EXECUTIVE SUMMARY
Introduction
The Lesotho Highlands Development Authority’s
(LHDA) Instream Flow Requirements (IFR) Policy was approved by the Lesotho
Highlands Water Commission (LHWC) on 13 December, 2003. Seven months later, on 30 July 2003, the IFR
Procedures, which provide the operational framework for implementation of the
Policy, were also agreed and approved.
IFR is a management system for dam
releases for environmental maintenance of downstream river reaches impacted by
the dams. IFR
management is still in its infancy in Southern Africa. The Lesotho Highlands
Water Project therefore provides a valuable case study in understanding the
associated management of environmental ecosystems in downstream river reaches
within the Southern African context.
This report records progress in LHDA’s efforts to fulfil the IFR Policy
requirements for the period from approval of the IFR Policy until September
2004. It also provides information on
the implementation of mitigation and compensation measures undertaken for flow
related impacts on the resources, ecosystems and communities in downstream
areas, and other secondary or indirect losses.
In addition, it addresses lessons learned and presents recommendations
for improved implementation.
Compliance against release targets
The setting of IFR bulk-water allocations for the period under reporting
was not without difficulties as a result of inexperience and significant
fluctuations in the monthly rainfall. The year was projected to be a Plus 1 hydrological year class (HYC)
for the Katse locality and an Average
hydrological year for the Mohale area.
Releases from Katse for the period Jan to September 2003 totalled 256.61 MCM, which
considerably exceeded IFR policy requirements due to various flood test
releases, and spilling from the reservoir.
Releases during the period October 2003 to September 2004 were frequently, and in aggregate,
below the target releases that were set to achieve desired flows at IFR Site
2. Flows at Site 2 itself could not be
measured as the measuring station is only about 1060 metres downstream of the
Katse dam structure and is upstream of the Khohlonts’o tributary inflow. The
Khohlonts’o stream, which is unmonitored, directly contributes to the flow at
IFR site 2, which is some 3060 metres downstream of the dam and 2000 metres
below the Katse bridge hydrometric station. It is therefore not possible to
determine with accuracy whether actual IFR site 2 flows matched the target
flows.
Releases from Mohale from the time of impoundment in October 2002 until
the end of July 2003 were subject to the Washington Agreement. For the period October 2003 to September
2004, the water volume of flow recorded at IFR site 7 was 49.31 MCM against a
target of 70.12 MCM, a 30% total deficit over the year. This was despite the fact that releases from
Mohale dam of 37.56 MCM considerably exceeded the target release of 27.36
MCM. The explanation is that inflows
from the incremental catchment between Mohale dam and IFR site 7 were
consistently less than had been assumed.
Major adjustments to the release schedules were effected because of the
prevailing conditions experienced. Incident Reports detail these changes.
Adjustments resulted in the IFR releases varying from those for a Plus 1 to a
Minus 2 hydrological year. The spring flood in August 2004 could not be
released due to the absence of suitable natural climatic conditions at the
time. Scheduled flood releases are intended to supplement naturally occurring
floods as and when they occur. Spring freshets and small floods are significant
cues for fish and invertebrate breeding cycles that cannot be ignored.
Overall, flood releases could not be effected as scheduled because of
the prevailing dry condition throughout winter, early spring and summer 2003
and because of the absence of naturally occurring flood events. It was only in
April 2004, at the onset of a high rainfall, that a flood was released.
The decision was also taken to increase releases from Mohale dam in an
effort to compensate for the accumulating deficit in target flows at IFR
site. The deficit appears to have been
the result of inflows from the incremental catchment between Mohale Dam and IFR
site 7 being less than calculated. The
manipulation of releases in the short term had the effect of evening out the
low flow releases to being nearly constant. On the other hand, releases from
Katse for the October ’03 to September ’04 period have also shown absence of
variability of flow.
Although the IFR Procedures provide for the full spectrum of climatic
conditions – as reflected by river flows – it was found that annual adjustment
of the hydrological year was inadequately responsive to changing climatic
conditions.
Resolution reached relating to flood releases
The LHDA has now accepted that the
release of certain floods under all hydrological year classes is a critical
aspect of water management. Various options for dealing with such extreme dry
events will be explored. This will include:
- Re-scheduling the flood within a particular season as the case
might be,
- Releasing it as a set of smaller freshets over a period of two
months,
- Reducing the size and duration of the flood.
