HomeMy WebLinkAboutRaising Angles Hydrological Assessment Report Raising
Daycare
City of Meridian,
Ada County, Idaho
HYDROLOGICAL
ASSESSMENT REPORT
Prepared For:
Engineered Structures Inc
Boise, ID
Prepared By:
LEI
ENGINEERS
SURVEYORS
PLANNERS
3023 E. Copper Point Dr. #201
Meridian, ID 83642
Scott Sherrow, PE
Date:
December 17, 2013
LEI
I
SURE F;g
Raising Angles Daycare
Hydrological Assessment Report
I. Raising Angles Daycare
INTRODUCTION 1
GENERAL PROJECT DESCRIPTION 1
PROJECT DESIGN CONCEPTS 1
HYDRAULIC ASSUMPTIONS: 2
POST DEVELOPMENT CONDITIONS 2
Table 1 —Basin Characteristics Summary 2
Table 2—Storm Water Summary 3
STORMWATER FACILITIES 3
SEEPAGE BED 3
Table 3—Seepage Bed Summary 3
ROADSIDE SWALE 4
Table 4—Roadside Swale Summary 4
OIL/SEDIMENT VAULTS 4
II. Tab 1: Drawing Documents
Post Development Drainage Maps
Grading & Drainage Plan
III. Tab 2: Calculations, Spreadsheets and Computer Model Output
DA#1- Seepage Bed —Volume and Flow
DA#2- Seepage Bed —Volume and Flow
DA#3- Roadside Swale —Volume and Flow
IV. Tab 3: Engineering Support Documentation
Strata's Geotechnical Report—August 14, 2013
Page 0 Project No. 13-30227—Raising Angles Daycare—Meridian- Hydrological Assessment Report
LEI•E.3023 Copper Point Dr.•Meridian,ID 83642• P:208.846.9600
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SUR E OR S
PI P
I. Raising Angles Daycare
INTRODUCTION
The Raising Angles Daycare project is situated within the City of Meridian, Ada County, being located in
the southwest corner of the intersection of E. Pine Ave. and N. Nola Road. ESI is proposing to develop a
+-5,000 sf building on approximately 0.94 acres.
The purpose of this report is to determine the hydrologic impacts that the proposed development may
have on the existing runoff patterns and flow characteristic from the site.
This hydrological assessment was completed after review of the following information: The past
development plans, topographic and boundary map information; historical storm data (Ada County);
available SCS soil maps; and the Geotechnical Engineering Report prepared by Strata, Inc. This data
was then analyzed with the Rational Method utilizing a computer modeling spreadsheet for the drainage
basins. This program provides information on storm runoff volumes, peak rate of discharge, and storage
design storage volume requirements. Design recommendations are based on the results of the analysis.
GENERAL PROJECT DESCRIPTION
The site is bounded on the north by E. Pine Ave., to the south by Oak Harbor Freight Line facilities, to the
east by N. Nola Road and to the west by plated lots. Ground cover consists of bare dirt to light field
grasses.
PROJECT DESIGN CONCEPTS
Storm water runoff from the portions of the building roof surface and hard scape areas will be conveyed to
oil/sedimentation vaults and to the proposed infiltration facilities. Portion of the roof system and
landscape areas not subject to vehicular traffic may be conveyed to depressed areas within the
landscaped areas. The proposed entry road to be constructed on the adjacent lot to the east of the
project site will drain to a temporary roadside swale. For additional information on the drainage basin
locations and limits, refer to the drainage basin maps located in Tab 1 of this report.
On-site storm water improvements for the project will consist of curb and gutters, catch basins, manholes,
storm water conveyance pipelines, roadside swale, oil/sedimentation vaults (pretreatment water quality
structure) and the infiltration facilities. Stormwater utility improvements provided for the project will be in
accordance with ACHD's Storm Water Management Manual, and per ACHD's storm water management
policies as amended by the City of Meridian. The infiltration facilities will consist of underground seepage
beds and a roadside swale.
For the purpose of hydrological analysis and for computer modeling of the Raising Angles Daycare
project, the following basin conditions were modeled utilizing an Excel Spreadsheet
Seepage Beds+ Post-Development runoff - 100 yr event to determine storage and
infiltration requirements and the 25 yr event to determine conveyance
system sizing requirements, Rational Method Runoff.
