Our Dry Weather Plan South East Water's 2021 draft drought plan - Appendix Q - Drought Plan Testing - South East Water Corporate

Our Dry Weather Plan
South East Water’s 2021 draft
drought plan – Appendix Q -
Drought Plan Testing

March 2021

South East Water
Rocfort Road
Snodland
Kent
ME6 5AH

Drought Plan | March 2021

Contents

1 Testing the plan 3
1.1 Testing against drought scenarios 5
1.1.1 Short-term drought (2003) 5
1.1.2 Medium duration, multi season drought (1995-1997) 10
1.1.3 Long term drought (2003-2006) 16
1.1.4 Two dry winter drought (2010-2012) 22
1.1.5 Overall findings from the historic scenarios 27
1.1.6 Historic scenario testing conclusion 28
1.2 Testing against a range of alternative drought scenarios 29
1.2.1 Summary of worst historic, severe and extreme drought scenarios 41
1.3 Testing against a third dry winter drought scenario 44
1.4 Conclusions and linkages with our water resources management plan 47

Appendix A Drought scenarios tested 49
A.1 Stochastic drought scenarios 49
A.2 Third Dry Winter scenario 79

The content of this appendix is unchanged from the 2019 Drought Plan Section 8 and
Appendix T.

Author: South East Water | March 2021 Page 2 of 96

Drought Plan
 March 2021

1 Testing the plan
The Defra and the Environment Agency updated guidelines require companies to test
their plans against a range of plausible droughts to demonstrate their flexibility and
robustness. The guidelines state that:

‘Your plan should include how you’ll deal with a range of droughts including both long
duration and very low rainfall relative to expected conditions in your water resource
zones (WRZs). You should at least plan to be able to provide supplies through a repeat
of historic droughts in your company records. However, we strongly encourage you to
plan for drought events that are of longer duration and lower rainfall than those in the
historic record, or if not you should explain why. You should understand what drought
events your supply system is vulnerable to and what the probability of such an event
occurring is.’

To satisfy this requirement, we have tested our plan against a range of observed
historic (including the worst historic drought, 2010-2012) and stochastically generated
droughts that are different in terms of severity, duration and hence impacts. The
approach was to test our triggers and drought status classification system against
these droughts and demonstrate how our drought management actions would be
implemented in each case. The trigger curves for our two reservoirs are updated for
this drought plan to ensure consistency with our WRMP19.

Wherever possible, we have assigned a return period to the drought event for the
scenarios we have presented. A return period is terminology used to analogise the
likely frequency of occurrence of an event. Return periods can also, perhaps more
helpfully in this instance, be viewed in terms of a probability of occurrence in any one
year. For example, classifying a drought in terms of having a one in 100 year return
period means there is a one per cent probability that a drought of that magnitude could
be experienced in any one year. Similarly, a one in 200 year drought has a 0.5 per
cent probability of occurring in any one year.

We have selected the following historic drought scenarios as the most appropriate
droughts to use:

 Short-term drought (2003) characterised by high demand triggered by hot dry
 summer, but with relatively high groundwater conditions;
 Medium duration, multi season drought (1995-1997) characterised by
 sequential years of hot dry weather with below average recharge;
 Long term drought (2003-2006) characterised by sequential years of below
 average recharge and high forecast demands; and
 Two dry winter drought (2010-2012) characterised as the name suggests by two
 consecutive dry winters resulting in very low groundwater levels.

Although the 1995–1997 and 2003–2006 scenarios have the same period of duration,
the 1995–1997 presents alternating patterns of drought severity between the different
drought regions, whereas 2003–2006 represents a more ‘uniform’ long term drought.
The 2010-2012 drought has been illustrated using modelled operation of our two
reservoirs (Ardingly and Arlington) in response to observed rainfall-runoff sequences
during that drought event, as opposed to observed storage level data. This is because

 PAGE 3

Drought Plan
 March 2021

our two reservoirs were operated abnormally during this period and hence using
observed storage levels would be misleading and inappropriate. Alternative drought
examples for the short, medium and long-term drought scenarios were also
considered; however, due to a lack of available data for some drought regions, 2003
has been used as the short-term example scenario as well as the starting year of the
long-term drought example scenario.

In addition to the assessment of historic droughts, we have developed alternative
drought sequences using a stochastic approach. A wide range of droughts were
selected for testing, representing varying severity and duration:

 Three stochastic worst historic droughts: characterised the probability of
 occurring once in 100 years on average (1 per cent chance of occurring in a given
 year), and by having a similar severity to the observed worst historic drought. The
 three droughts have varying durations of 12, 18 and 24 months
 Three stochastic severe droughts: characterised the probability of occurring
 once in 200 years on average (0.5 per cent chance of occurring in a year), and by
 having a higher severity to the observed worst historic drought. The three droughts
 have varying durations of 12, 18 and 24 months
 Three stochastic extreme droughts: characterised the probability of occurring
 once in 500 years on average (0.2 per cent chance of occurring in a year), and by
 having a much higher severity to the observed worst historic drought. The three
 droughts have varying durations of 12, 18 and 24 months

To test our plan further, and understand its performance under a prolonged drought,
we have developed a third dry winter drought scenario. We have adopted a ‘what if’
approach and extended the 2010-2012 drought to continue onto a third dry winter.

At the end of each scenario, we have provided a brief explanation of the extent to
which drought triggers and actions taken may be impacted by the triggering of the
bulk supply override triggers described in section Error! Reference source not
ound..

This involved applying all the bulk supply override triggers in each month of the drought
scenarios we have tested to see what effect this might have on our drought action
response. When assuming the override trigger has occurred it has been given a level
three severe drought score, and the bulk supply yield is assumed to align with one in
500 year drought yields (see Error! Reference source not found.). We have then
bserved what effect the introduction of the override trigger has had on the overall
drought status each month during the drought. This has been done in the context that
we would not likely lose the whole output from the bulk supply, just a portion of it (as
per the values stated in Error! Reference source not found.), and that bulk supplies
nly provide between seven per cent and 11 per cent of the total supply across our
drought regions.

The overall purpose of this scenario testing section is to demonstrate our response
and show the effectiveness of our plan to the range of selected droughts.

 PAGE 4

Drought Plan
 March 2021

Since our plan will be tested against our drought triggers a distinction has to be made
between the severe drought status defined by the breach of our monitoring triggers
(described in Section 3) and the severe drought events we have generated to test the
system. For the purpose of clarity, the following terms will be used in this section:

 1. ‘Severe drought status’: This refers to the fourth stage of drought
 development (as defined by the Environment Agency) determined by
 monitoring the breach of a combination of drought triggers as described in
 Chapter 2. Severe drought status would enact a specific set of operational,
 management, communication and environmental actions.

 2. ‘Severe drought impact’: This refers to the stochastically generated plausible
 drought event that has a modelled severe impact on our system and with a
 probability of occurring once every 200 years. This definition is in line with
 industry guidance.