Verification of river condition status
Water quality monitoring
information was not effectively evaluated to enable credible and conclusive
statements about river condition status. In addition, the biophysical
monitoring exercise was substantially delayed and could not provide useful
information. There were also significant problems in the characterization of
the environmental quality objectives being monitored; namely, the criteria laid
down in the river condition classification. The lack of precision in the
criteria meant that interpretation of conditions was dependent on extensive
experience in this very complex field, a depth of experience which the LHDA has
not yet been able to build. Specialist guidance has not been available to the
organization on an ongoing basis, but this is about to change with the imminent
appointment of a consultant to manage the implementation of the full
biophysical monitoring programme.
Related challenges include:
Ø
In-house
monitoring emphasis has focused on IFR sites 2 and 7, on a pilot basis. But,
given the critical relationship between monitoring and compensation for
resource losses, the LHDA acknowledges that all the sites have to be monitored and is putting in place a
strategy to address this.
Ø No direct comparison can be
made between baseline studies conducted in the IFR Study (Contracts 648 and
678) and the LHDA monitoring exercises.
Again, the appointment of the monitoring consultant should see this situation
improving.
Compensation and socio-economic monitoring
The implementation of IFR
procedures in determining compensation mitigation measures was undertaken
effectively. It was a participatory process where appropriate and relevant key
stakeholders were involved to discuss issues of preparation, implementation and
monitoring. To this effect, communities in IFR Reaches 1, 2 and 3 were
mobilized into twenty-three (23) formal structures (Local Legal Entities
(LLEs)) in preparation for receipt of the first 10-year tranche of the cash
compensation payment, which was disbursed to these LLEs in May, 2004. An
interim, in-house team is providing technical assistance to the LLEs who have
received communal cash compensation.
On the other hand,
preparation of affected communities in IFR Reaches 7 and 8 to receive their
compensation was not scheduled to commence until April 2005. A first round of
consultation with communities in reaches 7 and 8 was undertaken during 2003,
but the detailed preparation for the establishment of LLEs and payment remains
to be completed.
The LHDA is currently in
the process of procuring the services of a Consultant to develop and implement
the monitoring protocol for measuring and evaluating the socio-economic status
of affected communities in downstream river reaches, as required by the IFR
Policy.
Way forward
Ø Further revision of the
Procedures, under the guidance of an IFR specialist, is required. This revision
will consider the revised approach of setting IFR release targets on a quarterly
basis, as well as examining the feasibility of using the Water Balance model
projection of yields for the following year to set the IFR annual flow
schedule.
Ø Scheduled floods will not to
be cancelled but may be rescheduled as necessary to coincide with naturally
elevated river flow.
Ø Training LHDA technical
staff in the use of the DRIFT database, and linking this to the results of
biophysical monitoring, will be undertaken.
Ø LHDA will endeavour to
reduce delays in internal approval procedures.
Ø The initiation of the IFR
biophysical monitoring Contract 1237 will be fast-tracked. The focus will be on
the following aspects:
·
Revision
of the river condition classification and refinement of the measuring criteria.
·
Development
of very specific protocols and methods for monitoring against these criteria.
· Rigorous training in
monitoring purpose, field methodologies and analytical techniques.
·
Development
of a template for reporting each monitored component.
Environmental and social issues were
incorporated as legally binding articles in the founding Lesotho Highlands
Water Project (LHWP) Treaty signed by the governments of the Kingdom of Lesotho
and the Republic of South Africa for Phase I of the Project in October, 1986. In particular, Articles 7(18) and 15 of the
Treaty enjoin the Lesotho Highlands Development Authority (LHDA), the agency
established to implement the part of the Project in Lesotho with responsibility
for:
- operations and maintenance of dam and
hydropower structures
- instituting mitigation measures for the protection and preservation
of the natural and socio-economic environment.
Initially, environmental management efforts
were focused on the upstream areas of the LHWP reservoirs. However, in keeping with emerging experience
in the development of large dams worldwide, LHDA appointed consultants to
undertake an assessment of the instream flow requirements of river reaches in
Lesotho downstream of the Project dams and to predict the impacts of reduced
flows on downstream ecosystems and human communities. This was effected during
1996-2002 through LHDA Consulting Contracts No. 648 and 678. The information would establish the extent
of deterioration suffered by the downstream ecosystems and impacts on
communities as a result of modified river morphology.
