SWM_Report.pdf

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Attached to: Greenbelt Park Federal contract opportunity
Solicitation number: 693C73-19-B-000004
Issued by: Department of Transportation Federal Highway Administration

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December 1, 2014

Stormwater Management Report

FHWA/NPS	Project	No.	PRA‐GREE	11(1)
MDE	No.	11‐SF‐0286

Construction	of	New	Bridge	Over	Still	Creek	and	Rehabilitation	of	Roads
and	Parking	Areas

Greenbelt Park, National Park Service

Prince George’s County, Maryland

Owner:				Greenbelt	Park,	National	Park	Service
6565	Greenbelt	Road	Greenbelt,
Maryland	20770

Applicant: Kevin S. Rose

Federal	Highway	Administration
Eastern	Federal	Lands	Highway	Division
21400	Ridgetop	Circle
Sterling,	Virginia	20166
Phone:	571‐434‐1592	/	Fax:	571‐434‐1577

Kevin.Rose@dot.gov

Table of Contents

Project Introduction

Summary of Recommendations

Overview of Project

Purpose and Scope

Project Location

ESD Alternatives Analysis

Alternative Surfaces

A‐1. Green Roofs

A‐2. Permeable Pavements

A‐3. Reinforced Turf

Nonstructural Practices

B‐1. Disconnection of Roof

B‐2. Disconnection of Non‐Rooftop Runoff

B‐3. Sheetflow to Conservation Areas

Micro‐Scale Practices

M‐1. Rainwater Harvesting

M‐2. Submerged Gravel Wetlands

M‐3. Landscape Infiltration

M‐4. Infiltration Berms

M‐5. Dry Wells

M‐6. Micro‐Bioretention

M‐7. Rain Gardens

M‐8. Swales

M‐9. Enhanced Filters

Technical Analysis and Design

Hydrologic Analysis

Hydraulic Analysis

CONCLUSION

List of Figures

Figure 1 – Project Vicinity Map

Figure 2 – Project Location Map

List of Tables

Table 1 – Existing Impervious Area

Table 2 – Increase in Impervious Area

Table 3 – Disconnection of Non‐Rooftop Runoff Summary

Appendices

Appendix A – Hydrologic Supporting Information

A‐1 – SWM DA and Disconnection of Non‐Rooftop Runoff locations

A‐2 – Soil Map

Appendix B – Satellite Imagery

Appendix C ‐ USGS National Hydrography Dataset (NHD)

Appendix D: Soils Information

Appendix E: Boring Locations Map

Appendix F: Maryland’s Geologic Map

Appendix G: Boring Logs

1 Stormwater Management Report PRA‐GREE 11(1)

PROJECT

INTRODUCTION

The

project

will

involve

improvement

the

roads

and

parking

lots

open

public

the

Greenbelt

National

Park

Prince

George’s

County,

MD.

According

the

park

official,

the

roads

had

suffered

damage

during

potentially

year

storm

June

2009

when

the

water

surface

had

come

within

foot

two

overtopping

the

road.

The

project

includes

culvert

replacements,

bridge

construction,

stormwater

management

and

pavement

rehabilitation.

SUMMARY	OF	RECOMMENDATIONS
The	following	are	the	hydraulic	recommendations	for	the	project:

1. The

existing

–

10.25’

span

6’

rise

corrugated

metal

arch

culverts

(Appendix

A‐1)

the

Park

Central

(Rte.

11)

the

Still

Creek

crossing

should

replaced

70’

long,

single

span

bridge.

addition,

relief

24”

corrugated

metal

pipes

(CMPs)

‐

one

side

and

the

other,

should

installed

reconnect

the

floodplain.

2. The

Still

Creek

channel

should

lined

with

Class

riprap

(FP

14),

countermeasure

for

scour.

Also

the

existing

scour

hole

should

filled

with

native

channel

material.

3. The

existing

–

36”

reinforced

concrete

pipes

(RCP)

(Appendix

A‐2)

Main

Entrance

Rd.

