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Westpark Stormwater Bypass Reconstruction ProjectStakeholder Working Group Meeting # 2
April 3, 2019
Project Purpose
To identify, design, and construct an infrastructure project that will disconnect the existing stormwater overflow to the south pond while not causing or worsening flooding in the Westpark Subdivision.
System Overview
Project Schedule
Current Project Schedule
Project Kickoff: Oct 2018 (completed)
Data Collection: Oct ‐Nov 2018 (completed)
Pipe Inspection: Oct 2018 (completed)
Stormwater model of basin: Nov ‐Dec 2018 (completed)
Develop & evaluate alternatives: Dec 2018 ‐March 2019
Underway –This is the focus of today’s meeting
Concept Design of Preferred Alternative: March – May 2019
Draft DSR: July 2019
Final DSR: August 2019
Tentative Future Project Schedule
Survey and geotech for selected alternative: Fall 2019
Design selected alternative: Fall 2019 – Spring 2020
Project Bidding: Late Spring 2020
Project Construction – Summer 2020
Recent Activities
Recent Community and Coordination Activities
SWG Meeting #1: November 2018
SLCC Presentations : October 2018 and January 2019
Written update to SLCC: February 2019
Meeting with local developer (The Peterson Group): March 6, 2019, regarding development planned this year and in coming years.
Meeting with Anchorage School District: March 28, 2019
Project Phases
1. Drainage Study Report (current)
2. Detailed Design (Plans, Specs, and Estimate)
3. Construction
Phase 1 Goals and Objectives
1. To identify alternatives to disconnect the existing overflow to the pond.
2. To select a preferred alternative that meets the technical and community objectives. E.g. Do not worsen flooding compared to existing conditions, and do not allow stormwater into the pond.
3. To complete concept design of the preferred alternative.
Planning for Risk
Q. What is a 10‐year rainfall event?
A. It has a statistical likelihood of occurring once every 10 years.
In other words, it has a 10% likelihood of occurring in any given year.
Q. What is a 100‐year rainfall event?
A. It has a statistical likelihood of occurring once every 100 years.
In other words, it has a 1% likelihood of occurring in any given year.
Planning for New Rainfall Data
Design Storm Old Depth (in) New Depth (in) Percent
Increase
10‐year, 24‐hour 1.77 2.28 29%
100‐year, 24‐hour 2.48 3.59 45%
Baseline Modeling
Existing Conditions Model
Shows how the drainage system is performing today, with the pond overflow in place.
Looked at performance during a 10‐year, 24‐hour event and a 100‐year 24‐hour event.
The model simulates rainfall as it hits the ground surface, flows toward the drainage system, and is routed to either the pond or toward Dimond.
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Sand
Lake
Roa
d
Dimond Boulevard
Kincaid Road
Dimond Boulevard
Westp
ark D
rive
Lucy
Stre
et
Katahdin Drive
Tarsus Drive
Tyre
Drive
Seac
liff St
reet
Seav
iew St
reet
Big Bend Loop
80th Avenue
Kenai Fjords Loop
Gate
Cree
k Driv
e
Cobbler Drive
73rd Avenue
Skyhills Drive
Kidro
n Street
Yukon Charlie Loop
82nd Avenue
Dry C reek Loop
Quiet Circle
Wandering Drive
Somm
ers Pl
ace
Lost Circle
Unnamed Road
Violet
Plac
e
Sky M
ountain
Circle
Skylark Avenue
Heather Wood Circle
Flagstone CircleSk
y Mou
ntain Lane
80th Avenue
Unnamed R oad
Wand
ering
Driv
e
Unna
med R
oad
Unnamed Road
Unnamed Road
Unna
med R
oad
Legend!( Existing Storm Drain Structure
Existing Storm Drain Pipe
³
Pond
DimondBore
EmergencyOverflow
Westpark Sag
Westpark Stormwater Bypass ReconstructionExisting Conditions
CurrentDevelopment
CurrentDevelopment
CurrentDevelopment
School Site
Station (ft)4+804+604+404+204+003+803+603+403+203+002+802+602+402+202+001+801+601+401+201+00
Eleva
tion (
ft)
141.5141
140.5140
139.5139
138.5138
137.5137
136.5136
135.5135
134.5134
133.5133
132.5132
131.5131
130.5130
129.5129
128.5
_ __ _
_
J-M-WP
D-23-C
B
Link ID L-M-WPD-22-P
J-M-WP
D-22-C
B
Link ID L-M-WPD-21-P
J-M-WP
D-21-M
H
Link ID L-M-WPD-20-P
J-M-WP
D-20-C
B
Link ID L-M-WPD-19-P
J-M-WP
D-19-C
B
Sample of Existing Conditions Model - Westpark Drive 10-Year Storm
100-Year Storm
High Water Level
Manhole
Pipe
Ground Surface
Manhole
Pipe
Pipe
Ground SurfaceHigh Water Level
Baseline Modeling
Full Build Conditions Model
Shows how today’s drainage system would perform once the basin development is complete.
