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Extending the Service Life of Permeable Pavements Using Swales ...

Extending the Service Life of Permeable

Pavements Using Swales to Pre-treat

Stormwater

Kachchu Mohamed MA & Lucke T

School of Civil Engineering, University of the Sunshine Coast

Presented by Kachchu Mohamed

SIAQ Conference, Townsville, 2013


Extending the Service Life of Permeable

Pavements Using Swales to Pre-treat

Stormwater

Permeable Pavements & Clogging

Clogging Reduction Measures in PPs

Swales as Pre-treatment Systems

Objectives of the Swale Study

Field Experiment Methods

Results from the Swale Study

Conclusions

Continuation of the Study

SIAQ Conference, Townsville, 2013


Urbanization

Excessive runoff

Water quality issues

Permeable Pavement

WSUD Technology

Source control

Permeable pavements

SIAQ Conference, Townsville, 2013


Stormwater Management Benefits

Runoff reduction

Water quality improvement

Permeable Pavement

Clogging

SIAQ Conference, Townsville, 2013


Urbanization

Excessive Runoff

Water Quality Issues

Source Control

WSUD

Permeable Pavements

Incoming Sediments

Urban runoff sediments

Wash-off from impervious

surfaces

Sediment Properties

Sediment Concentration total

load

Particle Sizes (PSD)

SIAQ Conference, Townsville, 2013


Regular Maintenance

street sweeping, pressure washing

Removing/replacing top 10-20 mm of the bedding material

Using narrowly graded bedding material open graded

aggregate

Avoiding geo-textile layer in between bedding and base layers

Back flushing in porous pavements

SIAQ Conference, Townsville, 2013


Permeable pavements can be designed out by reducing the

erosion and sediment runoff onto the surface.

Proactive measure addition of a sediment pre-treatment

system upstream of permeable pavements will lower sediment

loads.

Incorporation of swales as pre-treatment systems in permeable

pavement treatment trains.

Swale

Permeable

pavement

Car park design with upstream

swale and permeable pavement

Impervious area

SIAQ Conference, Townsville, 2013


(a)

Permeable Pavement

Swale

(a) permeable pavement-swale system used in Rushton (1999)

average runoff volume reduction by 50% compared to impermeable pavements without a swale

at least 75% of pollutant reduction for TSS and metals compared to impermeable pavements

without a swale

(b)

Permeable

pavement

Bioretention

system

Impervious pavement

(b) impermeable pavement-permeable pavement-bioretention cell system used in

Brown et al. (2012)

Car park design with upstream

swale and permeable pavement

significant hydraulic improvements were observed

SIAQ Conference, Townsville, 2013


Swale

Permeable

pavement

Impervious area

Car park design with upstream swale and

permeable pavement

Swales and permeable pavements will be studied separately

A detailed investigation into runoff sediment removal

performances of swales

Set of controlled field experiments

SIAQ Conference, Townsville, 2013


Assess the sediment (total suspended solids-TSS) removal

performance of swales

Determine the sediment size fractions that are removed by

swales

Quantify the nutrient (total nitrogen-TN & total phosphorous-TP)

removal effectiveness of swales

Determine whether there is an optimum swale length for pretreating

runoff pollutants

SIAQ Conference, Townsville, 2013


Selection of field swales

Engineering Swale

University of the Sunshine Coast

Innovation Centre Swale

University of the Sunshine Coast

Sports Complex Swale

Caloundra (Sunshine Coast)

Swales with similar characteristics

length, grass

Minimum length of 30 m

cross section,

SIAQ Conference, Townsville, 2013


Simulating storm runoff

Testing under real storm events is extremely difficult

Simulation is reliable and simpler to undertake/controllable

Inlet flow rate to represent a 1 year 25 min duration ARI storm

Approximate constant inlet velocity of 1.6 L/s 2000 L of volume

Adding synthetic pollutant constituents to replicate runoff

pollutants

key pollutants in this study

TSS, TN & TP

SIAQ Conference, Townsville, 2013


Experiment runs at 4 different pollutant constituents

concentrations

Pollutants

Concentrations (mg/L)

Test

A

(Control)

B

(x1)

C

(x5)

D

(x10)

