training agenda engineer module – september 21, 2005 afternoon session: 1:30 pm to 4:00 pm...
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LID Project ObjectivesTRANSCRIPT
TRAINING AGENDA Engineer Module – September 21, 2005
Afternoon Session: 1:30 pm to 4:00 pm
Engineers Training Exercise
Break: 2:15 – 2:30pm
– LID Project Objectives
– Master Planning Process• Integration into Site Analysis, Benefit Analysis, Site
Design Selection, Plan Development• Green Roof
– Discuss Traditional Site Plan vs. LID Approach
LID Project Objectives
LID Project Objectives
• LID approaches and techniques for the design of the MARFORLANT headquarters facility
– Feasibility– Potential effectiveness
LID Project Objectives
• Utilizing LID techniques and practices to meet:– Regulatory requirements– Federal government program goals
• Water conservation• Energy conservation• Environmental stewardship
– Natural resource program management objectives
MARFORLANT: Master Planning Process
• Meet Virginia Department of Conservation and Recreation (VDCR) stormwater management regulations.
• rainfall used for non-potable uses– irrigation or toilet flushing
• Ancillary benefits energy conservation – vegetated roof– strategic siting of vegetation.
MARFORLANT: Master Planning Process
• “GOVERNMENT BY EXAMPLE”
• Eliminate pond option by replacing the hydrologic and hydraulic functions with LID practices such as bioretention. – eliminating pond maintenance – pond vector issues.
Master Planning Process:Case Study MARFORLANT
• Integration into:–Site Analysis–Benefit Analysis–Site Design Selection–Plan Development
Master Planning Process: Site description
• 7.1 acres in size.• Site slopes gently
from the north and south
• Low point in the center of the property.
• mix of woods and grass
• The soils on site are compacted.
Master Planning Process: Proposal
• 55,000 sq. ft. building northern portion of site
• 280 parking spaces• Future building
planned western side of proposed facility.
• Conventional stormwater on western edge
• Woods should remain undisturbed
Master Planning Process: Hydrologic Analysis
• The Commonwealth of Virginia requires peak runoff post-development condition to equal or be below the discharge from the pre-development condition for:– 2-year 24-hour storm (with a six-inch depth )
• LID practices is three (3) percent, or 0.2 acres– 10-year 24-hour storm event for urban areas
• LID practices is eight (8) percent, or 0.6 acres
• Pre-and Post-development conditions are compared to determine a storage volume
Master Planning Process: Non-potable water
• Secondary non-potable usage – toilet flushing, cooling, irrigation
• Daily water demand 4,500 gpd for 300 office workers (15 gal per person per day)
• Cistern size of 14 diameter and height of 37 ft to capture and reuse water.
Master Planning Process: Non-potable water
LID Site Design
• Requirement of 8% of the site in LID features (10 yr 24 hr storm)– Runoff will sheet flow to a centralized
bioretention facility with several perimeter bioretention facilities
– Permeable surfaces on walkways– Green roof
Master Planning Process
Green Roof
Green Roof
• Conditions that have spurred green roof development– Prevalence of combined sewer systems– Antiquated and over-taxed sewer and waste
treatment facilities– Widespread pollution of rivers and estuaries– Frequent nuisance flooding– Limited space for instituting large
management facilities
Green Roof (continued)
• Driving factors for Green roof at MARFORLANT facility– Mitigate water runoff impacts – Compensate for the loss of green space – Limited treatment options for site are limited
• due to location of low point and high water table– Increases service life of roofing system– Reducing energy cost
Layers of Green Roof
• Waterproofing membrane• Root barrier (if the waterproofing is not
certified as root resistant)• Drainage layer• Separation layer• Growth media layer• Plants
Green Roof: Pollution Removal
• It is estimated 30% of all nitrogen and phosphorus in local streams is from roof runoff
• Green roof have demonstrated the removal of:– 68% of total phosphorus – 80% of total nitrogen
Green Roof Benefits: Energy
• Estimated 10% reduction in air-conditioning related energy costs
• Roofing system is expected to last 2-3 times longer than normal
Traditional Site Plan vs. LID Approach
Traditional Site Plan vs. LID Approach
Conventional
• large capital investments in complex and costly engineering strategies
• pipes water to low spots as quickly as possible
LID Design
• Integrates, green space, native landscape, natural hydrology functions to generate less runoff.