Page 1 Project No. 13-30227—Raising Angles Daycare—Meridian- Hydrological Assessment Report
LEI•E.3023 Copper Point Dr.•Meridian,ID 83642• P:208.846.9600
LEI
HYDRAULIC ASSUMPTIONS:
LEI utilized the following assumptions in establishing the post-development stormwater runoff conditions
for the proposed Raising Angles Daycare project hydrological assessment/report:
Runoff Evaluation Method: A spreadsheet program based on the Rational Method was utilized.
The following Items were reviewed:
• Established values from the Intensity-Duration-Frequency Curve Chart for the Boise area
from the ACHD's Storm Water Management Manual
• The 100-yr storm event with 60 minute duration was evaluated to determine the
developed runoff volume.
• Existing site conditions
• Drainage patterns
Runoff Coefficient"C": Per Section 8012.2.1 ACHD's Storm Water Management Manual, C
values were chosen. C=0.95, which represents the asphalt paving was used and a value of C =
0.2,which represents landscape areas.
Rainfall Intensity "I": I values, are determined from the Intensity-Duration-Frequency's listed in
Section 8202.1 ACHD's Storm Water Management Manual.
Time to Concentration "Tc": Tc values are calculated for each basin using the FAA Method (Used
by City of Boise). This method analyzes the combination of sheet flow, shallow concentrated
flow, and channel flow characteristics associated for each drainage basin to arrive at an overall
time which represents the length of time required for a particle of water to flow hydraulically from
the most distant point in the watershed to the outlet or design point. The minimum value of 10
minutes was used in the analysis.
POST DEVELOPMENT CONDITIONS
Computer modeling of the design storm for the post-development condition of the Raising Angles
Daycare project utilizing the Rational Method produced the following results, see Table 1&2:
Table 1 —Basin Characteristics Summary
Basin Area Impervious Pervious I Avg. Runoff
Coeff.
(Acres) (Acres) (Acres)
DA#1 0.54 0.34 0.20 0.69
DA#2 0.41 0.16 0.25 0.52
DA#3 0.10 0.10 0.00 0.95
See computer spreadsheets Tab 2 for details.
Page 2 Project No. 13-30227—Raising Angles Daycare—Meridian- Hydrological Assessment Report
LEI:'3023 E.Copper Point Dr.•Meridian,ID 83642• P:208.846.9600
LEI
Table 2—Storm Water Summary
Basin Flow Rate Flow Rate Storage
(Q25) (Q100) 100 yr Vol. Time of Conc.
(cfs) (cfs) (cu-ft) (min)
DA#1 0.88 1.15 1,767 10.00
DA#2 0.50 0.66 1,013 10.00
DA#3 0.22 0.29 440 10.00
See computer spreadsheets Tab 2 for details.
STORMWATER FACILITIES
The stormwater disposal systems are designed to contain the 100-year storm event. The location and
parameters of the seepage bed facilities have been detailed in the construction plans. Construction plans
for the sheets relating to the storm water seepage beds have been included in the Tab 1 of this report.
Storm water from surface runoff and the building will ultimately be conveyed either to the infiltration
facilities or retained on site within the landscape areas.
The storm water infiltration facilities will be configured in accordance with the general guidelines
published by ACHD associated with storm water treatment/retention/infiltration and in accordance with
ACHD's storm water management policies as amended by the City of Meridian.
A typical oil/sedimentation vault has been designed into the stormwater system to provide water quality
treatment of the flowrate of run-off associated with the 100 yr storm event before discharging into the
seepage/infiltration beds. Secondary water quality treatment is provided by maintaining a three foot
separation between the bottom of the facilities and the seasonal high ground water elevation.
SEEPAGE BED
The seepage beds for the Raising Angles Daycare project have been designed to fully contain the 100-
year storm event. For the design of seepage beds, Strata's Geotechnical Report was referenced to
determine soil characteristics & infiltration rates to size the seepage beds and to determine depth to
bedrock.
Using the data from the computer modeling spreadsheet and geotechnical reports recommended
infiltration rates, the required storage volume for the seepage bed was determined. A void space (e) of
40% was assumed and used to size the seepage beds. The Table 3 summarizes seepage beds sizing
results.
Table 3—Seepage Bed Summary
I Seepage dge I Width Length Depth Infiltration Actual
Rate Storage
(ft.) (ft.) (ft.) (in/hr) (cu.ft.)
