transportation Study for Maricopa Association of Governments, December 2020

Hazard Area ID

Project Alternative ID

Proposed Project Alternative Name Potential Funding Opportunities

A1 - O3 43rd Ave Conveyance Improvements (combined with A11-O2 below)

Combine with Dobbins Road Improvements

A1 - O4 Tile SRP Irrigation Ditch Combine with Dobbins Road Improvements / SRP Aesthetic Funds

A2 - O1 Carver Rd & 35th Ave Culvert Drainage Impact Fee / MCDOT Cost Share

A2 - O2 Increased Retention Requirements N/A

3 A3 - O2 19th Ave Lateral Drainage Impact Fee

5 A5 - O2 15th Ave Conveyance Improvements BRIC Grant, FCDMC SPAP

6 A6 - O3 Playa Margarita Park Basins Possible cost share with Parks Department and/or School District

7 A7 - O1 Catch Basins at 27th Ave and Dobbins Rd Combine with Dobbins Road Improvements, FCDMC SPAP

8 A8 - O3 Lindo Park Storm Drain Connection BRIC Grant, FCDMC SPAP

9 A9 - O4 35th Ave & Olney Conveyance Improvements

FCDMC Capital Project, SPAP, Combine with 35th Ave Road Improvements

10 A10 - O1 27th Ave and Sunrise Dr Storm Drain FCDMC SPAP

A11 - O1 44th Ln Channel Improvements Coordination with HOA

A11 - O2 43rd Ave Conveyance Improvements (combined with A1-O3 above)

Combine with Dobbins Road Improvements

Planning & Development Department 26 Wilson & Company, Inc.

Undergrounding 12KV/69KV Replacing wood poles with steel poles Installing walls, landscaping, sidewalk, and driveway improvements to substations Upgrading SRP water canals and well sites

In Hazard Area 2, both alternatives are localized in nature. Alternative A2-O1 is a culvert under 35th Ave/Carver Road. Currently, this culvert is already included in the impact fees program3.

Alternatively, a cost share with MCDOT may be possible since this culvert is on a section of where roadway maintenance responsibilities are disjointed (MCDOT maintains the entire section of 35th Ave north of Carver to approximately Olney Ave but only the right side of Carver Rd to the west of 35th Ave, see Figure 18).

Alternative A2-O2 does not require any construction costs but can be implemented through enhanced rules of development that allow for increased retention requirements.

Figure 18 - MCDOT Maintained Roads near 35th Ave and Carver Rd

For Hazard Area 3, alternative A3-O2 is dependent on the upstream development designing their infrastructure to outlet to the proposed storm drain in 19th Ave. As such, this alternative can be

3 JE Fuller, Estrella and Laveen Drainage Structure Cost Analysis, December 2018

Planning & Development Department 27 Wilson & Company, Inc.

implemented by drainage impact fees. Additionally, the 19th Ave and Dobbins R Regional Storm Drain Project4 currently includes a stub out at 19th Ave in preparation for this future storm drain.

For Hazard Area 5, the storm drain extension along 15th and Olney Avenues protects locations in the Police Academy and the Mountain Gate RV Park. Since the RV Park may have demographic values that are below the national median values and the Police Academy is a City facility critical to public safety, this project may qualify for a Building Resilient Infrastructure and Communities5 (BRIC) federal grant. However, the time frame from submitting a grant application receiving approval, finally receiving federal funding can easily stretch into years. Additionally, this federal grant application also requires a specific benefit/cost analysis using the approved FEMA mythologies that are incorporated through an Excel Add-in6. This benefit/cost analysis was outside the scope of this study since it requires detailed input parameters, such as post-improvements water surface elevations, that were not calculated. Another possible funding source would the FCDMC’s Small Project Assistance Program7 (SPAP). The SPAP allows for more rapid implementation of flood control projects, but scoring is heavily weighted for documented instances of flooding. At the time of this study, only two drainage complaints were listed in the benefited area, but this database may not be complete. Finally, as in the previous Hazard area, the 19th Ave and Dobbins Rd Regional Storm Drain Project currently includes a stub out at 15th Ave in preparation for this future storm drain extension.

Hazard Area 6 has one recommended alternative that includes basins in the open field of Maurice C Cash Elementary School and the softball field at Playa Margarita Park.