The study area covered about 600km
of river reaches; namely Senqu, lower Senqunyane, lower Malibamats’o and
Matsoku rivers. This study was groundbreaking with respect to the importance
that was attached to the level of socio-economic impacts of flow modifications
in the receiving environment downstream.
In addition, realising that increasing downstream releases above the
“Treaty minima” for IFR purposes would have impacts on the project yield, hence
on project benefits, an additional study was commissioned to model the impacts
of IFR flows on project economics.
The completion of IFR studies in 2002 led to a
process of formulating an IFR Policy that would guide the management of releases
from the LHWP dams for the maintenance of downstream river health. It was approved by the Lesotho Highlands
Water Commission (LHWC) in December 2002. Further changes were effected that
resulted in the issue of a Second Edition of July 2003 Incorporating Corrigenda
of July 2003.
In developing the IFR policy and
procedures, the Project Authorities had to:
·
Attain
an optimal balance between water resources development goals and effective
maintenance of river the health
·
Assess
and evaluate the trade-offs between river condition, community needs, and the
implications of the different release options vis a vis probable
financial and economic losses for the two countries
·
Assess
and evaluate “reasonable measures” for maintaining the welfare and livelihoods
of affected persons and communities, and for ensuring the protection of the
quality of the environment in line with the Treaty stipulations.
The IFR
operational procedures took quite some time to finalize. They were only
approved in July 2003. The IFR Policy
however became effective from its approval in Dec 2002 and this report covers the period
from January 2003 to September 2004.
Releases from Mohale for the period January to July 2003 were in
accordance with the Washington Agreement for Impoundment of Mohale Dam.
The overall purpose of the IFR
Policy of the LHDA is to provide guidance for the management of flow releases for the maintenance of riverine
ecosystems downstream of Phase 1 dams. It will also provide guidance for the
mitigation measures aimed at addressing flow related impacts on resources,
ecosystems and communities downstream of the dams for both direct and indirect
or secondary losses.
1.4
Objectives of the Report
The purpose of this report is to describe
Policy implementation activities and evaluate LHDA’s performance against IFR
Policy objectives, and report these matters to stakeholders. An annual report
on the hydrological year is a commitment of the IFR Policy.
The report examines implementation
performance and compliance with the three main aspects of the IFR Policy and
Procedures, namely:
·
Target IFR releases and dam operating procedures. That is, to what extent did the actual flow
releases comply with the target set under the IFR Policy?
·
River condition targets. That is, to what extent did the flows released permit the
achievement of the downstream “river condition” targets? This is to be done by means of the IFR monitoring programme i.e.,
biophysical and socio-economic monitoring; and
·
Compensation
and mitigation procedures related to impacts on affected communities. That is:
-
To what extent were the compensation and
mitigation measures provided for under the IFR Policy implemented?
-
To what extent did the compensation and
mitigation measures achieve LHDA’s Treaty obligation to ensure that no one is
worse off as a result of the project?
1.5
The Report Structure
The report will present
·
Operations
or tasks undertaken under each of the three aspects under 1.4 above
·
Lessons
learned from the LHDA’s performance
·
Recommendations
for effective and efficient management of IFR releases.
The Policy specifies the core
components of a system to manage releases from dams in order to:
i.
Guarantee
that water will be reserved for riverine ecosystems and communities downstream
of control structures
ii.
Ensure
that the reserved water is made available to the ecosystems at the appropriate
quality, quantity and time, including responses to any emergency environmental
events;
iii.
Maintain
target river conditions in the affected river reaches, as specified in the
Policy;
iv.
Provide
information towards an appropriate IFR management amenable to a periodic review
and performance audit of the policy and its implementation.
These management procedures are described as
the Adaptive Management System. They are designed to meet the IFR policy
objectives. The IFR Adaptive Management System is based on the model known as
the Downstream Response to Imposed Flow Transformations (DRIFT) and entails
operational procedures, monitoring compensation, mitigation evaluation review
and audit as well as mechanisms for public engagement.
It is important also to note that IFR releases
are especially targeted to achieving specified river conditions states as
depicted in Tables 2-1 and 2-2.