(Rte.

10)

should

replaced

7’

span

4’

rise

reinforced

concrete

box

(RCB).

4. The

existing

36”

CMP

(Appendix

A‐3)

Rte.

should

replaced

10’

span

6’

rise

reinforced

concrete

box

(RCB).

5. Wet

swales

and

disconnection

non‐rooftop

runoff

should

used

satisfy

MD’s

stormwater

management

requirements.

2 Stormwater Management Report PRA‐GREE 11(1)

OVERVIEW OF PROJECT

PURPOSE

AND

SCOPE

Still

Creek

currently

conveyed

under

the

Park

central

Road

via

two

10.25

feet

span

feet

rise

corrugated

metal

arch

culverts.

The

culverts

drain

urban

watershed

approximately

2.4

square

miles

and

appear

sized

adequately

but

urbanization

upstream

the

park

could

causing

increased

peak

runoff

and

degradation

the

stream

profile.

According

the

park

personnel,

year

storm

event

June

2009

had

caused

the

Still

Creek

come

within

foot

two

overtopping

the

road.

The

storm

appeared

have

accelerated

the

channel

degradation

and

piping

through

the

existing

culverts.

Due

this,

the

park

had

requested

Eastern

Federal

Lands

Highway

Division

(EFLHD)

assess

the

pavement

and

culvert

the

Still

Creek

crossing.

EFLHD

conducted

site

visit

October

2009

and

noticed

that

the

pavement

was

sagging

few

inches

above

the

existing

culverts.

Per

park

personnel,

this

sagging

had

not

changed

significantly

since

the

June

2009

storm.

Two

posts

supporting

the

timber

guardrail

along

the

curve

were

leaning

back

and

rail

had

rotated.

The

south

culvert

was

carrying

the

low

flow

and

piping

was

observed

between

the

two

culverts

the

eastern

fill

slope.

five

feet

deep

scour

hole

was

observed

the

outlet

and

the

culvert

outlets

were

perched

approximately

feet

above

the

water

surface.

The

culvert

bottoms

were

corroded

and

the

channel

appeared

have

degraded

both

upstream

and

downstream

the

culverts.

Also,

bank

erosion

the

Still

creek

had

caused

trees

fall

into

the

stream.

Due

the

above

mentioned

conditions,

the

park

had

initially

requested

EFLHD

repair

the

damage

sustained

the

Still

Creek

culverts

and

the

pavement

above

it.

But

further

site

investigation

had

revealed

that

large

portion

the

pavement

within

the

Greenbelt

National

Park

had

deteriorated

and

several

other

culverts

were

identified

deficient.

Also,

the

floodplain

the

Still

Creek

culverts

was

severely

constricted

from

approximately

250

feet

upstream

and

downstream

the

culvert

feet

the

culvert

crossing.

After

assessing

these

conditions,

was

decided

that

the

project

scope

should

include

the

following:

1. Floodplain	analysis	of	the	Still	Creek	crossing.
2. Pavement	rehabilitation	of	the	following	roads	and	parking	lots:

a. Route

b. Route

c. Park

Police

Substation

parking

area

(Rte.

0900)

d. Park

Headquarters

parking

area

(Rte.

0906)

e. Laurel

Picnic

area

access

road

(Rte.

0201)

and

the

Laurel

Picnic

parking

area

f. Holly

Picnic

Parking

area

(Rte.

0902)

g. Sweetgum

Picnic

Loop

(Rte.

0200)

and

the

Sweetgum

Picnic

parking

area

h. Dogwood

Natural

Trail

parking

area

(Rte.

0903)

3. Culvert	replacement	at	Sta.	201+64	on	Rte.	10
4. Culvert	replacement	at	Sta.	3+11	on	Rte.	11
5. Stormwater	management	(SWM)

3 Stormwater Management Report PRA‐GREE 11(1)

PROJECT

LOCATION

The

project

located

within

Greenbelt

National

Park

Prince

George’s

county,

MD.