Future basin development includes: Sonoma Glen Phases 2, 3, and 4 The school site The northwest property
This was used as a baseline for “don’t make flooding worse.”
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Sand
Lake
Roa
d
Dimond Boulevard
Kincaid Road
Dimond Boulevard
Westp
ark D
rive
Lucy
Stre
et
Katahdin Drive
Tarsus Drive
Tyre
Drive
Seac
liff St
reet
Seav
iew St
reet
Big Bend Loop
80th Avenue
Kenai Fjords Loop
Grand Teton Loop
Gate
Cree
k Driv
e
Cobbler Drive
73rd Avenue
Skyhills Drive
Kidro
n Street
Yukon Charlie Loop
82nd Avenue
Dry Creek Loop
Quiet Circle
Wandering Drive
Somm
ers Pl
ace
Lost Circle
Unnamed Road
Park
West
Circle
Violet
Plac
e
Sky M
ountain
Circle
Skylark Avenue
Heather Wood Circle
Flagstone CircleSk
y Mou
ntain Lane
80th Avenue
Unnamed R oad
80th Avenue
Wand
ering
Driv
e
Unna
med R
oad
Unnamed Road
Unnamed Road
Unna
med R
oad
Legend!( Future Storm Drain Structure
Future Storm Drain Pipe!( Existing Storm Drain Structure
Existing Storm Drain Pipe
³
Pond
DimondBore
EmergencyOverflow
Westpark Sag
Westpark Stormwater Bypass ReconstructionFull Build Conditions
CurrentDevelopment
CurrentDevelopment
Current & FutureDevelopment
School SiteFutureDevelopment
FutureDevelopment
Alternatives Modeling and Results
Alternatives Analysis
Evaluated many different configurations
In each case, the priorities were: No stormwater to the pond. Do not make flooding/ponding worse.
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Sand
Lake
Roa
d
Dimond Boulevard
Kincaid Road
Dimond Boulevard
Westp
ark D
rive
Lucy
Stre
et
Katahdin Drive
Tarsus Drive
Tyre
Drive
Seac
liff St
reet
Seav
iew St
reet
Big Bend Loop
80th Avenue
Kenai Fjords Loop
Grand
Teton Loop
Gate
Cree
k Driv
e
Cobbler Drive
73rd Avenue
Skyhills Drive
Kidro
n Street
Yukon Charlie Loop
82nd Avenue
Dry C reek Loop
Quiet Circle
Wandering Drive
Somm
ers Pl
ace
Lost Circle
Unnamed Road
Park WestCircle
Violet
Plac
e
Sky M
ountain
Circle
Skylark Avenue
Heather Wood Circle
Flagstone CircleSk
y Mou
ntain Lane
80th Avenue
Unnamed R oad
Wand
ering
Driv
e
Unna
med R
oad
Unnamed Road
Unnamed Road
Unna
med R
oad
Westpark Stormwater Bypass Reconstruction
Legend!( Summer 2019 Storm Drain Structure
Summer 2019 Storm Drain Pipe!( Proposed Storm Drain Structure
Proposed Storm Drain Pipe!( Existing Storm Drain Structure
Existing Storm Drain Pipe
³
Emergency Overflow Removed
Pond
DimondBore
Bypass + School Detention + Dimond Detention
School Detention
Dimond Detention
750 LF New ParallelBypass Pipe (30" to 42")
750 LF Upsized Pipe (42")
1,800 LF New ParallelBypass Pipe (30")
CurrentDevelopment
CurrentDevelopment
Current & FutureDevelopment
School SiteFutureDevelopment
FutureDevelopment
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Sand
Lake
Roa
d
Dimond Boulevard
Kincaid Road
Dimond Boulevard
Westp
ark D
rive
Lucy
Stre
et
Katahdin Drive
Tarsus Drive