1.1 Testing against drought scenarios

The guidance suggests that the selected historic drought scenarios should include
current water resource infrastructure, demands and operations. The demand
sequence selected for the modelling of all scenarios is January to December 2003
(because it presents a realistic worst-case scenario). Error! Reference source not
ound. shows graphs of the 2003 demands for each of the three drought regions.

The historically observed drought scenarios are presented and analysed in the
following sub-sections. The four scenarios were tested on all three drought regions, to
examine response across our whole area.

Overall the drought scenarios affect the three drought regions at different times and
with differing magnitudes. We have ensured that the scenarios used lead to each
drought region moving from one drought status to another, and thus triggering
drought actions. A selection of the 2003–2006 groundwater, recharge, and reservoir
storage curves for each of the drought regions are shown in Error! Reference
ource not found..

1.1.1 Short-term drought (2003)
2003 has been selected as an illustration of the situation when demands were
exceptionally high in mid-summer, but the groundwater resources were generally
sufficient. The 2003 scenario is considered to have a greater than one per cent
probability of occurrence in any given year, i.e. a return period of greater than one in
100 years. The 2003 scenario also forms part of the 2003-2006 long term drought
scenario, see Section 1.1.3.

For each month of 2003 the trigger scores were collated and entered into the drought
assessment matrices. To demonstrate the workings of the initial and overall trigger
matrices, September 2003 is presented in Table 1.1 and Table 1.2.

The month of September indicates that overall (see Table 1.2) Eastern (1-3) was at a
moderate drought status and Eastern (6-8) and Western (4-5) were at developing

 PAGE 5

Drought Plan
 March 2021

drought status. The reservoirs in Eastern (1-3) (see Table 1.1) were extremely low,
indicating a moderate / severe drought. Recharge and demand triggers across our
area were indicating a developing to moderate drought.

 PAGE 6

Drought Plan
 March 2021

Table 1.1 – Initial trigger matrix for September 2003 scenario
 Groundwater Surface Water Recharge Demand
 Elphicks Farm Trial
 1 Ardingly 2 Goudhurst (Ashdown Beds) (32%) 1
East (1-3)

 (Ashdown Beds) (32%)
 Cornish (Chalk S Downs) Poverty Bottom (Chalk South
 (44%)
 0
 Downs) (44%)
 2 East (1-3) 2
 Ryarsh (Gs W of Medway)
 Arlington 3 Cramptons (Greensand West of
 (20%)
 1 Medway) (20%)
 2
 Hambledon Old Schl (Gs
 0 Cleve (Chalk Maidenhead) (25%) 1
West (4-6)

 Wy+Lod) (37%)
 Stonor Park (Maidenhead Basingstoke (East Hants Downs)
 Chalk) (25%)
 1 n/a (38%)
 1 West (4-6) 1
 Winslade Farm (E Hants Borden (Wey Loddon Greensand
 Downs) (38%)
 0 and HB) (37%)
 1
 Charing No 7 (Gs E of
 Medway) (23%)
 1 Goudhurst (Ashdown Beds) (5%) 1
 Dane Court (Chalk Stour) Cramptons (Greensand West of
 (43%)
 0 Medway) (7%)
 2
 Duckpit Farm (Chalk N Boughton (Chalk North Downs)
 0 n/a 2 East (7-8) 2
East (7-8)

 Downs) (22%) (22%)
 Elphicks (Ashdown Beds) Charing (Greensand East of
 (5%)
 0 Medway) (23%)
 2
 Ryarsh (Gs W of Medway)
 (7%)
 1 Boughton (Chalk Stour) (43%) 2
 Key: (0) normal drought status, (1) developing drought status, (2) moderate drought
 status, (3) severe drought status.

Applying the override trigger during September 2003 (the time period reflected in Table
8.1), i.e. escalating our drought status to take account of a reduction in bulk supply
volume from a neighbouring company, would not alter the overall scores much at a
drought region level. Although it would likely move the status of our groundwater
triggers from developing to moderate drought, our overall regional assessment is
already likely to be at moderate drought due to the combined status of our surface
water, recharge and demand triggers. Therefore, if another company hit its triggers
then it would escalate our drought management actions such that we plan for the loss
of some/all of a neighbouring water company’s bulk supply earlier. In this way, we see
the true benefit of the override trigger and how it would have worked really well in
practice.

To help determine the drought status for each drought region the trigger schematic tool
was used to help compare the balance between the current and predicted resources
and demand. Figure 1.1 plots selected drought months for a selected drought region
throughout 2003 and shows the progression of the drought in terms of the increase in
demands through to August and the falling resources throughout the year until
October, when the resources situation begins to improve. The grey arrows help to
indicate this trend.

 PAGE 7

Drought Plan
 March 2021

Table 1.2 – Overall trigger matrix for September 2003 scenario
 Company Trigger Trigger 2 Trigger 3 Trigger 4 Override Comment Overall
 Drought 1 Trigger drought
 Region region
 Resources Status Recharge Demand/ Bulk score
 Forecast supplies
 GW Reservoirs demand / Shared
 sources

 Moderate Drought - 2

 Reservoir levels extremely
 Eastern
 1 2-3 2 2 0 low, with groundwater 2
 (1-3)
 levels falling. Recharge
 forecasts are low and
 demand remains high.

 Developing Drought - 1
 Western
 0-1 NA 1 1 0 1
 (4-5) Overall triggers indicate a
 developing drought.

 Developing Drought - 1

 Overall triggers indicate a
 developing drought but if
 Eastern
 0 NA 2 2 0 recharge remains low and 1
 (6-8)
 demand high, this drought
 region could move to
 moderate drought in the
 fairly near future.

 Key: (0) normal drought status, (1) developing drought status, (2) moderate drought
 status, (3) severe drought status.

Figure 1.1 – Trigger schematic tool – Eastern (W) 2003

 H

 3 2 to 1
 Demand

 Aug

 Sep

 Apr
 Oct Jan
 Nov Dec
 L
 L
 2 1 to 0H
 Resources / Recharge

 0 1 2 3
 Normal Level 1 Level 2 Level 3
 Status

 PAGE 8

Drought Plan
 March 2021

To present the full 2003 scenario a timeline table (see Table 1.3) has been developed
to show when each drought region would change drought status and set out some of
the key actions that would be implemented as per the Drought Action Plan. The main
points are:

 The Drought Management team would have been convened in February / March
 2003 for all drought regions and developing drought actions commenced;
 Eastern (1-3) drought region would have been the only drought region to step up
 to a moderate drought status during July–October;
 In Eastern (1-3) drought region a temporary use ban Phase 1 would have been put
 in place in August (at the latest) to curb the high demands. It is likely they would
 have been considered in June and July and may have been implemented then,
 depending on whether adjacent water companies were implementing restrictions.
 In early September, with the reservoirs indicating a moderate / severe drought, it
 is thought likely that a temporary use ban Phase 2 would also have been
 implemented to assist with applications if drought permits/orders are required for
 winter refill;
 Drought permit/order applications would likely be submitted in October (when both
 Ardingly and Arlington indicate a severe drought status) to assist with winter refill.