Total suspended solid (TSS) - Silica - 150 750 1500

Total nitrogen (TN) - KNO 3 - 1 5 10

Total phosphorous (TP) - KH 2 PO 4 - 1 5 10

Test-A was a controlled test without addition of any pollutants

Test-B represents the typical Australian runoff quality

Silica to simulate TSS was selected from a variety of available silica by

choosing the proper PSD that matching with urban runoff sediments

Chemical reagents were used to represent TN & TP in the stormwater

SIAQ Conference, Townsville, 2013


Tank (2000 L) was filled for every test run

A submersible pump with special fittings was used as the mixer inside the tank

pump stirred the water for 10-15 mins before the test run begins

deliver stormwater into the swale at equal concentration with time and

water level from the tank

SIAQ Conference, Townsville, 2013


After thorough mixing, tank outlet was opened and water left into the swale

Flow into the swale took place for 21 mins at approximately 1.6 L/s rate

Grab samples were collected at every 5 m along the swale

Three samples at each collection point to form time composite samples

Samples were analysed at laboratory for TSS, TN & TP

(APHA/AWWA/WPCF)

SIAQ Conference, Townsville, 2013


Total Suspended Solids (TSS)

Removal

Test-A: Background concentrations

showed quite low values (


On average, 50-85% of the TSS

was removed by the swales

The percentage reduction of TSS

found to increase with higher

inlet concentrations

TSS concentrations reduced exponentially along the length of the swale

About 75% of the TSS concentration fall steeply at the first 10-15 m of

the swale

SIAQ Conference, Townsville, 2013


Rapid removal of TSS in the first 10-15 m of the swales

shows that excessively long swales to pre-treat runoff may

not be the most effective solution

Removing about 75% of the TSS could significantly reduce

the incoming sediments onto PPs

Accommodating short (10-15 m long) swales in car parks

can be an effective way to reduce/delay clogging in PP car

park designs

SIAQ Conference, Townsville, 2013


Nutrient Removal (TP )

Swales were only of limited effectiveness in removing TP from synthetic

stormwater at lower concentration runs

Notable reduction was found at higher concentrated runs (Test-C & D)

Negative removal of TP was observed in Test-A

SIAQ Conference, Townsville, 2013


Nutrient Removal (TN)

Swales were only of very limited effectiveness in removing TN from synthetic

stormwater

TN removal was negative in Test-A & B, Test-C & D was found to be neutral

SIAQ Conference, Townsville, 2013


Pollutant Removal

TSS removal was consistent with previous research

findings

Nutrient removal was varying and not in agreement with

previous research results

Could be caused because of the fully soluble

chemicals used

A significant proportion of nutrients are attached to the

sediments in real runoff conditions

Residence time may have influenced the nutrient

removal

Hydraulic benefits

Inlet flow into the swale was maintained for about 21

minutes, however outlet flow from the swale continued for

a minimum of 90 minutes

Flow attenuation/residence time

SIAQ Conference, Townsville, 2013


The study investigates the potential of swales as pre-treatment

for permeable pavements to reduce clogging

Field study at three different swales has shown high TSS removal

by the swales (50-85% removal)

The first 10-15 m stretch of the swales removes about 75% of the

TSS concentration rapidly, and the removal rates after this

stretch slow down

SIAQ Conference, Townsville, 2013


Results suggest short swales (10-15 m) can be accommodated in

WSUD car park designs, upstream of permeable pavements to

reduce clogging

Swale-permeable pavement treatment trains have the potential

to increase effective life span of permeable pavement while

improving the overall stormwater management benefits

Swales perform satisfactorily to remove runoff nutrients at very

high concentration events

SIAQ Conference, Townsville, 2013


A complete analysis of inlet and outlet swale runoff

samples for sediment PSD

Size fraction removed by the swales

Laboratory pavement models will be tested under swale

pre-treated runoff condition

Test with typical runoff sediments

Test with swale treated runoff

Reduced concentrations

Modified PSD of sediments

Clogging

Experiment

Set-up

SIAQ Conference, Townsville, 2013


Humes Water Solutions, Australia

Mr. Graham Bebington, Sunshine Coast Council

Mr. Hugh Allan & Mr. Bernard Black, USC Lab Technicians

Mr. Liam Owen, USC, Honours Student

SIAQ Conference, Townsville, 2013

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