Figures

and

show

vicinity

and

location

map

respectively.

FIGURE 1 – PROJECT VICINITY MAP

4 Stormwater Management Report PRA‐GREE 11(1)

FIGURE 2 – PROJECT LOCATION MAP

5 Stormwater Management Report PRA‐GREE 11(1)

ESD ALTERNATIVES ANALYSIS

The

strategy

Environmental

Site

Design,

ESD,

relies

integrating

site

design,

natural

hydrology,

and

smaller

controls

capture

and

treat

runoff.

The

following

summary

the

analysis

all

ESD

practices

and

their

suitability

for

implementation

this

project.

ALTERNATIVE SURFACES

A‐1.

GREEN

ROOFS

There

are

proposed

buildings

associated

with

this

project.

Therefore,

this

practice

was

not

considered.

The

project

linear

nature

and

involves

road

work.

A‐2.

PERMEABLE

PAVEMENTS

Percolation

test

did

not

yield

favorable

results

for

the

use

permeable

pavements

parking

lots.

Soil

predominant

throughout

the

project.

Therefore,

this

practice

was

not

considered.

A‐3.

REINFORCED

TURF

Most

reinforced

turf

has

lower

load

bearing

capacity

than

conventional

pavements.

Therefore,

applications

should

limited

locations

that

not

receive

heavy

vehicle

traffic

and

where

sub

soils

are

not

compacted.

Due

the

fact

that

the

parking

areas

this

project

are

heavily

used

and

the

loads

the

pavement

would

relatively

high

this

practice

not

considered

the

most

suitable

for

this

project.

NONSTRUCTURAL PRACTICES

B‐1.

DISCONNECTION

ROOF

This

practice

not

applicable

for

the

analysis;

roofs

present

the

project.

B‐2.	DISCONNECTION	OF	NON‐ROOFTOP	RUNOFF
This	practice	is	used.

Space

permeable,

vegetated

treatment

area

equal

the

minimum

flow

path

length

needed

for

treatment

must

available

down

gradient

the

impervious

cover

effectively

disconnect

runoff.

Topography

Runoff

must

conveyed

sheetlow

onto

and

across

open

areas

maintain

proper

disconnection.

The

disconnections

should

located

gradual

slopes

(<5%)

and

directed

away

from

buildings.

Hotspot Runoff

Disconnections

should

not

used

treat

hotspots

that

generate

higher

concentrations

hydrocarbons,

trace

metals,

toxicants

than

are

found

typical

stormwater

runoff

and

may

contaminate

groundwater.

The proposed use does not generate hotspot runoff.

6 Stormwater Management Report PRA‐GREE 11(1)

B‐3.

SHEETFLOW

CONSERVATION

AREAS

This

practice

not

applicable

because

evidence

recorded

legal

easement

could

not

provided

protect

the

conservation

areas

from

future

development

activities.

MICRO‐SCALE PRACTICES

M‐1.

RAINWATER

HARVESTING

This

practice

not

applicable

for

the

analysis;

rooftops

present

the

project

able

direct

flow

into

the

rain

barrels.

Also,

aesthetics

was

concern

due

the

pristine

nature

the

park.

M‐2.

SUBMERGED

GRAVEL

WETLANDS

This

practice

not

applicable

for

the

analysis;

Limited

project

space,

roadway

medians

present

the

project.

M‐3. LANDSCAPE INFILTRATION

This

practice

not

applicable

for

the

analysis;

Applicable

mostly

for

commercial

and

residential

land

uses

per

Chapter

Section

M‐3.

M‐4.

INFILTRATION

BERMS

This

practice

not

applicable

for

the

analysis;

Infiltration

berms

could

not

used

due

higher

slopes

along

the

roadway

and

also

due

the

absence

parallel

contours

along

the

road.

M‐5.

DRY

WELLS

This

practice

not

applicable

for

the

analysis;

Applicable

for

larger

sites

per

Chapter

Section

M‐5.

M‐6.