The scenario has demonstrated that drought permits/orders for winter refill may be
required when overall Eastern (1-3) drought region is only at moderate drought, which
was not covered in the drought plan. During the development of the drought plan, we
made alterations to the drought permit/order triggers as a result of this.

In a comparison of this scenario to actual actions that were implemented in 2003,
there are some discrepancies. In reality, no hosepipe or sprinkler bans were
implemented during 2003. Drought permits to assist with winter reservoir water
conservation and refill were applied for The Upper and Lower Ouse, and the
Cuckmere in October / November 2003 and were granted in December 2003. The
scenario suggests that the updated triggers lead to some actions commencing
slightly earlier than might have occurred previously under the former South East
Water or Mid Kent Water.

 PAGE 9

Drought Plan
 March 2021

Table 1.3 – 2003 Drought scenario regional drought scores and summary of
actions likely to be implemented
 East West East
 Scenario (selected) actions likely to be implemented
 (1-3) (4-5) (6-8)
Jan 2003 0-1
 Drought Management Team convened
Feb 2003 East (1-3) and East (6-8) commence developing drought
 actions
Mar 2003 West (4-5) commence developing drought actions
 Arlington Reservoir at severe drought status (there are no
Apr 2003
 drought permits linked to this reservoir for summer use)
May 2003
Jun 2003 1-2
 East (1-3) moderate actions commence, including phase
 1 temporary bans likely to be advertised in very early
Jul 2003 1-2 August and implemented in mid-August when demand is
 highest (they would have been considered in June and
 July and may have been implemented immediately
Aug 2003 1-2 depending on whether adjacent water companies were
 implementing them)
 East (1-3): consider putting phase 2 temporary use bans
 in place. This is likely to have been imposed in order to
Sep 2003
 apply for winter refill drought permits. Arlington reservoir
 at severe drought status.
 East (1-3) Arlington and Ardingly Reservoirs at severe
Oct 2003 drought status. Lower Ouse and Cuckmere winter refill
 drought permits/orders applied for.
Nov 2003
Dec 2003
Key
 Normal drought status
 Developing drought status
 Moderate drought status
 0-1 Normal / developing drought status boundary
 1-2 Developing / Moderate drought status boundary

When considering the potential impacts on drought status of our override trigger
having been activated during this drought, we can conclude that in this scenario, it
would have had limited impact until June 2003 when we reached the 1-2 status
boundary. This is because prior to that point, the status of our triggers was such that
even with the potential loss of a bulk supply, we would likely be able to accommodate
that with output from our own sources. However, as our triggers approach the 1-2
status boundary, we would likely use the override trigger to move our drought status
from level 1 (developing drought) to level 2 (moderate drought). This would escalate
our action plan to take account of a neighbouring water company’s bulk supply
reduction earlier. In this way, we see the true benefit of the override trigger and how
it would have worked really well in practice.

1.1.2 Medium duration, multi season drought (1995-1997)
1995 to 1997 was selected because of the sequential years of hot dry weather with
below average recharge. The 1995-1997 scenario is considered to have a greater than
one per cent probability of occurrence in any given year, i.e. a return period of greater

 PAGE 10

Drought Plan
 March 2021

than one in 100 years. As per the 2003 drought scenario, trigger scores were collated
and entered into the drought assessment matrices for each month. An example for
August 1996 is shown below (Table 1.4, Table 1.5, and Figure 1.2), which indicates
Eastern (1-3) and Eastern (6-8) drought regions are both at moderate drought and
Western (4-5) is at developing drought status.

Table 1.4 – Initial trigger matrix for August 1996 scenario
 Groundwater Surface Water Recharge Demand
 Elphicks Farm Trial
 0 Ardingly 2 Goudhurst (Ashdown Beds) (32%) 0
East (1-3)

 (Ashdown Beds) (32%)
 Cornish (Chalk S Downs) Poverty Bottom (Chalk South
 (44%)
 2
 Downs) (44%)
 0 East (1-3) 2
 Ryarsh (Gs W of Medway)
 Arlington 2 Cramptons (Greensand West of
 (20%)
 1 Medway) (20%)
 1
 Hambledon Old Schl (Gs
 1 Cleve (Chalk Maidenhead) (25%) 0
West (4-6)

 Wy+Lod) (37%)
 Stonor Park (Maidenhead Basingstoke (East Hants Downs)
 Chalk) (25%)
 1 n/a (38%)
 0 West (4-6) 2
 Winslade Farm (E Hants Borden (Wey Loddon Greensand
 Downs) (38%)
 1 and HB) (37%)
 1
 Charing No 7 (Gs E of
 Medway) (23%)
 0 Goudhurst (Ashdown Beds) (5%) 0
 Dane Court (Chalk Stour) Cramptons (Greensand West of
 (43%)
 2 Medway) (7%)
 1
 Duckpit Farm (Chalk N Boughton (Chalk North Downs)
 2 n/a 1 East (7-8) 3
East (7-8)

 Downs) (22%) (22%)
 Elphicks (Ashdown Beds) Charing (Greensand East of
 (5%)
 0 Medway) (23%)
 1
 Ryarsh (Gs W of Medway)
 (7%)
 1 Boughton (Chalk Stour) (43%) 1
 Key: (0) normal drought status, (1) developing drought status, (2) moderate drought
 status, (3) severe drought status.

Table 1.5 – Overall trigger matrix for August 1996 scenario
 Company Trigger 1 Trigger 2 Trigger 3 Trigger 4 Override Comment Overall
 Drought Trigger drought
 Region region score
 Resources Status Recharge Demand/ Bulk
 Forecast supplies
 GW Reservoirs demand / Shared
 sources

 Moderate
 Drought - 2

 Reservoir levels
 indicate a
 moderate
 Eastern
 1 2 0 2 0 drought and 2
 (1-3)
 groundwater
 levels falling.
 Recharge
 forecasts are ok
 but demand is
 high.

 Western Developing
 1 NA 0 2 0 1
 (4-5) Drought - 1

 PAGE 11

Drought Plan
 March 2021

 Company Trigger 1 Trigger 2 Trigger 3 Trigger 4 Override Comment Overall
 Drought Trigger drought
 Region region score
 Resources Status Recharge Demand/ Bulk
 Forecast supplies
 GW Reservoirs demand / Shared
 sources

 Current GW
 indicates a
 developing
 drought and
 demand is high.

 Moderate
 Drought - 2

 Overall triggers
 indicate a
 Eastern developing
 1-2 NA 1 3 0 2
 (6-8) progressing to
 moderate
 drought.
 Demand is
 exceptionally
 high.

 Key: (0) normal drought status, (1) developing drought status, (2) moderate drought
 status, (3) severe drought status.