• Uses micro-scale techniques to manage precipitation close to where it hits the ground
Traditional Site Plan vs. LID Approach
Conventional vs. LID:
Comparision of CN and Peak Discharge
0102030405060708090
CN () Peak Discharge(CFS) 2-year Storm
3” Depth
Peak Discharge(CFS) 10-year Storm
5” Depth
Conventional CN ()LID DesignExisting Condition
Conventional vs. LID
Volume Comparision
0
0.5
1
1.5
2
2.5
3
3.5
4
Volume (Depth in Inches) 2-YearStorm Event
Volume (Depth in Inches) 10-Year Storm Event
Volu
me
(dep
th in
) Conventional CN
LID Design
Existing Condition
Conventional vs. LID Total costs
Cost per length of pipe per ftC = 0.54D1.3024
for D = $14.40 (12in) D = $30.10 (24 in)
C ($/ft) = 14.45 (12 in) – 37.77 (24 in)
1999 dollars
Cost of grass swale per ft
C/L = K
K = 5-14
C ($/ft) = 5 - 14
No land cost where considered, but could be significant
Cost Savings of LID Techniques
• Reduced downstream erosion and flood control. – preventing costly clean up and stream bank
restorations.
• Infrastructure and development costs. – LID techniques reduces infrastructure
requirements • decreases the amount of pipes, roadways,
detention facilities
Cost Savings of LID Techniques
• Improved groundwater recharge, drinking water, and decreased treatment costs. – Atlanta’s tree cover has saved over $883
million by reducing the need for stormwater facilities.
– forest cover in the source area can reduce treatment cost 50 to 55%
– Every 10% increase in forest cover • treatment and chemical costs decreased
approximately 20%
Funding Aspects
Funding
• Joint Effort – Department of Energy National Renewable
Energy Research Laboratory (NREL)– Federal Management Program (FEMP)– Atlantic Division of the Naval Facilities
Engineering Command (LANTDIV)
Design Exercise
•H and H methods•Strategies and Techniques•Results
Picture NRCL Norfolk
VS/VR
Solution of Runoff Equation
PG Chart
Filterra Sizing/Freq DistRainfall
Runoff Volume (cu ft
/ hr)
Runoff Treated (cu ft / hr)
Cumulative Frequency
Probability Frequency
(c) x (e) (cu ft / hr)
(b) x (e) (cu ft / hr)(in / hr)
0.02 17 17 0.421 0.4205 7.25 7.25
0.04 34 34 0.603 0.1822 6.28 6.28
0.06 52 52 0.713 0.1106 5.72 5.72
0.08 69 69 0.785 0.0717 4.95 4.95
0.10 86 86 0.835 0.0502 4.33 4.33
0.13 108 108 0.875 0.0393 4.24 4.24
0.15 129 129 0.903 0.0285 3.69 3.69
0.20 172 172 0.938 0.0352 6.07 6.07
0.25 216 216 0.957 0.0188 4.05 4.05
0.30 259 259 0.969 0.0117 3.03 3.03
0.35 302 302 0.976 0.0069 2.08 2.08
0.40 345 303 0.981 0.0054 1.64 1.86
0.45 388 303 0.986 0.0046 1.39 1.78
0.50 431 303 0.988 0.0025 0.76 1.08
0.55 474 303 0.990 0.0018 0.55 0.85
0.60 517 303 0.992 0.0019 0.58 0.98
0.65 560 303 0.993 0.0012 0.36 0.67
0.70 603 303 0.994 0.0012 0.36 0.72
0.75 647 303 0.995 0.0008 0.24 0.52
0.80 690 303 0.996 0.0007 0.21 0.48
0.90 776 303 0.997 0.0014 0.42 1.09
1.00 862 303 0.998 0.0008 0.24 0.69
1.50 1293 303 1.000 0.0020 0.61 2.59
2.00 1724 303 1.000 0.0001 0.03 0.17
Totals 1.0000 59.07 65.17
Simple Method
L = 0.226 x R x C x A
Where: L = Annual load (lbs) R = Annual runoff (inches) C = Pollutant concentration (mg/l) A = Area (acres) 0.226 = Unit conversion factor
Simple Method
D = L x (1-E)
Where: D = Annual load reduction (lbs) L = Annual load (lbs) E = Pollutant removal efficiency
(fraction)
Bioretention Files
AB = area of bioretention, ft2
C = rational c coefficientI = rainfall intensity, in/hrA = drainage area, acresTc = time of concentration, minDs = storage depth in
bioretention, in.Db = bioretention media depth,
ftIr = soil infiltration rate, in/hr
Low Impact Development Objective
Flat
ten
Slop
e
Incr
ease
Flo
w P
ath
Incr
ease
She
et F
low
Incr
ease
Rou
ghne
ss
Min
imiz
e D
istu
rban
ce
Lar
ger
Swal
es
Flat
ten
Slop
es o
n Sw
ales
Infil
trat
ion
Swal
es
Veg
etat
ive
Filte
r St
rips
C
onst
rict
ed P
ipes
D
isco
nnec
ted
Impe
rvio
us A
reas
R
educ
e C
urb
and
Gut
ter
Rai
n B
arre
ls
Roo
ftop
Sto
rage
B
iore
tent
ion
Re-
Veg
etat
ion
Veg
etat
ion
Pre
serv
atio
n
Increase Time of Concentration X X X X X X X X X X X
Increase Detention Time X X X X
Increase Storage X X X X X X
Lower Post Development CN X X X X X
LID Techniques and ObjectivesLow-Impact Development Technique
Maintain Time ofConcentration (Tc)
Low Impact Developmentobjective to Maintain Time ofConcentration (Tc) B
alan
ce c
ut a
nd fi
ll on
lot.