Tyre
Drive
Seac
liff St
reet
Seav
iew St
reet
Big Bend Loop
80th Avenue
Kenai Fjords Loop
Grand
Teton Loop
Gate
Cree
k Driv
e
Cobbler Drive
73rd Avenue
Skyhills Drive
Kidro
n Street
Yukon Charlie Loop
82nd Avenue
Dry C reek Loop
Quiet Circle
Wandering Drive
Somm
ers Pl
ace
Lost Circle
Unnamed Road
Park WestCircle
Violet
Plac
e
Sky M
ountain
Circle
Skylark Avenue
Heather Wood Circle
Flagstone CircleSk
y Mou
ntain Lane
80th Avenue
Unnamed R oad
Wand
ering
Driv
e
Unna
med R
oad
Unnamed Road
Unnamed Road
Unna
med R
oad
Westpark Stormwater Bypass Reconstruction
Legend!( Summer 2019 Storm Drain Structure
Summer 2019 Storm Drain Pipe!( Proposed Storm Drain Structure
Proposed Storm Drain Pipe!( Existing Storm Drain Structure
Existing Storm Drain Pipe
³
Emergency Overflow Removed
Pond
DimondBore
Extended Bypass + Dimond Detention
Dimond Detention
2,300 LF New ParallelBypass Pipe (30" to 42")
750 LF Lowered andUpsized Pipe (48")
1,800 LF New ParallelBypass Pipe (48")
CurrentDevelopment
CurrentDevelopment
Current & FutureDevelopment
School SiteFutureDevelopment
FutureDevelopment
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Sand
Lake
Roa
d
Dimond Boulevard
Kincaid Road
Dimond Boulevard
Westp
ark D
rive
Lucy
Stre
et
Katahdin Drive
Tarsus Drive
Tyre
Drive
Seac
liff St
reet
Seav
iew St
reet
Big Bend Loop
80th Avenue
Kenai Fjords Loop
Grand
Teton Loop
Gate
Cree
k Driv
e
Cobbler Drive
73rd Avenue
Skyhills Drive
Kidro
n Street
Yukon Charlie Loop
82nd Avenue
Dry C reek Loop
Quiet Circle
Wandering Drive
Somm
ers Pl
ace
Lost Circle
Unnamed Road
Park WestCircle
Violet
Plac
e
Sky M
ountain
Circle
Skylark Avenue
Heather Wood Circle
Flagstone CircleSk
y Mou
ntain Lane
80th Avenue
Unnamed R oad
Wand
ering
Driv
e
Unna
med R
oad
Unnamed Road
Unnamed Road
Unna
med R
oad
Westpark Stormwater Bypass Reconstruction
Legend!( Summer 2019 Storm Drain Structure
Summer 2019 Storm Drain Pipe!( Proposed Storm Drain Structure
Proposed DitchProposed Storm Drain Pipe
!( Existing Storm Drain StructureExisting Storm Drain Pipe
³
Emergency Overflow Removed
Pond
DimondBore
Extended Bypass with Westpark Ditch + Dimond Detention
Dimond Detention
1,600 LF New Parallel Ditch(12' Wide and 3' Deep)
750 LF Lowered andUpsized Pipe (48")
1,800 LF New ParallelBypass Pipe (48")
CurrentDevelopment
CurrentDevelopment
Current & FutureDevelopment
School Site
700 LF New ParallelBypass Pipe (36" to 42")
FutureDevelopment
FutureDevelopment
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!(!(!(!(
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Sand
Lake
Roa
d
Dimond Boulevard
Kincaid Road
Dimond Boulevard
Westp
ark D
rive
Lucy
Stre
et
Katahdin Drive
Tarsus Drive
Tyre
Drive
Seac
liff St
reet
Seav
iew St
reet
Big Bend Loop
80th Avenue
Kenai Fjords Loop
Grand
Teton Loop
Gate
Cree
k Driv
e
Cobbler Drive
73rd Avenue
Skyhills Drive
Kidro
n Street
Yukon Charlie Loop