Figure 1.2 – Trigger schematic tool – all drought regions August 1996

 H

 3 E (6-8) 2 to 1
 Demand

 E (1-3)
 W (4-
 6)

 L
 L 2 1 to 0H
 Resources / Recharge

 0 1 2 3
 Normal Developing Moderate Severe
 Status Drought

 PAGE 12

Drought Plan
 March 2021

A timeline table (see Table 1.6) has been developed to show when each drought region
would change drought status and set out some of the key actions that would be
implemented as per the drought action plan. A comparison with what happened in
reality is also made, however it should be noted that some of the discrepancies may
be because the scenario is based on a 2003 demand profile. The main points are:

 Eastern (1-3) drought region would have been the first drought region to go into a
 developing drought status in May 1995
 As the drought continues in August 1995 Eastern (6-8) would have reached
 developing drought status, and Eastern (1-3) would have stepped up to moderate
 drought status. Western (4-5) drought region would have remained at normal status
 A temporary use ban on water use (Phase1) would have been implemented in
 August 1995 which is consistent with what happened in reality
 By October 1995 all three drought regions would have been at developing drought
 status and would stay at or above this status until late December 1997
 In late August the Company would have been considering applying for the Upper /
 Lower Ouse drought permit/order to assist with Ardingly Reservoir water
 conservation and refill (because Ardingly crossed the severe drought trigger in
 August). In reality the drought permit/order (if granted) would probably not have
 been used until December 1995. We would have applied again in December if the
 drought permit/order had not previously been granted earlier in autumn. This is
 consistent with the actual winter 1996 drought permit used
 A temporary use ban (Phase1) is likely to have been kept in place over the winter
 period but would be lifted in February because of rising reservoir levels and in case
 of need later in the summer. (A re-application of a restriction is likely to have greater
 demand savings and allow fresh communications messages)
 The July 1996 temporary use bans (Phase1) in both Eastern (6-8) and Eastern (1-
 3) are also consistent with what actually happened. Because of the extended
 duration of the drought it is likely they would have been maintained over winter
 1996-97 so that the drought message communicated remains constant
 In July 1996 the Ardingly Reservoir severe drought trigger was crossed so we
 would have been preparing and considering a Summer Lower Ouse drought
 permit/order application in mid-late July. It is however unlikely to have been applied
 for because the Eastern (1-3) drought region status was only moderate. (During
 summer a severe drought status is the trigger for drought permit/order application)
 The timing of crossing the Ardingly Reservoir severe trigger has an impact on the
 drought permit/order type applied for and when an application would be submitted.
 For example in summer 1995 the Ardingly severe drought trigger was not crossed
 until August. This would have prompted Autumn Ouse drought permit/order
 application to help refill Ardingly Reservoir, even though the drought region status
 was only moderate. This is because the drought permit/order application process
 takes about 6 weeks and if a summer Lower Ouse drought permit/order were
 applied for in mid-August, by October it would be attained too late to be of use
 In September 1996 an application for the Upper / Lower Ouse drought permit/order
 to assist with Ardingly Reservoir water conservation and refill would have been
 considered, and is likely to have been submitted, because the reservoir crossed
 the severe drought trigger
 In February 1997 Eastern (6-8) would have moved to moderate drought status. In
 reality the former Mid Kent Water drought team had only just been convened. It
 appears these triggers are prompting initial drought actions sooner than the former
 Mid Kent Water drought plan would have done. Phase 2 temporary use bans are

 PAGE 13

Drought Plan
 March 2021

 likely to be implemented in Eastern (1-3) to reduce demand and a Phase 3 drought
 order also applied for. Restrictions were not put in place in reality, although they
 were considered at the time
 In October 1997 Western (4-5) drought region reaches moderate drought but
 temporary use bans (Phase 1) would not be implemented this late in the year
 Post drought actions, including the lifting of the Phase 1 and 2 temporary use ban
 restrictions would commence in early 1998

Table 1.6 – 1995–97 Drought scenario regional drought scores and summary of
actions likely to be implemented
 East West East Scenario (selected) actions likely
 1995-1997 Actions
 (1-3) (4-5) (6-8) to be implemented
Jan 1995 0-1
Feb 1995 0-1
Mar 1995
Apr 1995
 Drought management team
 convened
May 1995
 East (1-3) developing actions
 commence
Jun 1995
 East (1-3) Ardingly reservoir trigger
 at moderate drought approaching
 severe. Permutations of the Ouse
 drought permit/order would be
 prepared (these would not have
Jul 1995 1-2 been submitted until the region was
 at severe drought status and/or the
 severe Ardingly reservoir trigger
 has been crossed in late summer
 when an autumn refill could be East (1-3) and West (4-5)
 applied for) sprinkler ban.
 East (1-3) moderate actions East (1-3) hosepipe ban)
 commence, including phase 1
Aug 1995 temporary use bans advertised in
 late July/early August and
 implemented by mid-August.
 Ardingly reservoir severe drought
 trigger crossed in August, Upper /
Sep 1995
 Lower Ouse drought permit/order
 applications in enable abstraction
 and autumn refill submitted in late
 August.
Oct 1995 East (6-8) and West (4-5)
 developing drought actions
 commence.
Nov 1995
 East (1-3) Ardingly reservoir trigger
 moderate drought, approaching
 severe drought. Assumed that
 drought permits/orders for the River
Dec 1995
 Ouse are in place. If not, we would
 reapply in December as Ardingly is
 approaching severe drought
 trigger.
Jan 1996 0-1 East (1-3) winter reservoir
 East (1-3) drought permit to
 conservation and refill drought
 allow additional abstraction
Feb 1996 permit/order assumed to be in use.
 from the River Ouse
 Likely to have revoked the phase 1

 PAGE 14

Drought Plan
 March 2021

 East West East Scenario (selected) actions likely
 1995-1997 Actions
 (1-3) (4-5) (6-8) to be implemented
 temporary ban restrictions in case East (6-8) DMT established
 of need later in summer. in early 1996
Mar 1996
Apr 1996
May 1996
 East (1-3) Ardingly reservoir trigger
 at moderate drought, approaching
 serve drought. Permutations of the
Jun 1996 1-2 1-2 Ouse drought permits/orders would
 be prepared (these would not be
 submitted until the severe drought
 trigger is reached.

 East (1-3) and East (6-8) temporary
 bans on water use phase 1 likely to
Jul 1996 be implemented in July (even
 though East (6-8) has not yet
 reached moderate drought status)
 Ardingly reservoir severe drought
 trigger crossed in mid-July, but
 because the drought region status
 is only moderate, a summer Lower
 drought permit/order application is
Aug 1996 unlikely to have been submitted.
 Permutations of the Ouse autumn
 refill drought permit/order would be
 prepared (these would not have
 been submitted until the Ardingly
 severe drought trigger reached in
 September, if considered required
 at all. Under this scenario it is quite
 East (1-3) sprinkler ban and
Sep 1996 likely that we would have decided
 hosepipe ban
 that a drought permit/order would
 not have been necessary).

