Advanced Topics: Solutions for Drainage Problemswater.rutgers.edu/.../RGWebsite/misc/Rusciano_DrainageProblems.pdf · Advanced Topics: Solutions for Drainage Problems Gregory Rusciano

Advanced Topics:Solutions for Drainage Problems

Gregory Rusciano

Program Associate, Water Resources

Rutgers Cooperative Extension

New Jersey Sea Grant Extension Program

Advanced Design Topics

Topics

• Dealing with clay soils

• Dealing with compacted soils

• Integrating rain gardens with sloped drainage channels and existing infrastructure


Dealing with clay soils…

1.Sizing considerations

2.Soil amendments

3.Under-drain systems

4.Overflow devices


Walk the property

What to look for…

• Identify areas of impervious cover

– Buildings/rooftops

– Paved areas

• Parking lots

• Driveways

• Sidewalks

• Identify semi-impervious areas

– Known areas of limited permeability

• Compacted soil

• High clay soils

• Identify sloped lawn areas


25

10

15

50

25

50

50' x 15' = 750 square feet

25' x 10' = 250 square feet

Total Area = 1,000 square feet

Driveway Area

One-Quarter of the Roof

25' x 12.5' = 312.5 square feet

HouseDriveway


Example in Sizing

Problem:

How big does a rain garden need to be to treat the

stormwater runoff from my driveway?


Example in Sizing

• Drainage Area = 1,000 square feet

• 1.25 inches of rain = 0.1 feet of rain

• 1,000 sq. ft. x 0.1 ft. = 100 cubic feet of water for the

design storm

• Let’s design a rain garden that is 6 inches deep

Answer:

10 ft wide x 20 ft long = 200 square feet

Check: 200 square feet x 0.5 ft deep = 100 cubic feet of

storage volume


Rain Garden Sizing Table

for NJ’s Water Quality Design StormArea of Impervious

Surface to be Treated (ft2)

Size of 6‖ deep Rain Garden

(ft2) or [w x d]


(ft2) or [w x d]

500 100 or 10’x10’ 50 or 10’x5’

750 150 or 15’x10’ 75 or 10’x7½’

1,000 200 or 20’x10’ 100 or 10’x10’

1,500 300 or 30’x10’ 150 or 15’x10’

2,000 400 or 20’x20’ 200 or 20’x10’


Sizing for Clay Soils

• Decrease the depth and increase the surface area

– (3—4‖ maximum depth)

– Provides more exposure to sunlight for evaporation

– Provides more pore spaces available for infiltration

– Provides more contact with mulch and plants (uptake)

• Depends upon available space on the property

• This will drive up your budget (additional plants and mulch)

• May lead to more maintenance (additional pruning weeding, etc.)


Water should be completely

drained within 24 hours.

Percolation Test

Ruler

1st Hour2nd Hour3rd Hour4th Hour


24 Hour Method

• Perform your percolation test

– 1.5 inches/hour is ideal (sandy/sandy loam)

• If water percolates completely within 24 hours…

– Still acceptable but decreasing the depth is advised

• If water does not percolate completely within 24 hours…

– Determine the 24-hour rate

– Use it as your maximum depth


Soil Amendments


Soil Test

• Sample the soil and send to the Rutgers Soil

Testing Lab for:

• Nutrient analysis/ recommendations

• pH analysis/ recommendations

• Percent sand/ silt/ clay

or textural class (then refer to fact sheet)

• Soil Texture Test

Roll soil into a ball in hand and see how it forms

• Hard ball – Clay/Silt soil

• Soft ball – Loamy soil

• No ball – Sandy soil

But, don’t worry – clay/silt and

sandy soils can be amended to get

the preferred loamy soil texture

Gloucester County 4-H Fairgrounds


Adding Amendments

• Compost and/or sand should be used

• Requires amending at least an additional six inches of the existing soil

• The clay soil that you remove can be reused for the berm


Digging Your Garden (3-8% Slope)


Adding Amendments

• Replace existing soil with sandy loam top soil or add a sand/compost mixture with a rototiller

(obtain bank run or concrete sand only)