MICRO‐BIORETENTION

This

practice

not

applicable

for

the

analysis;

Not

enough

space

for

their

location;

also

ground

disturbance

had

kept

minimum

due

the

environmentally

sensitive

nature

the

project.

M‐7.

RAIN

GARDENS

This

practice

not

applicable

for

the

analysis;

Not

enough

space

for

their

location;

also

ground

disturbance

had

kept

minimum

due

the

environmentally

sensitive

nature

the

project.

M‐8.

SWALES

This

practice

not

applicable

for

the

analysis.

SWM

requirements

were

met

using

combination

disconnection

non‐rooftop

runoff

and

reduction

impervious

area.

M‐9.

ENHANCED

FILTERS

This

practice

not

applicable

for

the

analysis;

Enhanced

Filters

are

not

required

due

the

nature

this

project.

7 Stormwater Management Report PRA‐GREE 11(1)

TECHNICAL ANALYSIS AND DESIGN

HYDROLOGIC

ANALYSIS

The

Hydrology

for

SWM

was

based

the

methods

outlined

Maryland’s

Stormwater

Management

Guidelines

2010.

The

project

falls

primarily

under

the

redevelopment

category

and

rainfall

(PE)

inch

was

used

calculate

the

water

quality

volume

required

for

environmental

site

design

(ESDV).

Due

the

widening

the

road

the

proposed

bridge

approaches,

and

pavement

work

the

parking

lots,

there

will

increase

2,552

ft2

the

impervious

area,

requiring

treatment

under

the

new

development

criteria.

Per

table

5.3

the

MD’s

SWM

guidelines,

for

the

existing

soil

group

1.8

inches

was

used

calculate

the

ESDV

required

for

the

new

development

for

the

project.

The

calculations

for

the

hydrology

for

SWM

are

shown

the

subsequent

sections.

Please

refer

Appendix

A‐1

for

the

SWM

DAs.

The

ESDv

for

SWM

was

calculated

using

combination

redevelopment

and

new‐development

criteria

per

MD’s

guidelines.

Redevelopment

Per

MD’s

SWM

guidelines

2010,

the

existing

impervious

area

the

project

greater

than

40%

the

total

disturbed

area,

then

the

project

falls

under

redevelopment

requirements.

The

impervious

area

the

project

50%

and

ESDV

calculations

for

redevelopment

requirements

were

performed

follows.

TABLE 1 – EXISTING IMPERVIOUS AREA

Road/Parking Lot Area (sf) Type of Work

Main Entrance Rd. (Rt. 10) 527 Full Depth Reclamation

Park Central Rd. (Rt. 11) 23,740 Full Depth Reclamation

Bike Trail at Good Luck Rd. 2,006 Full Depth Reclamation

Good Luck Trail 29,975 Pavement Removal

Total (sf) 56,248

Existing Conditions

Existing Impervious Area (Refer to Table 1) = 56,248 square feet or 1.29 acres

Site Area = 2.59 acres

Imperviousness (I) = 1.29/2.59 = 50%

Since

40%,

under

redevelopment

conditions,

the

project

must

either

decrease

existing

imperviousness

within

the

LOD

50%

provide

water

quality

treatment

for

equivalent

area.

This

means

that

impervious

area

reduction

and/or

water

quality

treatment

shall

provided

for

50%

1.29

acres

0.65

acres.

8 Stormwater Management Report PRA‐GREE 11(1)

Proposed Conditions

Site Area = 2.60 acres

Proposed Impervious Area = 26,272 square feet or 0.60 acres

Impervious Area Reduction = 1.29 acres – 0.60 acres = 0.69 acres

Since

the

Impervious

area

reduction

0.69

acres

greater

than

the

required

impervious

area

reduction

0.65

acres,

this

satisfies

the

ESDv

requirements

for

the

Redevelopment

part

this

project.

New Development

Due

the

widening

the

roadway

the

proposed

bridge

the

Still

Creek

crossing,

new

impervious

area

being

added

the

project.

