EWRI: Kelly Doyle's Presentaiton- The Impact of First Flush Removal on Rainwater Quality and...

www.ma-rs.org Montgomery Associates

Resource Solutions, LLC

The Impact of First Flush Removal on Rainwater Quality and Rainwater Harvesting Systems’

Reliability in Rural Rwanda

Kelly C. Doyle – Montgomery Associates: Resource

Solutions

Dr. Peter Shanahan – Massachusetts Institute of

Technology

May 17, 2010



Outline• Project context

• Intro to first flush (FF)

• Fieldwork

• Storage-Reliability-Yield (SRY) simulation

• Effects of FF on SRY



Project Details• Project Location

– Bisate Village, Rwanda

• Project Partner– Dian Fossey Gorilla

Fund International

African Conservation Foundation



Project Context

Problem:• 95-99% of the population

infected with worms• Inadequate water supply

(volume)• Contaminated water

supply

Approach:• Rainwater harvesting

(water supply)• First flush diversion

(treatment)



Average Monthly Rainfall Distribution

71

89

135

172

148

38

17

50

124

164

151

84

0

20

40

60

80

100

120

140

160

180

200

Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.

Ra

infa

ll D

ep

th (

mm

)

R

ainf

all D

epth

(m

m)



Rainwater Tanks 2007



The Clinic- 41.35 m3

Trackers’ House-42.5 m3

Primary School-40 m3

People Served:- 20,000 people

served- 100 patients per

day- 15 patient beds

People Served:- 1,700 students

People Served:- 50 trackers

Rainwater Tanks 2008



The first portion of the total discharged storm volume which contains the main proportion of the pollutant load during a storm event

(Bertrand-Krajewski et al. 1998)

What is the First Flush?



Constant Volume Diverter

Storage tank

Gutters

Diversion pipe

Removable cap

Tank inlet

Courtesy of Matt Stevenson



Research Questions

• How much first flush to

divert?

• How is reliability affected?



The GIZMOGraduated Inflow-collector for Zero Mixing

with Overflow



New Clinic Roof (CL)

First setup: 0.66 mm rain

Second setup: 1.34 mm rain

Roof material: new iron sheetsLocation: close proximity to

road



Rusty Roof House (HS)

Roof material: old, rusty iron sheets

Location: far from vehicle road

Captures first 1.45 mm of rain



Potato House (PT)

Roof material: old clay tilesLocation: moderate distance

from vehicle road

Captures first 1.61 mm of rain



Water Quality• Membrane filtration

– Total Coliform– E. coli

• Turbidity• pH• Conductivity



y = 0.93e-4.25x

R2 = 0.79

y = 1.55e-1.70x

R2 = 0.98

y = 1.31e-1.75x

R2 = 0.93

y = 1.35e-1.73x

R2 = 0.93

y = 1.37e-1.36x

R2 = 1.00

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

Runoff (mm)

cu

mu

lati

ve

rela

tiv

e r

ed

uct

ion

(1s

t al

iqu

ot=

1)

S1

S3

S4

S5

S6

** Note: Storm S1 had a different array setup than subsequent storms

Storm Trendline Event Eq'n

Turbidity Reduction Trends-CL



Turbidity Reduction Trends-HS

y = 1.39e-1.26x

R2 = 0.88

y = 0.58e-1.18x

R2 = 0.36

y = 1.27e-1.52x

R2 = 0.95

y = 1.77e-2.02x

R2 = 0.90

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

Runoff (mm)

cu

mu

lati

ve

rela

tive

re

du

cti

on

(1s

t al

iqu

ot=

1)

S1

S3

S5

S6

** Note: Storm S4 was not included for clarity. See discussion regarding outliers.

Storm Trendline Event Eq'n



Turbidity Reduction Trends-PT

y = 1.30e-1.04x

R2 = 0.99

y = 0.99e-0.79x

R2 = 0.82

y = 1.17e-0.63x

R2 = 0.95

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

Runoff (mm)

cum

ula

tive

rel

ativ

e re

du

ctio

n (

1st

aliq

uo

t=1)

S3

S4

S6

Storm TrendlineEvent Eq'n



Previous Work

• Martinson and Thomas 2005– Uganda– – k range 0.65 – 2.2

• Doyle 2008– Rwanda– k range 0.63 – 2.0

(without outliers)

krteNN 0



0

20

40

60

80

100

120

0.0 0.5 1.0 1.5 2.0Runoff (mm)

Raw

Tu

rbid

ity

(NT

U)

CLHSPT

** Note: The turbidity value at CL-S1 was removed to make the graph more readable; the value was 893 NTU.

Sample Location

Recommendation to divert 1st mm of runoff:

Turbidity reduction



Storage-Reliability-Yield (SRY)Simulation Model

n

dq f1

q = time-based reliability

df = # days demand is not met

n = total days in study



SRY Simulation Results

15% losses, no FF diversion

15% losses, 1 mm diversion after 3 consecutive days each with < 1mm rain

X X

S

tora

ge (

m)

S

tora

ge (

m)

Yield Yield



Effect of FF Diversion on Reliabilityin Bisate

Reliability (%)

ScenarioHealth Clinic

Primary School

Trackers’ House

15% losses, no diversion 92% 31% 89%

15% losses, 1 mm diversion after three consecutive days each with <1 mm rain

91% 30% 87%

Reduction in reliability from diversion scheme

1.5% 1.0% 1.7%

Additional days not meeting demand with first flush diversion

6 days 4 days 7 days



Conclusions• 1 mm diversion of runoff• Small reduction in reliability (<2%)• 50% reduction in turbidity• Reduced coliform and E. coli

Rainwater from the gutters

Diverted first flush

Removal cap to empty pipe

with chainSoak-away

pit

Cleaner water to main tank



Murakoze Cyane!

• Pete Shanahan• John Peter

Nshimyimana• Bernard Isaacson• DFGFI• MIT PSC• Montgomery

Associates



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