• It will drive up the price

• You want the final soil mixture to be at least 50% sand content (refer to soil textural class triangle chart on Cornell fact sheet)


General Soil Amendments Amounts for a

100 sq ft Rain Garden (six inch depth)

Soil Amendment Amount for 100 sq ft Rain Garden

Sand 1 cubic yard

Compost 1 cubic yard

Fertilizer Follow Soil Test Result Recommendations

Lime Follow Soil Test Result Recommendations



Under-drainSystems


• Groundwater Recharge: Infiltrated water that is not

evapotranspired

• Groundwater shall not be recharged in areas with high

pollutant loading

• Waiver available for urban redevelopment

• Groundwater Criteria:

– Maintain existing (100%) average annual groundwater recharge

OR

– Infiltrate the increase in runoff volume for the 2-year storm

event

• No more than one foot between the rain garden

bottom and seasonably-high GW table

Groundwater Recharge


Rain Gardens/Bioretention Systems

NJDEP. 2004. NJ Stormwater BMP Manual.


Cross-Section of Rain Garden - Bioretention Basin

BASIN SLOPE

4 IN. MULCH LAYER

2.5 – 3 FT. PLANTING

SOIL BED (MIN.

PERMEABILITY 0.5 IN.

PER HOUR)

12 IN. SAND BED

12 IN. GRAVEL BED

4 IN. PERF. PVC PIPE

FILTER FABRIC

NATIVE PLANTINGS


Cross-Section of Rain Garden - Bioretention Basin

BASIN SLOPE

3 IN. MULCH LAYER

1 – 3 FT. PLANTING

SOIL BED (MIN.

PERMEABILITY 1 IN.

PER HOUR)

12 IN. GRAVEL BED

4 IN. PERF. PVC PIPE

FILTER FABRIC

NATIVE PLANTINGS


12” ponding depth

0 Hours

9” ponding depth

6 Hours

3” infiltration

6” ponding depth

12 Hours

6” infiltration

Bioretention Basin – Expected Infiltration


1 Day

2 Days

24” infiltration

3 Days

36” infiltration

No Standing Water

12” infiltration No Standing Water

No Standing Water

Bioretention Basin – Expected Infiltration


5-10 ft.

Outflow

Underdrain Pipe Schematic (plan view)

PVC Cap

PVC Cap

PVC Cap

Elbow

Elbow

Coupler

Pea gravel

Pea gravel

Pea gravel 5-10 ft.


Underdrain Cross Section

Discharge

point

Stone bed

Berm

Gradual pipe angle

6-inch deep ponding area

Existing slope

Underdrain pipe

can also

discharge to

existing

infrastructure

•Curb and gutter

•Catch basins

•Underground storm sewer pipe


OverflowOptions

•Alter the berm

•Utilize existing infrastructure


Berm Option

• Plant the berm with new plantings of grass plugs and mulch as necessary

• Reuse grass clumps or use sod or grass seed

• Use erosion control mesh blanket or burlap

• Overflow pathways

(depends on preference and erosion potential)– Sheet flow

– Pipe

– Berm notch lined with stone


Keep Your Rain Garden Level

Advanced Design TopicsFind the Slope of the Lawn

SlopeWidth

Height%100


Digging Your Garden (3-8% Slope)


Digging Your Garden (>8% Slope)




Leonard Park, Morris County

Overflow

Installation Steps


Utilizing Existing Infrastructure


Catch Basin Riser (cross section)

Six Inches

Rain garden

ponding areaRain garden

ponding area

Overflow


Using the catch basin with a berm

Ponding area

Ponding area

Berm


Sloped Lawns

Road

curb

Rain

garden

Advanced Design TopicsPlanning Steps

Site Visit

Determine Current Stormwater Flow

Union County Vocational School

Flow


Road

Swale Retrofit

curb


Compacted Soils

• Rototill before planting

• Remove and replace with sandy loam mixture

• Only use heavy equipment around the perimeter of the rain garden


Other Considerations in Dealing with Existing

Infrastructure


Walk the property

Stormwater conveyance…

• Rooftop gutters and downspouts (if any)

– Do they discharge above ground?

– Are they directly connected to the road?