There

also

minor

increase

impervious

areas

the

parking

lots.

Refer

Table

for

summary

the

increase

impervious

areas.

The

amount

runoff

from

the

increase

imperviousness

will

reduced

level

equivalent

woods

good

condition

for

the

1‐year,

hour

rainfall

event.

The

calculations

for

ESDV

are

shown

below.

TABLE 2 – INCREASE IN IMPERVIOUS AREA

Road/Parking Lot Area (sf) Type of work

Rt. 11 Bridge & approaches 2,460 Full Depth Reconstruction

Sweetgum Parking 24 Full Depth New

Holly Parking 68 Full Depth New

Total (sf) 2,552

Increase in Impervious Area = 2,552 ft2 / 43560 sq.ft/ac = 0.06 acres

The

new

impervious

area

will

located

soils,

(Refer

Appendix

B‐4

for

the

Soil

Map),

therefore

according

Table

5.3

the

SWM

design

manual,

the

1.8

inches

for

0.06

acres.

ESDV = (PE)(Rv)(A)/12

Where, PE = 1.8 inch

RV = 0.05 + (0.009)(I); I = 100%

RV = 0.05 + (0.009 x 100) = 0.95

IART (A) = 0.06 acres

9 Stormwater Management Report PRA‐GREE 11(1)

ESDV = (1.8)(0.95)(0.06) x 43560/12

ESDV = 364 cu. ft.

ESDV = 364 cu.ft.

10 Stormwater Management Report PRA‐GREE 11(1)

HYDRAULIC	ANALYSIS
a. Disconnection	of	Non‐Rooftop	Runoff:

Per

Chapter

Section

N‐2,

Table

5.7

MD’s

SWM

guidelines,

disconnection

non‐rooftop

runoff

can

used

treat

inch

provided

the

length

disconnection

the

same

the

length

contributing

flow

from

impervious

area.

The

length

disconnection

must

between

ft.

and

ft.

Disconnection

non‐rooftop

runoff

being

proposed

separate

locations

for

the

project

site.

foot

wide

gravel

(No.

stone)

transition

strip

will

constructed

the

side

the

road

where

the

disconnection

located

order

ensure

that

runoff

will

flow

safe

and

non‐erosive

manner.

The

disconnection

will

directed

over

hydrologic

soil

groups

(HSG)

and

per

the

soil

map

obtained

from

Natural

Resources

Conservation

Survey’s

(NRCS)

Web

Soil

survey

database

(Appendix

–

2).

Table

provides

the

approximate

locations

the

disconnections

non‐rooftop

runoff,

along

with

their

respective

DAs

and

the

ESDVs.

The

total

impervious

area

being

treated

using

disconnection

non‐rooftop

runoff

5134

ft2.

Using

disconnection

non‐rooftop

runoff,

total

ESDV

428

ft3

will

provided.

This

will

satisfy

the

required

ESDV

364

ft3

and

the

required

IART

2,552

ft2

0.06

acres

These

locations

will

shown

the

final

construction

plans

along

with

their

respective

DAs.

Please

refer

Appendix

A‐1

for

the

locations

this

best

management

practice

(BMP).

TABLE 3 – DISCONNECTION OF NON‐ROOFTOP RUNOFF SUMMARY

STA DA (ft2) PE (IN) ESDv (ft3) Location Slope (%)

16+00 to 17+76 3654 1 305 LEFT 4.3

24+22 to 25+00 1480 1 123 LEFT 3.2

TOTAL 5134 428

11 Stormwater Management Report PRA‐GREE 11(1)

CONCLUSION

The

SWM

design

was

conducted

per

latest

requirements.

believe

that

using

combination

disconnection

non‐rooftop

runoff

and

reduction

impervious

area,

the

SWM

requirements

have

been

met.

the

same

time,

the

ground

disturbance

has

been

kept

minimum,

thus

providing

ESD

the

maximum

extent

possible

(MEP).

12 Stormwater Management Report PRA‐GREE 11(1)

APPENDICES

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