11.6.3 Resilience Features in the Water Supply System
In Mauritius, the water supply network consists of both surface water sources (rivers,
impounding reservoirs) and groundwater sources. A groundwater source requires
digging a borehole and then installing a submersible pump to pump the water into a
reservoir, sometimes followed by a booster pump as in Figure 9.1. With a simple
basic arrangement, one pump ran continuously for 17 years before it broke down.
When that happened, the Central Water Authority (CWA), Mauritius was lucky to
obtain and fix another submersible pump, after first removing the initial pump.
During the repair works (fortunately, only one day), water had to be supplied by
tanker lorries and other means. Over the years, the CWA has come up with several
approaches to increase the resilience of the water supply network, such as:
(a) Dig a second borehole
(b) Intensive pumping during heavy rains
(c) Install a standby generator in case of power breakdown
(d) Interconnect different networks
(a) Having a second borehole provides two advantages: (1) in Mauritius, ground
water levels in the aquifer do vary widely – as much as 20 metres – between the
dry and wet seasons. Therefore, the two pumps may be selected to operate more
efficiently, one at the dry season level, and the other at the wet season level, and
(2) should there be a pump breakdown as in the incident above or scheduled
maintenance works, an immediate relief is available with the second borehole,
even if the pump works less efficiently during a short time.
(b) Intensive pumping during heavy rains: Surface water is impounded within man
made reservoirs, which barely have a capacity beyond a year’s supply, unless
Table 11.16 Characteristics which influence resilience
Characteristic
Wrt
event
Reason
Robustness
Ex-ante In the retrofit or design stage, infrastructure resistance to
extreme events or impacts needs to be upgraded or increased.
Redundancy
Ex-ante In the retrofit or design stage, when options to increase robustness
may be more expensive than options to increase redundancy.
Reliability
Ex-ante In the retrofit or design stage, the infrastructure (pipes, pumps,
etc.) should be reliable under all conditions, even extreme events.
Resourcefulness
Ex-ante Prior to a hurricane, preparedness and organisation to restore
infrastructure service performance will increase resourcefulness.
Ex-post Resourcefulness will be subject to decisions taken to restore
infrastructure performance. (e.g., how available resources –
post-disaster – are distributed, and priorities established).
Rapidity (Response
and recovery)
Ex-ante Design changes, preparedness and organisation to restore infrastructure service performance, prior to a hurricane (event), will
increase rapidity.
Ex-post Rapidity will be subject to decisions taken to overcome disruption and to restore infrastructure performance (e.g., how available resources – post-disaster – are distributed, and priorities
established).
11.6 Case Study: Resilience in a Water Supply Network
327
In Mauritius, the water supply network consists of both surface water sources (rivers,
impounding reservoirs) and groundwater sources. A groundwater source requires
digging a borehole and then installing a submersible pump to pump the water into a
reservoir, sometimes followed by a booster pump as in Figure 9.1. With a simple
basic arrangement, one pump ran continuously for 17 years before it broke down.
When that happened, the Central Water Authority (CWA), Mauritius was lucky to
obtain and fix another submersible pump, after first removing the initial pump.
During the repair works (fortunately, only one day), water had to be supplied by
tanker lorries and other means. Over the years, the CWA has come up with several
approaches to increase the resilience of the water supply network, such as:
(a) Dig a second borehole
(b) Intensive pumping during heavy rains
(c) Install a standby generator in case of power breakdown
(d) Interconnect different networks
(a) Having a second borehole provides two advantages: (1) in Mauritius, ground
water levels in the aquifer do vary widely – as much as 20 metres – between the
dry and wet seasons. Therefore, the two pumps may be selected to operate more
efficiently, one at the dry season level, and the other at the wet season level, and
(2) should there be a pump breakdown as in the incident above or scheduled
maintenance works, an immediate relief is available with the second borehole,
even if the pump works less efficiently during a short time.
(b) Intensive pumping during heavy rains: Surface water is impounded within man
made reservoirs, which barely have a capacity beyond a year’s supply, unless
Table 11.16 Characteristics which influence resilience
Characteristic
Wrt
event
Reason
Robustness
Ex-ante In the retrofit or design stage, infrastructure resistance to
extreme events or impacts needs to be upgraded or increased.
Redundancy
Ex-ante In the retrofit or design stage, when options to increase robustness
may be more expensive than options to increase redundancy.
Reliability
Ex-ante In the retrofit or design stage, the infrastructure (pipes, pumps,
etc.) should be reliable under all conditions, even extreme events.
Resourcefulness
Ex-ante Prior to a hurricane, preparedness and organisation to restore
infrastructure service performance will increase resourcefulness.
Ex-post Resourcefulness will be subject to decisions taken to restore
infrastructure performance. (e.g., how available resources –
post-disaster – are distributed, and priorities established).
Rapidity (Response
and recovery)
Ex-ante Design changes, preparedness and organisation to restore infrastructure service performance, prior to a hurricane (event), will
increase rapidity.
Ex-post Rapidity will be subject to decisions taken to overcome disruption and to restore infrastructure performance (e.g., how available resources – post-disaster – are distributed, and priorities
established).
11.6 Case Study: Resilience in a Water Supply Network
327