2.1.1
River condition
classification
The Policy committed the Project to delivering
a specified percentage of the Mean Annual Runoff (MAR) or target flow at each
of the IFR sites downstream of Katse, Matsoku and Mohale dams. (Policy clause 5.1.1 and Table 5.1). The target flows at these sites are not the
same as the releases from the dams. Dam releases were calculated so that
incremental flow contributions from the catchment area between the dam wall and
applicable IFR site would result in the target flows at the IFR site.
River condition classification is described as
a condition brought about by the effect of the target flows and existing
environmental condition to meeting the desired environmental quality objectives
for the indicated river reach. Table 2-1 provides information on the extent of
the river reach and related river condition class. Table 2-2 gives a
description of river condition classes for Lesotho rivers in accordance with Tables 4.1 and 4.2 in the Policy.
Table 2‑1: Target River
Condition Classes for river reaches affected by LHWP
|
Reach
|
Description
|
Targeted
river condition class or ‘state’
|
|
Reach 1
|
Matsoku River,
from Matsoku Weir to confluence with Malibamats’o River (30 km)
|
3
|
|
Reach 2
|
Malibamats’o
River, from Katse Dam to confluence with Matsoku River (18 km)
|
4
|
|
Reach 3
|
Malibamats’o
River, from confluence with Matsoku R to confluence with Senqu R (35 km)
|
4
|
|
Reach 4
|
Senqu River
between confluences with Malibamats’o and Tsoelike rivers (115 km)
|
3
|
|
Reach 5
|
Senqu River
between confluences with Tsoelike and Senqunyane rivers (90 km)
|
2
|
|
Reach 6
|
Senqu River,
from confluence with Senqunyane River to South African border (150 km)
|
2
|
|
Reach 7
|
Senqunyane
River from Mohale Dam to confluence with Lesobeng River (90 km)
|
4
|
|
Reach 8
|
Senqunyane
River, from confluence with Lesobeng River to confluence with Senqu River (40
km).
|
3
|
|
Reach 11
|
Nqoe and Hololo
Rivers, from Muela Tailpond to confluence with the Caledon River (13 km)
|
2
|
Source: Table 4.2
of IFR Policy
Every year, in the month of October, the LHDA
sets about determining the yield targets for Katse and Mohale dams for the
following calendar year. The level for each dam is factored into the
Water-Balance model for the system and programmed to generate expected yield
for the following year. The yield schedule is approved by the Commission for
implementation at the beginning of January of each year.
The procedure for setting the annual IFR
release schedule is such that its implementation is synchronized with natural
cycles so that the ‘IFR’ year would be the hydrological year starting in spring
in the month of October. Both the natural cycles and the IFR release schedules
are subject to approval by the LHWC.
IFR release management is based on the
Downstream Response to Imposed Flow Transformations (DRIFT) hydrological Model.
The steps involved in determining the scheduled releases are outlined in Figure
2-1. The model links changes in the flow regime to environmental impacts.
The concept of classifying the next
hydrological years through a projected rainfall model to predict the next
‘hydrological year class’ (HYC) was developed. A decision was reached to have
such HYCs sub-divided into 5 such classes, namely:
·
+ 2
representing - Very Wet Year
·
+1 representing - Moderately wet year
·
0
representing - Average
·
-
1 representing - Dry year
·
- 2
representing - Severe drought.
Annex A sets out the release schedules for
Katse and Mohale for each HYC.