Oct 1996 1-2 1-2 East (1-3) and East (6-8) phase 1
Nov 1996 restrictions kept in place over
Dec 1996 1-2 winter and into 1997 – likely to
 have been kept in place over
Jan 1997 1-2
 summer 1997 in both regions
Feb 1997 East (6-8) moderate drought East (6-8) DMT concluded
 actions commence (for example: developing drought with
Mar 1997 increase in transfer from East (1-3) possibility of moving into
Apr 1997 to East (6-8), prepare Halling No.8 moderate drought. Water
 drought permit/order in case use restrictions considered
May 1997 required (unlikely that it would have but not put in place.
 been submitted), consider phase 2
Jun 1997 1-2 1-2 temporary bans on water use,
Jul 1997 1-2 restrictions may have been put in
 place in mid-summer. If so, a
Aug 1997 phase 3 drought order would also
 have been applied for)
Sep 1997 West (4-5) moderate drought
Oct 1997 actions (phase 1 restrictions
 unlikely to be put on during
Nov 1997 0-1 Autumn)
 East (6-8) and East (1-3) temporary
Dec 1997
 ban phase 1 and phase 2

 PAGE 15

Drought Plan
 March 2021

 East West East Scenario (selected) actions likely
 1995-1997 Actions
 (1-3) (4-5) (6-8) to be implemented
 restrictions lifted. Commence post
Jan 1998 0-1 drought actions.
Key
 Normal drought status
 Developing drought status
 Moderate drought status
 0-1 Normal / developing drought status boundary
 1-2 Developing / Moderate drought status boundary

Activation of our override trigger would have had limited impact on our drought status
until we came close to reaching our level 1-2 status boundary. Therefore, if another
company hit its triggers, then it would escalate our actions to take account of a
reduction in a neighbouring water company’s bulk supply earlier than would
otherwise have been the case. In this way, we see the true benefit of the override
trigger and how it would have worked really well in practice.

1.1.3 Long term drought (2003-2006)
2003 to 2006 was selected because of sequential years of below average recharge
and high forecast demands, which for the South East of England it was recorded as a
one in 40-80 year event1, i.e. with a 1.25-2.5 per cent probability of occurrence in any
given year. The Centre for Ecology and Hydrology stated that the ‘combined
November-February rainfall deficiencies are the lowest for successive winters since
1932-1934 in much of central and south eastern England’ (Mid Kent Water, March
2006).

As per the 2003 and 1995-97 scenarios, trigger scores were collated and entered
into the drought assessment matrices for each month. An example for December
2004 is shown below (Table 1.7, Table 1.8, and Figure 1.3), which indicates the first
time in the scenario when all regions are at Moderate drought, with Eastern (1-3)
experiencing the worst drought conditions during that month.

Table 1.7 – Initial trigger matrix for December 2004 scenario
 Groundwater Surface Water Recharge Demand
 Elphicks Farm Trial
 1 Ardingly 2 Goudhurst (Ashdown Beds) (32%) 1
 East (1-3)

 (Ashdown Beds) (32%)
 Cornish (Chalk S Downs) Poverty Bottom (Chalk South
 (44%)
 2
 Downs) (44%)
 1 East (1-3) 1
 Ryarsh (Gs W of Medway)
 Arlington 2 Cramptons (Greensand West of
 (20%)
 2 Medway) (20%)
 2

1
 Return period estimates for 2003 -2006 are based on non-essential use submissions by Southern Water Services
made in spring 2006. References: Southern Water Services, March 2006 a, and Southern Water Services March
2006b.

 PAGE 16

Drought Plan
 March 2021

 Hambledon Old Schl (Gs
 1 Cleve (Chalk Maidenhead) (25%) 2
West (4-6)

 Wy+Lod) (37%)
 Stonor Park (Maidenhead Basingstoke (East Hants Downs)
 Chalk) (25%)
 1 n/a (38%)
 2 West (4-6) 2
 Winslade Farm (E Hants Borden (Wey Loddon Greensand
 Downs) (38%)
 1 and HB) (37%)
 1
 Charing No 7 (Gs E of
 Medway) (23%)
 1 Goudhurst (Ashdown Beds) (5%) 1
 Dane Court (Chalk Stour) Cramptons (Greensand West of
 (43%)
 0 Medway) (7%)
 2
 Duckpit Farm (Chalk N Boughton (Chalk North Downs)
 1 n/a 2 East (7-8) 2
East (7-8)

 Downs) (22%) (22%)
 Elphicks (Ashdown Beds) Charing (Greensand East of
 (5%)
 0 Medway) (23%)
 2
 Ryarsh (Gs W of Medway)
 (7%)
 2 Boughton (Chalk Stour) (43%) 2
 Key: (0) normal drought status, (1) developing drought status, (2) moderate drought
 status, (3) severe drought status.

 PAGE 17

Drought Plan
 March 2021

Table 1.8 – Overall trigger matrix for December 2004 scenario
 Company Trigger 1 Trigger 2 Trigger 3 Trigger 4 Override Comment Overall
 Drought Trigger drought
 Region region
 Resources Status Recharge Demand/ Bulk score
 Forecast supplies
 GW Reservoirs demand / Shared
 sources

 Moderate Drought - 2

 Eastern Reservoir levels and
 2 2 1-2 1 0 2
 (1-3) groundwater indicates a
 Moderate drought, and
 recharge forecasts are low.

 Moderate Drought - 1-2

 Current GW indicates a
 Western
 1 NA 2 2 0 Developing drought (but 1-2
 (4-5)
 increasing in severity), but
 recharge forecasts are low
 and demand is high.

 Moderate Drought - 1-2

 Current GW indicates a
 Eastern
 1 NA 2 2 0 Developing drought (but 1-2
 (6-8)
 increasing in severity), but
 recharge forecasts are low
 and demand is high.

 Key: (0) normal drought status, (1) developing drought status, (2) moderate drought
 status, (3) Severe drought status.

Figure 1.3 – Trigger schematic tool – all drought regions December 2004

 H

 3 2 to 1
 Demand

 E (E)
 W
 E (W)

 L
 L
 2 1 to 0H
 Resources / Recharge

 0 1 2 3
 Normal Developing Moderate Severe
 Status Drought

 PAGE 18

Drought Plan
 March 2021

A timeline table (see Table 1.9) has been developed to show when each drought region
would change drought status and set out some of the key actions that would be
implemented as per the drought action plan. A comparison with what happened in
reality is also made, however it should be noted that some of the discrepancies may
be because the scenario is based wholly on a 2003 demand profile. The drought year
2003 has already been discussed in Section 1.1.1 and so details for that year are not
mentioned in the discussion below. The main points for the 2004-2006 period are:

 Over the 2004 winter all drought regions would have been at developing drought
 status. Drought permits/orders for Ardingly (Lower Ouse) and Arlington
 (Cuckmere) would have been in place to assist with refill of the reservoirs and
 temporary and a Phase 1 temporary use ban would have remained in place for
 Eastern (1-3) drought region.
 During this we would have also been discussing whether there were any schemes
 that could be accelerated to assist with the drought should it continue over the next
 12 months or longer.
 In early spring 2004 we would have considered whether to lift the temporary use
 ban Phase 1 restrictions for Eastern (1-3) drought region because the drought is of
 a similar severity across the company area and the other drought regions have not
 reached the trigger for it to be implemented.
 The temporary use ban Phase 1 restrictions would have been advertised in
 September 2005, and subsequently implemented in early October 2004. This is
 probably the latest time of year we would consider putting these restrictions on,
 under this situation. This is generally consistent with the sprinkler and hosepipe
 ban that was actually implemented in summer 2004.
 In December 2004 all drought regions were at a moderate drought status. Winter
 refill drought permits/orders would not have been applied for because the
 Reservoir curves had not reached the severe drought trigger.
 In late March 2005 the Eastern (6-8) drought region would have advertised and
 then implemented the temporary use ban Phase 1 restrictions. The Western (4-5)
 drought region would have been the last implement a temporary use ban. This
 would have been advertised in early August, to be closely followed by a whole
 company Phase 2 restriction in late August. During August a Phase 4 drought
 order application would have been prepared and applied for at the same time that
 the Phase 2 restriction was put in place. Phase 3 would have been omitted
 because of the speed of the worsening severity of the drought.
 Drought permit/order applications to assist with Ardingly and Arlington winter refill
 would have been considered in October because even though both reservoirs
 indicate only a moderate drought status and overall Eastern (1-3) drought status is
 moderate; the reservoir levels were not looking like they would quickly recover. If
 granted they may not have been used until December or January. If a decision
 was taken not to apply for them, then they would have been applied for in January
 2006 when Arlington reached severe drought status and reservoir storage was
 close to crossing the drought trigger.
 All drought regions remained at moderate drought status until at least December
 2005 and the drought actions would have continued until normal status was
 resumed.

 PAGE 19

Drought Plan
 March 2021

Table 1.9 – 2003–2006 Drought scenario regional drought scores and summary
of actions likely to be implemented
 East West East Scenario (selected) actions likely to 2003-2006 summary of
 (1-3) (4-5) (6-8) be implemented key actions
Jan 2003 0-1
 Drought management team convened.
Feb 2003 East (1-3) & East (6-8) commence
 developing drought actions.
 West (4-6) commence developing
Mar 2003
 drought actions.
 Arlington reservoir at severe drought
 status. (There are no drought
April 2003
 permits/orders linked to this reservoir
 for summer use).
May 2003
Jun 2003 1-2
Jul 2003 1-2 East (1-3) moderate actions
 commence, including: Phase 1
 temporary bans likely to be advertised
 in very early August and implemented
 in mid-August, when demand is
Aug 2003 1-2 highest. (They would have been
 considered in June and July and may
 have been implemented then,
 depending on whether adjacent water
 companies were implementing them).
 East (1-3) consider putting on Phase 2
 temporary bans – likely to have been
Sep 2003 imposed in order to apply for winter
 refill drought permits/orders. Arlington
 reservoir at severe drought.
 East (1-3) Arlington and Ardingly East (1-2) winter reservoir
 reservoirs at severe drought. Apply for conservation and refill
Oct 2003
 Lower Ouse and Cuckmere winter refill drought permits (Lower
 drought permits/orders. and Upper Ouse and
Nov 2003 Cuckmere) applied for.
 East (1-3) Drought permits
Dec 2003
 granted.
 East (1-3) Phase 2 temporary bans
 lifted because surface water resource
Jan 2004
 status is improving. Phase 1
 temporary bans kept in place.
 All Regions: consider accelerating
 infrastructural connectivity or source
Feb 2004
 improvement schemes that could be
 brought online in the next 6 months.
Mar 2004 East (1-3) consider lifting Phase 1
April 2004 temporary bans this spring because
May 2004 East (1-3) is at same drought status
Jun 2004 then rest of company.
Jul 2004
Aug 2004
 East (1-3) moderate actions East (1-3) sprinkler ban
 commence, including: Phase 1 East (1-3) hosepipe ban
Sep 2004 temporary bans advertised mid-
 September and put in place early
 October.
Oct 2004
Nov 2004

 PAGE 20

Drought Plan
 March 2021

 East West East Scenario (selected) actions likely to 2003-2006 summary of
 (1-3) (4-5) (6-8) be implemented key actions
 East (6-8) & West (4-5) moderate
 actions commence, including:
Dec 2004 1-2 1-2 reviewing operational use and delivery
 programme (S1b) and operational
 works (D2b).
Jan 2005
 East (6-8) drought
Feb 2005 1-2 management team
 convened.
 East (6-8) Phase 1 temporary bans
Mar 2005 1-2 advertised in late March and
 implemented in early April.
April 2005
May 2005
Jun 2005 East (6-8) Sprinkler ban.

 West (4-5) Phase 1 temporary bans
Jul 2005 1-2 advertised in early August and
 implemented by late August. East (1-3) sprinkler ban.
 All regions – Phase 2 temporary ban East (1-3) and East (6-8)
 advertised late August and hosepipe ban.
 implemented early September. East (1-3) River Ouse
Aug 2005 - Phase 4 drought order applied for in drought permit applied for
 late August. July 2005.
 - Prepare summer and winter drought West (4-5) considered a
 permits/orders for use in all three drought permit for
 drought regions (Lower River Ouse, Greatham in 2005.
Sep 2005 Cuckmere, Southland and Oaklands,
 Halling No.8).

 Would have considered applying for
 Upper Ouse and Cuckmere drought
 permits/orders to enable reservoir refill
Oct 2005 1-2
 this autumn even though severe
 reservoir drought triggers were not
 crossed.
Nov 2005 1-2 1-2
Dec 2005 1-2
 East (1-3) Arlington reservoir at severe
 drought. Apply for Cuckmere winter
 reservoir conservation and refill
 drought permits/orders if not already
 done so this autumn. (Also likely to
Jan 2006 1-2
 have submitted a Lower Ouse drought
 permits/orders application to refill
 Ardingly Reservoir). All regions –
 continue with drought actions until
 normal status is resumed.
Key
 Normal drought status
 Developing drought status
 Moderate drought status
 0-1 Normal / developing drought status boundary
 1-2 Developing / moderate drought status boundary

 Note – Mid Kent Water i.e. the former East (6-8) drought region applied for a Drought Order to ban the
 non-essential use of water in March 2006.

 PAGE 21

Drought Plan
 March 2021

Application of our override trigger during the 2003-06 drought would mean we would
have reached moderate drought status in drought region East (1-3) a few months
earlier in 2003 and retained moderate status all the way through to January 2006. We
would have been preparing to take action a little earlier in West (4-5) and East (6-8),
but not significantly different to action being taken in any case on a prudent basis. In
this way, if another company hit its triggers then it would escalate our action to plan
with a neighbouring water companies bulk supply impacts earlier. Therefore, we see
the true benefit of the override trigger and how it would have worked really well in
practice.