– Are they directly connected to the underground storm sewer

• Existing stormwater infrastructure

– Curb/gutter in the parking lot or driveway

– Catch basins and storm sewers

• Look into the catch basins

• What is the direction of pipe flow?

– Open channel conveyance swales/ditches

– Detention basins

• Topography – flat vs. sloped

• Type of existing vegetation (if any)


Determine the various pathways of the stormwater runoff on the property

• Which of the pathways are ―impervious pathways?‖

• Where does the water ultimately go?

– A detention basin

– Nearby stream or lake

• Other signs that identify the pathways

– Erosion

– Patches of dead grass

– Areas of sedimentation

Ultimate goal: You need to determine a good place to “disconnect” the impervious pathway


Disconnecting the Impervious Pathway

• Try to install the rain garden as close to the source as possible

• Can the pathway be disconnected above ground?

• Does a ―cut‖ need to be made?

– Underground downspouts can be ―day-lighted‖ before discharging to the curb/gutter

– Curb cut before water enters the catch basin


Rain Garden Sizing Table

for NJ’s Water Quality Design StormArea of Impervious

Surface to be Treated (ft2)


(ft2) or [w x d]


(ft2) or [w x d]

500 100 or 10’x10’ 50 or 10’x5’

750 150 or 15’x10’ 75 or 10’x7½’

1,000 200 or 20’x10’ 100 or 10’x10’

1,500 300 or 30’x10’ 150 or 15’x10’

2,000 400 or 20’x20’ 200 or 20’x10’


Rooftop scenario

• Easiest scenario for estimating the drainage area

• Calculate the volume of water that discharges to the downspout

• If no gutters, follow the drip line with a ditch that conveys water into the rain garden

What if the gutters connect directly to the storm sewer system underground?


Hockman Farm, Winchester, Virginia

Roof

W

L1 L2

Surface Area = (L1xW) + (L2xW)

= (15’x20’) + (10’x20’)

= (300’) + (200’)

= 500 square feet

Roof

3. Measure Impervious Surface Area

Planning Steps

Site Visit


Rooftop scenario (cont.)

• Try to disconnect the downspouts before they enter the underground pipes

• Divert the water to an above ground rain garden using PVC pipe and fittings and/or corrugated plastic pipe

• If you cannot disconnect at the downspout try ―day-lighting‖ (if the underground pipe if it is near the surface of the lawn)

– Only attempt this if you are able to design the rain garden for the entire drainage area

– Be careful of more than one downspout connecting to the same underground pipe


Diverting the pathway

• You are changing the direction of flow

• Rain gardens are designed for 1.25 inches of rain

• Determine where the overflow would go for a storm larger than 1.25 inches

– Would diverting the water into a rain garden ADD to the problem?

– Take note of the down-slope infrastructure—can it handle the overflow in the event of a storm greater than 1.25 inches?

Next scenario…


Parking lot and driveways

• Estimating the drainage area can be difficult

• We often use surveying equipment for this

• What can you do?

– Obtain site plans and/or speak with the building manager

– Use the ―get wet‖ method—go out there in the rain.

• Consider…

– Parking lots and driveways are often pitched to convey water to one side or both sides (look for a slight ridge in the center)

– Sediment deposits along curbs are evidence of flow direction

– If there is not curb, dead grass patches and erosion are evidence of where the water leaves the asphalt

But even if you can accurately estimate the D.A. you might not be able to handle such a large rain garden project

Advanced Design TopicsPlanning Steps

Site Visit

1. Determine Current Stormwater Flow

Union County Vocational School

Flow


Dealing with curb cuts

• The goal is to divert the water into a rain garden before it enters the catch basin

• Make use of the existing infrastructure in the cases of overflow (above 1.25 inches of rain)

– The back end of the rain garden berm must not be lower then the elevation of the parking lot asphalt

– Reinforce the berm by making it wider/taller, if necessary.




Documents

Advanced Topics: Solutions for Drainage Problemswater.rutgers.edu/.../RGWebsite/misc/Rusciano_DrainageProblems.pdf · Advanced Topics: Solutions for Drainage Problems Gregory Rusciano