Knowledge Exchange mission SUSWA project 30 November – 5 December 2014, Kajiado, Kenya...
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Transcript of Knowledge Exchange mission SUSWA project 30 November – 5 December 2014, Kajiado, Kenya...
Rainwater harvesting and artificial groundwater recharge to improve
Kwemakame Spring Yields
Harry Rolf SamSamwater
27/10/2014
Kwemakame project history• Chamavita, Mr. Kempenaar and mama Els• 1989 scheme construction
– 10 intakes– 2500 - 3500 users
• 2004 ‘depletion’>Tsedaka>AquaforAll>Chamavita• 2006 practicalresearch project
– Cause of depletion?– How to improve?
project history (2)
• 2006 – 2010 • Monitoring• Field investigations • Analysis
• 2009 understanding > strategy>pilots
• 2010/2012 pilot design & construction
• 2013 ‘post-pilot’ monitoring and reporting
• 2014 dissemination
Partner ProjectLocal Partners:• Village Kemakame/Kai
• Chamavita (Chama cha maendaleo vijijini tanga)
• Pangani Basin Water Office
The Netherlands:• AquaforAll (funding)• Aquanet (funding)• PWN/SamSamWater (techn.
Assistance)• SPOT Tanzania
Kwemakame/Kwai
Estimated 3000 people• Kwai/Kwemamake Water Board• 9 sub-villages/hamlets each having
water committee• 34 tap watercommitees
Water demand 1 liter/sec
Scheme constructed 1989, but the yield dropped since the initiation
Present Water sources (dry season):• Dindira ‘spring’ catchment (0,35 l/sec)• Kidandi ‘spring’catchment (0,15 l/sec)
Total yield Dindira
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
01/0
1/1
1
01/0
3/1
1
01/0
5/1
1
01/0
7/1
1
01/0
9/1
1
01/1
1/1
1
01/0
1/1
2
01/0
3/1
2
01/0
5/1
2
01/0
7/1
2
01/0
9/1
2
01/1
1/1
2
01/0
1/1
3
01/0
3/1
3
01/0
5/1
3
01/0
7/1
3
01/0
9/1
3
01/1
1/1
3
dis
ch
arg
e in
l/s
ec
tot flow monthly avg
estimated demand (including animals)
domestic only
Kidandi source
project result
Gravity spring captation
Impervious base
Rainfall and evapotranspiration
Recharge
runoff
spring
spring
‘spring’ wall intake
Water scheme
ch. 6
chamber 5
intake 8 intake 9
intake 10
intake 11
chamber 2
other intakes
storage tank to Kwemakame
From 11 intakes to 5 collection chambers
From collection chambers to storage tank
From storage tank down to village distribution
Research methodology
• Monitoring (Rainfall, evaporation, yields,…)
• Field reconnaisance
• Mapping
• Analysis/ understanding
Field investigations
• GPS mapping
• Geophysical sounding and profiling
• Augering
• Infiltration capacity testing
• Water chemistry & temperature
AnalysisWenner profile Dindira (Kwemakame) intake nr.2 sub-catchment
1940
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
-10 -7.5 -5 -2.5 0 2.5 7.5 10 12.5 17.5 20 22.5 27.5 30 32.5 37.5 40 42.5 47.5 50 52.5 57.5 60 62.5 67.5
distance from centre (m)
alti
tud
e (m
)
100
1000
10000
app
aren
t re
sist
ance
(o
hm
-m)
groundsurface (waypoints)
ground surface (interpret)
apparent res (Ωm) 3x5m
apparent res (Ωm) 3x10m
outcrop
Aquifer properties
Cumulative rainfall
0
200
400
600
800
1000
1200
Nov Dec J an Feb March April May J une J uly August Sept Oct
tota
lrain
fall
(mm
)
Dindira 2007/2008
Dindira 2008/2009
Normal Rainfall (New LocClim)Normal rainfall Lushoto
Dindira 2009/2010
Rainfall analysis
Kwemakame total discharge
0
10
20
30
40
50
60
jan/0
8
mrt
/08
mei/08
jul/08
sep/0
8
nov/0
8
jan/0
9m
rt/0
9
mei/09
jul/09
sep/0
9
nov/0
9
jan/1
0m
rt/1
0
mei/10
jul/10
sep/1
0
rain
fall
(m
m/d
ay)
0
0.5
1
1.5
2
2.5
3
3.5
dis
ch
arg
e (
l/sec)
rainfall (mm
flow in ch 5
27/10/06 chamber 5
Rainfall discharge relationship
Reasons for depletion
• Over decades: springs dried up due to deforestation.