Table 2‑2: Definitions of the River Condition
Classes for Lesotho rivers using key indicators / descriptors
|
Indicator
|
Class/State 1
|
Class/State 2
|
Class/State 3
|
Class/State 4
|
Class/State 5
|
|
|
Pristine
|
Near natural
|
Moderately modified
|
Significantly modified
|
Severely modified
|
|
|
GEOMORPHOLOGY/HYDRAULICS
|
|
|
Instream Habitat
Diversity
|
Full
natural diversity
|
5-15% loss
in diversity
|
15-40% loss
in diversity
|
40-70% loss in diversity
|
>70% loss in diversity
|
|
|
Pool depth
|
Natural
|
5-15% loss
in depth
|
15-40% loss
in depth
|
40-70% loss in depth
|
>70% loss in depth
|
|
|
Bank erosion or
collapse
|
<5% of
bank area
|
5-10% of
bank area
|
10-20% of
bank area
|
20-40% of bank area
|
>40% of bank area
|
|
|
WATER QUALITY
|
|
|
Mean monthly
temperature1
|
Natural
|
< 3OC
|
< 4OC
|
< 5OC
|
< 6OC
|
|
|
pH annual range* change
|
Natural
|
< 0.5 pH
units
|
< 1.0 pH
units
|
< 1.5 pH units
|
< 2 pH units
|
|
|
Rapid Biological
Assessment Score
|
Total Score: Unknown
|
Total Score: ≥
95
|
Total Score: 94-70
|
Total
Score: 69-45
|
Total
Score: < 45
|
|
|
VEGETATION
|
|
|
Zone
definition2
|
All present
and distinct
|
All present
and distinct
|
Loss of
≤ 2 zones and/or zone definition less distinct
|
Loss of
≤ 3 zones and/or zone definition indistinct
|
No
definition
|
|
|
Species composition of
riparian vegetation
|
Full complement
|
Change in ratios of
indigenous species
|
Dominated by hardy
indigenous species and/or exotic species
|
Dominated by exotics
and/or weedy indigenous species
|
Dominated by one or two
species, often > 80% exotics OR no plants
|
|
|
Structure
|
Full array of growth
forms
|
5-10% reduction in
growth forms
|
11-25% reduction in
growth forms
|
26-50% reduction in
growth forms
|
> 50% reduction in
growth forms
|
|
|
FISH
|
|
|
Community composition
|
Full complement of
indigenous species in natural proportions.
No exotic species.
|
Full complement of
indigenous species, plus very low numbers of exotic species
|
Noticeable shifts in
natural community structure, moderate numbers of exotic species
|
Very few natural fish
and/or exotic fish dominate
|
Very few fish dominated
by exotic species
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1 After South African DWAF Guidelines (1999); values
given represent degrees Centigrade change from the natural mean monthly
temperature
2 Zones include: Aquatic Zone, Lower
Wetbank Zone, Upper Wetbank Zone, Lower Dynamic Zone, Tree/Shrub Zone, Back
Dynamic Zone (Report LHDA 648-F-16)
* pH Annual Range refers to the change in pH
units, not levels
Source: Table 4.1 of IFR Policy
The hydrological year, October 2003
to September 2004 was not a typical rainfall year for Lesotho. The country
experienced severe drought conditions. However rainfall in the Mohale and Katse
catchments was not as adversely affected and runoff was only slightly below
average in aggregate. It was evident,
however, that annual adjustment of the hydrological year classification was
insufficiently responsive to actual climatic variability and a modification of
the IFR Procedures is proposed.
Figure 2‑1: Procedure for determination of the IFR
releases at Katse and Mohale dams
|
|
Step 1
Classification of hydrological record for IFR sites 1, 2 and 7
|
|
Determination of adjusted bulk IFR volume allocation for each
hydrological year class
|
|
Step 2
Confirmation of Policy- stipulated IFR maintenance bulk allocation
(%MAR per site)
|
|
Implementing the
IFR Policy has met with a number of challenges, including
Ø The effective commencement
of the Policy coincided with the first dry cycle since the impoundment of Katse
Dam in October 1995. The provision in
the Procedures allowing for annual adjustment of the predicted hydrological
year classification was too slow to respond to natural fluctuations in climatic
conditions,
Ø The IFR Policy set bulk water (annual volume of flow) targets to be met
at the proximal IFR sites, which are downstream of the dams, and worked back
from these to projected water releases from the dams. In other words, there is
a difference in bulk allocation between the dam release and the IFR site, the
difference to be made up by the calculated runoff generated from the
intervening catchment.
Ø The use of Instream Flow Requirement concepts as an operating framework
for large dam releases is still in its infancy in Southern Africa. There are
numerous challenges in operationalizing the theory.
The following sections provide
information on the actual releases for IFR purposes from Phase 1 structures for
the period January 2003 to September 2004.
2.2.1
Katse Dam releases and
downstream Malibamats’o River
Katse Dam releases - January to September 2003
Katse was first described as experiencing a
Plus 1 Hydrological Year, i.e. a wetter than average year (see Table 2-4). By late
winter/spring 2003, it was apparent that climatic conditions were more towards
being characteristic of drought conditions. A spring within-year flood release,
scheduled for August, could therefore not be effected.