1.1.4 Two dry winter drought (2010-2012)
The 2010-2012 drought is considered to be the worst experienced in the South East
Water company area in the historic record back to 1920, with a return period of
approximately 1 in 100 years (or a 1 per cent probability of occurrence in any one year).
As per the 2003, 1995-1997 and 2003-2006 scenarios, trigger scores were collated
and entered into the drought assessment matrices for each month. An example for
June 2012 is shown below (Table 1.10), which indicates when overall company
drought status is severe, following the second dry winter. Eastern (1-3) experienced
the worst drought conditions during that month.

As has been mentioned previously, the 2010-2012 drought has been illustrated using
modelled operation of our two reservoirs (Ardingly and Arlington, as presented in and
Figure 1.6) in response to observed rainfall-runoff sequences during that drought
event, as opposed to observed storage level data. This is because our two reservoirs
were operated abnormally during this period and hence using observed storage levels
would be misleading and inappropriate. The trigger matrix has been adapted
accordingly, with results from the reservoir modelling rather than operational data.

Table 1.10 – Initial trigger matrix for June 2012
 Groundwater Surface Water Recharge (2-year cumulative recharge) Demand
 Elphicks Farm Trial
 3 Ardingly 0 Goudhurst (Ashdown Beds) (32%) 3
East (1-3)

 (Ashdown Beds) (32%)
 Cornish (Chalk S Downs) Poverty Bottom (Chalk South
 (44%)
 2 Downs) (44%)
 3 East (1-3) 0
 Ryarsh (Gs W of Medway)
 Arlington 0 Cramptons (Greensand West of
 (20%)
 2 Medway) (20%)
 3
 Hambledon Old Schl (Gs
 1 Cleve (Chalk Maidenhead) (25%) 3
West (4-6)

 Wy+Lod) (37%)
 Stonor Park (Maidenhead Basingstoke (East Hants Downs)
 Chalk) (25%)
 2 n/a (38%)
 1-2 West (4-6) 0
 Winslade Farm (E Hants Borden (Wey Loddon Greensand
 Downs) (38%)
 1 and HB) (37%)
 3
 Charing No 7 (Gs E of
 Medway) (23%)
 2 Goudhurst (Ashdown Beds) (5%) 3
 Dane Court (Chalk Stour) Cramptons (Greensand West of
 (43%)
 2 Medway) (7%)
 3
 Duckpit Farm (Chalk N Boughton (Chalk North Downs)
 2 n/a 3 East (7-8) 0
East (7-8)

 Downs) (22%) (22%)
 Elphicks (Ashdown Beds) Charing (Greensand East of
 (5%)
 3 Medway) (23%)
 3
 Ryarsh (Gs W of Medway)
 (7%)
 2 Boughton (Chalk Stour) (43%) 3

 PAGE 22

Drought Plan
 March 2021

Key: (0) normal drought status, (1) developing drought status, (2) moderate
drought status, (3) severe drought status.
Table 1.11 – Overall trigger matrix for June 2012
 Company Trigger 1 Trigger 2 Trigger 3a Trigger 3b Trigger 4 Comment Overall
 Region Drought
 Resources Status Three Year Two Year Demand/ Region
 Cumulative Cumulative Forecast score
 GW Reservoirs Recharge Recharge demand

 2 Moderate Drought
 (although
 Eastern Elphicks (Both reservoirs are currently
 0 1 3 0 2
 (W) is full, Elphicks (Ashdown)
 critically groundwater levels severely
 severe) low (32% of GW))

 Developing to Moderate
 Drought

 (Groundwater levels have
 increased to developing
 Western 1-2 2 3 0 drought status in the East 1-2
 Hants Downs and Wey
 Loddon Greensand.
 Groundwater levels are still
 low at Stoner, however these
 are increasing)

 Moderate Drought
 2
 (although
 (Chalk groundwater levels
 Eastern Elphicks
 1 3 0 have increased to moderate 2
 (E) is
 drought status. Elphicks
 critically
 (Ashdown) groundwater levels
 severe)
 severely low (5% of GW))

 Key: (0) normal drought status, (1) developing drought status, (2) moderate drought
 status, (3) severe drought status.

Figure 1.4 – Trigger schematic tool showing 11 June 2012 to 30 June 2012

 H

 3 2 to 1
 E (W)
 Demand

 E (E)

 W

 L
 2
 L
 1 to 0H
 Resources / Recharge

 PAGE 23

Drought Plan
 March 2021

 0 1 2 3
 Normal Mild Moderate Severe
 Status Drought Drought Drought

Figure 1.5 – Storage at Ardingly Reservoir during the 2010-2012 drought event

 PAGE 24

Drought Plan
 March 2021

Figure 1.6 – Storage at Arlington Reservoir during the 2010-2012 drought event

It can be seen from Figure 1.5 and Figure 1.6 that reservoir levels during the 2010-
2012 drought were in fact not badly affected by the low rainfall. This is due to the
fact that the drought was characterised by a prolonged period of low rainfall covering
two dry winters, which has a more significant impact on groundwater levels than
reservoir storage (volume and recovery/refill), which can be refilled quickly even at
such low rainfall levels, e.g. during its refill season, Arlington only requires three
months of 30 per cent of LTA rainfall to reach capacity. As such, our reservoirs are
more vulnerable to short, sharp drought events which result in high demands being
placed on the system, such as the 2003 drought event described earlier in section
1.1.1.

Our actions during this type of drought event are set out in Table 1.12. The summary
of key actions in this table show only the new drought actions that were initiated each
month: when a new drought management action is initiated, the preceding actions
are continued unless otherwise stated, but are not repeated in each row of the table
for presentational reasons. These actions are aligned with those we would initiate
based on section Error! Reference source not found. of this drought plan. The
egional drought scores shown in Table 1.12 demonstrate that although groundwater
levels were impacted by the two dry winter drought, the overall picture across the
regional triggers, showed only the East (1-3) region reaching severe drought (level 3)
during the latter stages of the event, in late winter/early spring 2012. Illustration of
our actions and the progression and recession through our drought trigger levels
shows that across most of our area we were able to balance supply and demand

 PAGE 25

Drought Plan
 March 2021

without recourse to all of our surface water drought permits/orders, or to a drought
order to restrict the non-essential use of water. The drought broke in summer 2012.
However, this drought highlighted to us that a third dry winter could have the potential
to move all our regions into the level 3 ‘severe’ drought trigger zone, requiring
preparation for additional drought permits/orders. This initiated consideration of a
third dry winter drought scenario, which has been described in section 1.2 below.