• Rapid population increase• Climate change? (no proof)• Since 1989: yield decreased because of using up
groundwater storage
Reasons for depletion (2)Just too little recharge
Most of the water is running off , being lost out of the area
Intakes are just ‘scraping’ the recharge added in the last rain season
Groundwater dropping
Key to improvement
INCREASE THE AMOUNT OF WATER THAT INFILTRATES INTO THE GROUND
Water is available:
A lot of water in running off unutilized
Strategy options
• Plant trees (yes, good solution but on the long run)
• (Let it rain more)
• (Pump water)
• (Deeper intake wall)
• (Surface water storage and treatment)
• Add water in the underground:– ‘artificial recharge’
Strategy to improve
Artificial Recharge:– Harvest rainwater that is running of– Temporary storage– Infiltration in the underground– ‘boost’ groundwater > increase yield
3R
Retention
Recharge
Re-use
Results
A total amount of 2,5 million liters has been infiltrated
This water is added to groundwater and slowly flows down to intake, flowing out in the dry season
Some intakes were closed. By doing that, groundwater is conserved for the dry season. This has been beneficial as well.
2013 dry season effect:The people from Kwemakame/Kwai noticed considerably more water.
“we don’t know exactly what you’ve been doing up there in Dindira, but it helped a lot. We didn’t experience having so much water for many years. Even in the last dry months we had water all day long”.
Dry season yield monitoring
year month yield (l/sec)2009 Oktober 0.152010 November 0.422011 September 0.312012 November 0.25-------------------------------------------------
average before the project: 0.302013 November 0.702014 29/10/2014 0.90
Observed yield of the Dindira Water Catchment at the end of the dry season
•Yield increased from 0.30 to 0.80 l/sec
•Kwemakame/Kwai requires is 1.0 l/sec•Kidandi source gives 0.15• The required water is now available
CONCLUSIONS• Rainwater harvesting and infiltration by
artificial recharge can significantly improve the water supply
• Water conservation by closing intakes during the rain season adds a positive effect as well.
• Proper maintenance and operation is a first requirement for sustainability
• The community, Chamavita and Pangani Basin Water were deeply involved in this project and gained a lot of new knowledge on how to improve the ‘spring’ water catchment system. They are eager to replicate and upscale the concept to similar water schemes.
CHALLENGES AND LESSONS LEARNED• Assessment of runoff (where, how much)• Proper operation and maintenance is crucial • Re-use Silts that are trapped in the dam• Construction of earth dams on steep slopes.• To replicate this in other areas, you first need to understand the groundwater
system• For this understanding hydrological monitoring is required (yields, groundwater levels,
rainfall,…) •
Other (technical) lessons learned.• It is extremely difficult to manage extensive hydrological monitoring without experts on the
ground, who are continuously analysing and checking the quality of the data collection.• Know your runoff in the early project stages. It is important to know how much runoff water
is there to catch. In our case the runoff was less than expected. Runoff tracks must be identified (and quantified) beforehand during heavy rains.
• Rainfall variability is high. For quantification purposes it is essential to have multiple rain stations over the catchment, measuring not only daily totals but rainfall intensity as well.
• The results show that rationing is effective, saving additional water for the dry season. In particular think of closing the highest intakes during the rain season ( starting with nr.2)
• How much and how fast will the infiltration water flow out at the source/intake: a set of ‘design rules’ is required.
• Proper operation and maintenance of the facility and its surroundings is required to assure that it will continue supplying.
Other (technical) lessons learned.• It is extremely difficult to manage extensive hydrological monitoring
without experts on the ground, who are continuously analysing and checking the quality of the data collection.
• Know your runoff in the early project stages. It is important to know how much runoff water is there to catch. In our case the runoff was less than expected. Runoff tracks must be identified (and quantified) beforehand during heavy rains.
• Rainfall variability is high. For quantification purposes it is essential to have multiple rain stations over the catchment, measuring not only daily totals but rainfall intensity as well.
• The results show that rationing is effective, saving additional water for the dry season. In particular think of closing the highest intakes during the rain season ( starting with nr.2)
• How much and how fast will the infiltration water flow out at the source/intake: a set of ‘design rules’ is required.
• Proper operation and maintenance of the facility and its surroundings is required to assure that it will continue supplying.
Water quality• Indication of raised Nitrate contents by
agriculture • Water source protection must be addressed• Artificial recharge preferably in the forest area,
lakini….
• Unfortunately the new intake has much less water than expected
• Permanent Groundwater seepage flow to the dam 5000 lita every day!
• This water is treated by a SSF (Slow Sand Filter)
• Very unfortunately the new intake has much less water than expected due to bad siting (by us).
• The aquifer is largely blocked by clays
• In stead the water is seeping to the reservoir (4000 l/day)
• Water is treated by a Slow Sand Filter