Net
wor
k Sm
alle
r Sw
ales
Clu
ster
s of
Tre
es a
ndSh
rubs
in F
low
Pat
h
Prov
ide
Tre
eC
onse
rvat
ion
on L
ots
Elim
inat
e St
orm
Dra
inPi
pes
Dis
conn
ect I
mpe
rvio
usA
reas
Save
Tre
es in
Sm
alle
rC
lust
ers
Ter
race
Yar
ds
Dra
in fr
om H
ouse
and
then
Red
uce
Gra
des
Minimize Disturbance X X X X X
Flatten Grades X X
Reduce Height of Slopes X X
Increase Flow Path (Divert andRedirect)
X X X X
Increase Roughness “n” X X X X X
X
X X
X
X
X X
Low-Impact Development Technique
Example Retrofit: Anacostia Annex of the Washington Navy Yard
• Currently no stormwater management – quantity or quality controls
• Replacement of the parking area is required. • Drainage inlets and old brick drainage
structures need to be replaced. • Sidewalk needs to be replaced • The site does not comply with Americans with
Disabilities Act (ADA) Standards.
PROJECT OBJECTIVES
• Integrate LID practices into the repaving of parking areas
• Repair the sidewalks• Re-landscape Pollutants of concern for this watershed are:
– oils and grease– total suspended solids– nitrogen and phosphorus.
RANK AND PRIORITIZE OPPORTUNITES
• Greatest potential to reduce non-point source pollutant loads
• Minimal costs for new materials • Minimal maintenance cycles, costs, and
training• Ancillary benefits (landscaping, energy
conservation, water conservation)
SITE CONDITIONS• The site has minimal
topographic relief. • groundwater table is
approximately 3 feet below the surface.
• soils have poor infiltration rates.
• There is an existing drainage system below the buffer.
LID Site Conditions
Results
MWR Pics
Addressing Drainage (1-5)
• Drainage Areas One through Three: – three bioretention cells, a bioretention swale, and a
footpath using permeable pavers.
• Drainage Area Four: – A tree box filter
• Drainage Area Five: – Permeable pavers will be constructed in the existing
valley
Addressing Drainage (6-9)• Drainage Area Six: A bioretention cell will be
constructed within a vegetated island.
• Drainage Area Seven: Pavement will be removed and replaced with a bioretention cell.
• Drainage Area Eight: Permeable pavers will be constructed, a sand layer may be incorporated to increase efficiency.
• Drainage Area Nine: A bioretention cell will be located to the east of the access road.
LID Site Design
Site
Proposed Conventional
Composite Curve Number Calculation for Existing Condition
Weighted CN = Sum of Products ÷ Drainage Area
Curve Number Existing Condition and Proposed Condition
Condition Runoff (in)
Existing (CN = 63) 1.5
Proposed (CN = 80) 2.9
Proposed LID
Conventional vs. LID
Condition CN Tc
Peak Discharge (CFS) Runoff depth (in.)
2-year (3” depth)
10-year (5” depth)
2-year
10-year
Existing Condition 63 0.24 2 10 0.4 1.5
Proposed Condition – conventional CN
80 0.22 9 23 1.3 2.9
Proposed Condition using LID site design
73 0.24 6 17 0.9 2.3
Conventional
LID
Conventional
LID