Table 1.12 – 2010-2012 Drought scenario regional drought scores and
summary of actions implemented
 East West East
 2010-2012 summary of key actions
 (1-3) (4-5) (6-8)
Oct 2010 1 1 0
Nov 2010 1 1 0
 Based on the current drought status, watching brief is maintained
Dec 2010 1 2 0
 on a monthly basis.
Jan 2011 0 1 1
Feb 2011 0 1 1
 Developing drought conditions observed, although the
Mar 2011 1 1 1
 Company’s resources position remains good.
 Developing drought status closely monitored given the low
Apr 2011 1 1 1 rainfall and higher demands. Consideration given to media
 messages to customers during May reminding everyone to use
 water wisely during the good weather.
 Media messages deployed reminding everyone to use water
 wisely during the good weather. South East Water started to
 assess the impacts for next summer, under a scenario of a dry
May 2011 1 1 1
 summer this year followed by a dry winter with low recharge, this
 includes reviewing current site output capacities and potential
 capital schemes/other measures.
June 2011 1 1 1
July 2011 1 1 1
August 2011 1 1 1
September
 2 1 1
2011
 Initiation of weekly reservoir drought meeting, continuation of
 formal drought meetings, sources optimised to increase output,
October 2011 2 1 1 additional sources being investigated including reinstatement of
 disused sources, enhanced leakage detection programme being
 implemented, high demand commercial users being investigated
 and water efficiency audits being taken
 Communication plans on-going.

November Drought order submitted to the Environment Agency and Defra to
 2-3 2 2 reduce the Lower Ouse MRF and conserve storage; drought
2011
 permit for Arlington Reservoir considered, to be submitted to the
 Environment Agency during December.

December Summer drought permits/orders reviewed. Drought permit for
 2-3 2 2 Arlington Reservoir considered, but due to the high river levels
2011
 and the ability to refill the reservoir the application is put on hold.
 Planning for worst case conditions through the summer / into
January 2012 3 2 2 early next autumn. This includes potential imposition of customer
 restrictions, from as early as April 2012. Summer drought
 permits/orders reviewed.

 PAGE 26

Drought Plan
 March 2021

 East West East
 2010-2012 summary of key actions
 (1-3) (4-5) (6-8)
 Proposed customer restrictions published for representation.
February
 3 2 2-3 Additional drought permit/order for Ardingly Reservoir prepared.
2012 Work to assess impacts of a third consecutive dry winter scenario
 commenced.
March 2012 3 2 2-3
 Temporary use ban restrictions in place from 5th April 2012.

 Drought permit to lower the MRF at Barcombe prepared and the
April 2012 3 2 2-3 draft circulated to the Environment Agency and stakeholders for
 review. This drought permit has been drafted for implementation
 under worst case scenario from the 1st July. Additional drought
 permits considered, in discussion with the Environment Agency.
 The drought permit prepared no longer required given
May 2012 2-3 1-2 2-3
 improvements is storage levels at Ardingly Reservoir.
 Further restrictions and drought permits/orders now unlikely as
June 2012 2 1-2 2
 drought recovery commenced.
July 2012 2 0-1 1-2 Review of lessons learned during the recent drought
 Prudently proceeded with a number of drought management
August 2012 1-2 0-1 1-2 schemes that offer benefit next spring should there be a dry
 winter.
September
 1-2 0-1 1-2
2012
 De-escalation of drought activity: Formal drought management
 team stood down. But meetings retained in diaries should the
 need to re-enact the team be required. Enhanced leakage
 detection programme remains in place but level of enhancement
October 2012 0-1 0 1-2 continuously under review. Further pressure management work
 that commenced during drought continues to completion.
 Progress continues on a number of schemes that were originally
 being progressed to mitigate for a further dry winter. Review of
 lessons learned during the recent drought is continuing.
 Normal drought status
 Developing drought status
 Moderate drought status
 Severe drought status
 0-1 Normal / developing drought status boundary
 1-2 Developing / moderate drought status boundary
 2-3 Moderate / severe drought status boundary

1.1.5 Overall findings from the historic scenarios
As would be expected, each of the drought scenarios has a slightly different effect on
the three drought regions. They have demonstrated that the trigger and actions
methodology proposed is flexible enough to help make drought decisions in a timely
manner.

The key findings demonstrated that:

 Winter refill drought permits/orders may need to be applied for when overall the
 drought region is at a moderate drought status. The trigger that we will use for
 submitting a reservoir refill drought permit/order application is when the reservoir
 falls below the severe drought curve. The application for this type of drought
 permit/order would be submitted between August and February inclusive. The

 PAGE 27

Drought Plan
 March 2021

 preparation of this type of drought permit/order would be undertaken during the
 early/middle stages of the drought, for example when the reservoir falls below the
 moderate drought curve, in order to allow sufficient time for the necessary
 environmental assessments to be undertaken in support of the Permit application.
 Preparation of surface water drought permits/orders is estimated to take 1-2
 months. Wherever possible we would look to base permit/order applications on
 previous applications we have submitted, in order to expedite the process.
 Drought permits/orders for both reservoir refill during spring to early autumn, and
 for the drought permits/orders to increase supply, are not likely to be applied for
 until each drought region as a whole is at severe drought status (however
 applications would be prepared in advance of submission during the early and
 middle stages of the drought).
 The latest time we are likely to implement temporary use bans over the autumn to
 winter period is in October. Demands are generally higher in spring / summer so
 this type of action will have a greater effect at this time of year. In winter demand
 saving reductions from temporary use bans are considered to be negligible.
 If we are faced with a longer-term drought which fluctuates between developing –
 moderate – developing status, once temporary use ban restrictions have been
 implemented they are likely to be kept in place because we consider it important to
 maintain a consistent drought message until the drought is in recession. Constant
 lifting and re-implementation of temporary use ban restrictions would create
 confusing communications messages. However, as shown during the 2004
 drought scenario year, there may be a case for lifting restrictions during a long
 drought, to ensure consistency in communications about the severity of the
 drought. In this case only one drought region had temporary use ban restrictions
 in place for the previous summer and by the following spring all drought regions
 were at a similar drought situation. It would not be justifiable to customers to, in
 that situation, be implementing inconsistent actions.
 In each of the scenarios (with the exception of the 2010-2012 drought during which
 the temporary use ban restrictions were already in place in their current form), the
 application for the temporary use ban restrictions appeared to have been triggered
 (using this new methodology) slightly before the former hosepipe ban was applied
 for in reality. Our new Phase 1 restriction primarily restricts domestic hosepipe use
 but does offer concession to some users (e.g. disabled customers) and for several
 uses (e.g. watering food crops) and some small businesses. It is not as restrictive
 as the former hosepipe ban and so we consider that it is justifiable to bring in these
 restrictions slightly earlier.
 If the drought is increasing in severity quickly, as it did in August 2005, a Phase 3
 drought order may be omitted and the Phase 4 drought order applied for directly.

1.1.6 Historic scenario testing conclusion
We have tested the drought plan approach against the most significant low rainfall
events since the 1930s and have shown that it is sufficiently robust and is in line with
the requirements to ensure customer water needs are protected during such events.
The modelling confirms that even under the three to four-year duration droughts (that
were considered most severe during the last 20 years), the severity in terms of overall
drought region drought status is only developing – moderate. The 2010-2012 drought
did, however, take our drought region status into severe following the second dry
winter. We have taken this analysis a stage further in section 1.3 where we test our
plan against a third dry winter scenario.

 PAGE 28