DA#1 15 50 6 8 1,800
DA#2 15 30 6 8 1,080
See computer spreadsheets Tab 2 for details
Page 3 Project No. 13-30227—Raising Angles Daycare—Meridian- Hydrological Assessment Report
LEI:•3023 E.Copper Point Dr.•Meridian.ID 83649• P:208.846.9600
LEI
ROADSIDE SWALE
The temporary roadside swale providing storm water management for the entry road for the Raising
Angles Daycare project was designed to fully contain the 100-year storm event. Strata's Geotechnical
Report was referenced to determine soil characteristics & infiltration rates to size the facility and to
determine depth to bedrock.
Using the data from the computer modeling spreadsheet and geotechnical reports recommended
infiltration rates, the required storage volume for the roadside swale was determined. A minimum or 6" of
freeboard is provided above the 100 yr ponding elevation. The Table 4 summarizes roadside swale
sizing results.
Table 4— Roadside Swale Summary
BTM. Side Infiltration Actual
Swale Width Length Slope Depth Rate Storage*
(ft.) (ft.) (ft.) (in/hr) (cu.ft.)
DA#3 3 62 4 1 8 478
See computer spreadsheets Tab 2 for details
OIL/SEDIMENT VAULTS
The project's oil/sediment vaults will sized per ACHD's Storm Drain Policy Manual (page 8200-21).
ACHD's Storm Drain Policy Manual specifies the maximum allowable flow through 1000 gallon trap with
20"baffle to be 3.33 cfs. The maximum flow off the site's drainage basins is 1.15 cfs for the 100 year
event. Therefore 1000 gallon trap with 20"baffle spacing will be used.
Page 4 Project No. 13-30227—Raising Angles Daycare—Meridian- Hydrological Assessment Report
LEI:•3023 E.Copper Point Dr.•Meridian,ID 83642• P:208.846.9600
TAB 1
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TAB 2
CALCULATIONS
SPREADSHEETS
COMPUTER MODEL OUTPUT
Raising Angles Daycare:Storage Volume and Pond Sizing Calculations
Basin# DA#1
Seepage Bed# 1
Ste• 1:Wei•hted Coefficient of Runoff for Areas Contributin s to See.a:e B
Building Area 0.00 0.95 0ed
Building/Parking Area/Sidewalk 0.34 0.95 0.3211
0.25 0.05
Landscape Area 0.2
0.54 0.3711
I Cw= 0.69 I
Ste 2:Time to Concentration*
nr .z.
Runoff Flow Length 0 )00.005 0.00 10.00
*Tc was computed with the Kirpitch Method:Tc=.0078(L77(Sa„9) -°.385
**Per ACHD min.Tc allowed shall be 10 minutes
Ste• 3:Peak Dischar•e for Prima Conveyance S stems Drainin.Y •e to See•a Bed
-
Seepage Bed 0.69 2-Year 10.00 1.21 0.54 0.45
0.69 25-Year 10.00 2.37 0.54 0.88
0.69 100-Year 10.00 3.11 0.54 1.15
*Intensity based of Tc(from step 2)and a Storm Interval of 100 years.
**Peak Flow Calculation is based on ACRD requirements for Primary Conveyance in an urban area setting.
Step 4:Calculate Storage Volume(VS)Contributing to Seepage Bed
Seepage Bed 0.69 100-year 1.15 1 0.54 1766.81
*Intensity based on duration of one hour and a storm interval of 100 years.