82nd Avenue
Dry C reek Loop
Quiet Circle
Wandering Drive
Somm
ers Pl
ace
Lost Circle
Unnamed Road
Park WestCircle
Violet
Plac
e
Sky M
ountain
Circle
Skylark Avenue
Heather Wood Circle
Flagstone CircleSk
y Mou
ntain Lane
80th Avenue
Unnamed R oad
Wand
ering
Driv
e
Unna
med R
oad
Unnamed Road
Unnamed Road
Unna
med R
oad
Westpark Stormwater Bypass Reconstruction
Legend!( Summer 2019 Storm Drain Structure
Summer 2019 Storm Drain Pipe!( Proposed Storm Drain Structure
Proposed Pipe or DitchProposed Storm Drain Pipe
!( Existing Storm Drain StructureExisting Storm Drain Pipe
³
Emergency Overflow Removed
Pond
DimondBore
Extended Bypass + Small Dimond Detention + Second Dimond Bore
Small DimondDetention
1,600 LF New ParallelBypass Pipe OR Ditch
750 LF Lowered andUpsized Pipe (48")
1,800 LF New ParallelBypass Pipe (48")
CurrentDevelopment
CurrentDevelopment
Current & FutureDevelopment
School Site
700 LF New ParallelBypass Pipe (36" to 42")
Second Dimond Bore (28" O.D.)
FutureDevelopment
FutureDevelopment
Alternatives Modeling and Results
Bypass Pipe vs Ditch Along Westpark Drive
Pipe expected to be more expensive.
Pathway conflict—would have to move the pathway.
General aesthetic differences.
Alternatives Modeling and Results
Bypass Pipe vs Ditch Along Westpark Drive
Existing Westpark Drive
Example Open Ditch in Urban Area
Alternatives Modeling and Results
Westpark Stormwater Bypass ReconstructionAlternative Evaluation
Bypass(various sizes &
alignments evaluated)
Bypass + School
Detention
Bypass + School Detention + Dimond
Detention
Extended Bypass + Dimond Detention
Extended Bypass w/ Westpark Ditch + Dimond Detention
Extended Bypass +Small Dimond Detention +
Second Dimond Bore
Dimond Bore Area X X
Westpark Drive X
Kenai Fjords Loop
Grand Teton X
Big Bend Loop X
West Gate Area X
Dimond Bore Area X X
Westpark Drive X
Kenai Fjords Loop
Grand Teton
Big Bend Loop X
West Gate Area
Key
X = Worsens Drainage Issues
= Does Not Worsen or Improves Drainage Issues
Gray Text = Other Fatal Flaw (e.g. right‐of‐way constraint)
Even
t
Location
Alternatives
10‐year
100‐year
AWR Engineering Page 1 of 1 4/1/2019
Project Budget Status
Westpark Stormwater Bypass ReconstuctionBudget Summary
Item Amount ($) Notes
2018 Bond $2,140,000 Bond Approved in April 2018Available Project Amount $2,030,000 5% of the Bond goes to MOA Central Services and Bond CostCurrent Project Budget $2,030,000
Design $470,000Utilities $100,000ROW $35,000Construction $903,000 Expected to be underfunded based on draft alternatives15% Contingency $225,000Overhead $300,000
Amount Spent to Date $113,000 Design and OverheadAmount Remaining $1,917,000
AWR is only contracted through final DSR. Amount needed for final design, ROW, and utilities not known until alternative selected.
Closing Questions or Comments?
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