**Storage Volume Calculation = V=(CiA(3600))*1.15,Tc=60min, 15%Sed Storage Volume
Step 5:Calculate Seepage Bed Dimensions and Storage Volume Provided(V,)
Seepage Bed 50 15 6 40 1800 OK
Step 6:Calculate Storage Volume(V5)Requirements of Seepage Bed
Seepage Bed 4 750.00 8.00 500.00 3.18
*Drain per hour in Cu.Ft./Hr=Area*IR/12
**Hours to completely Drain=(0.90*Req'd volume)/Drain per hour
Raising Angles Daycare:Storage Volume and Pond Sizing Calculations
Basin# DA#2
Seepage Bed# 2
Ste• 1:Wei hted Coefficient of Runoff for Areas Contributin, to See•a,e Bed
Building Area 0.00 0.95 0
Building/Parking Area/Sidewalk 0.16 0.95 0.1501
Landscape Area 0.25 0.25 0.0625
0.41 0.2126
I Cw= 0.52
Ste• 2:Time to Concentration*
Runoff Flow Length 0 0.005 0.00 10.00
*Tc was computed with the Kirpitch Method:Tc=.0078(L)'77(Savg)-°385
**Per ACHD min.Tc allowed shall be 10 minutes
Ste. 3:Peak Dischar.e for Prima Conve ance S stems Drainin. toSee.a.eBed
Seepage Bed 0.52 2-Year 10.00 1.21 0.41 0.26
0.52 25-Year 10.00 2.37 0.41 0.50
0.52 100-Year 10.00 3.11 0.41 0.66
*Intensity based of Tc(from step 2)and a Storm Interval of 100 years.
**Peak Flow Calculation is based on ACHD requirements for Primary Conveyance in an urban area setting.
Step 4:Calculate Storage Volume(Vs)Contributing to Seepage Bed
b a . s
Seepage Bed 0.52 100-year 1.15 1 0.41 1012.19
*Intensity based on duration of one hour and a storm interval of 100 years.
**Storage Volume Calculation = V=(CiA(3600))*1.15,Tc=60min, 15%Sed Storage Volume
Step 5:Calculate Seepage Bed Dimensions and Storage Volume Provided(Vs)
Seepa.a Bed 30 15 6 40 1080 OK
Step 6:Calculate Storage Volume(Vs)Requirements of Seepage Bed
Seepage Bed 450.00 8.00 300.00 3.04
*Drain per hour in Cu.Ft./Hr=Area*IR/12
**Hours to completely Drain=(0.90*Req'd volume)/Drain per hour
Raising Angles Daycare:Storage Volume and Pond Sizing Calculations
Basin# DA#3
Pond#
Ste• 1:Wei,hted Coefficient of Runoff for Areas Contributin• to See•a•e Bed
: 1-A,-::::-A- -fi'
Building Area 0.00 0.95 0
Parking Area/Sidewalk (Hardscape) 0.10 0.95 0.09215
Landscapee Area 0 0.25 0
0.10 0.09215
I Cw= 0.95 I
Ste• 2:Time to Concentration*
-i ' a: ' � ri" '- ,ate,: ' „ ; ,,
Runoff Flow Length 0 0.005 0.00 10.00
*Tc was computed with the Kirpitch Method:Tc=.0078(L)'"(San)-8 385
**Per ACHD min.Tc allowed shall be 10 minutes
Ste 3:Peak Dischar.e for Prima Conve ance S stems Dramin• to Pond
Pond 0.95 2-Year 10.00 1.21 0.10 0.11
0.95 25-Year 10.00 2.37 0.10 0.22
0.95 100-Year 10.00 3.11 0.10 0.29
*Intensity based of Tc(from step 2)and a Storm Interval of 100 years.
**Peak Flow Calculation is based on ACHD requirements for Primary Conveyance in an urban area setting.
Step 4:Calculate Storage Volume(V,)Contributing to Pond
Pond 0.95 NNW= 0.34 WQ*** 0.10 N/A
0.95 100- ear 1.15 1 0.10 439
*Intensity based on duration of one hour and a storm interval of 100 years.
**Storage Volume Calculation = V=(CiA(3600))*1.15,Tc=60min, 15%Sed Storage Volume
***lps 0.34"at Boise Airport-80th Percentile Storm
Step 5:Calculate Pond Dimensions and Storage Volume Provided(V)
•
•
,..?, a ",.i " :ro ,..
WQ-Pond 0 0 0 0 0 FAIL
100 yr Pond One Cell 62 3 1 4 478 OK
*Calculation of Vp(Storage Volume Provided)subtracts 1-feet of depth,and subsequent storage volume,
of seepage bed for freeboard per ACHD requirements.
Step 6:Calculate Storage Volume(Vs)Requirements of Pond
s. A • -- ; A rf ,'. . o
WQ-Pond 0.00 80.00 0.00 #DIV/0!
100 yr Pond One Cell 30.00 8.00 20.00 11
*Drain per hour in Cu.Ft./Hr=Area*IR/12
**Hours to completely Drain=(0.90*Req'd volume)/Drain per hour