The discussion around implementing
the August flood was thoroughly reviewed with the decision undertaken to cancel
the flood occurrence during the month, because it would have additional stress
on the system. The cancellation was
based more on ecological consequences.
The hydraulic character of the river during drought periods was not
taken into consideration for it would have demonstrated other management
options such as:
·
releasing
the flood in a later spring month
·
reducing
the size and duration of the flood
·
splitting
the flood into small ‘freshets’ released over a two or three month period.
During incidences of drought cycles, there may
be events of high rainfall resulting in elevated river flows, which must be
taken into account in the management of the river downstream.
A constant release of water from the
compensation valve was effected at the rate of 0.75 m3/s during the
above period. This translated into a monthly low flow release of approximately
2 million cubic metres (MCM) (see Target Release column in Table 2-3) which was
in accordance with Treaty requirements of a minimum rate of flow at all times
of 0.5 m3/s but not with the IFR Policy which had been approved but
not yet implemented.
However, a number of tests were also
performed during this period:
·
Assessment
of the integrity of the compensation release valve to perform under higher flow
volumes was also undertaken.
·
A
flood of 11.24 MCM was released in April 2003 to investigate downstream thermal
impacts of flood releases.
No IFR flows were released for the remaining
period May- September 2003, because of the tests being undertaken.
The actual downstream flows at Katse
constituted 62.3% of the MAR for the period as a result of the flooding
exercise and spilling of the dam.
The IFR Policy commitment for releases from
Katse dam are 12.1% MAR.
Table 2‑3: Katse Dam
releases January 2003 to September 2003
|
Month*
|
Hydrological Year Classification
|
Katse Release Target Volume
MCM
|
Katse Release Actual
MCM
|
Hydrometric Station
Flow Volume
MCM
|
Monthly Ave Inflow (Rainfall-Runoff
Model)
MCM
|
Katse Inflow2 (Water Balance
Model)
MCM
|
|
Jan-03
|
Not
classified: IFR Procedures implemented for Katse in October 2003 due to
running of various tests of release structures
|
2.01
|
138.18
|
32.79
|
78.8
|
62.40
|
|
Feb-03
|
1.81
|
59.32
|
29.96
|
83.5
|
18.19
|
|
Mar-03
|
2.01
|
1143.36
|
70.00
|
71.7
|
126.24
|
|
Apr-03
|
1.94
|
13.39
|
13.55
|
47.1
|
21.81
|
|
May-03
|
2.01
|
2.21
|
3.62
|
22.3
|
13.99
|
|
Jun-03
|
1.94
|
2.19
|
3.48
|
12.0
|
10.52
|
|
Jul-03
|
2.01
|
2.17
|
4.06
|
10.1
|
4.98
|
|
Aug-03
|
2.01
|
2.43
|
4.03
|
13.1
|
8.80
|
|
Sep-03
|
1.94
|
2.36
|
3.83
|
21.3
|
8.09
|
|
Oct
|
Reported
in Table 2.4 for year 2003-2004
|
55.0
|
7.74
|
|
Nov
|
72.1
|
15.08
|
|
Dec
|
61.8
|
20.72
|
|
Total
|
|
17.68
|
256.61
|
165.32
|
359.9
|
275.02
|
* Data
derived from long-term hydrological model used for the IFR studies. They are
included simply to illustrate the long-term average
expected runoff in the system, as a comparison against the calculated actual
inflows. The table also shows
·
Monthly inflows to Katse dam calculated by the
system Water Balance Model, (= correlates dam water level with inflow)
·
The long-term average monthly runoff estimated
by the Rainfall-Runoff long-term hydrological model. The purpose is to demonstrate the comparison between long-term
average runoff against variations in inflow which may be experienced in a
single annual cycle. These figures also serve to illustrate reasoning behind
pronounced adjustments of IFR releases to be effected in the following
hydrological year, October 2003 - September 2004, when the IFR Policy and
Procedures would be engaged implemented fully for the first time.
The figures represent Malibamats’o catchment flows into
Katse, the transfers from Matsoku weir having been subtracted.
Katse Dam releases - October 2003 to September
2004
In September 2003, the LHDA requested that the
remaining months of the year be re-classified to Average due to the dry
conditions. It was in September that the low flow rates were increased. This
was because of the successful testing of the integrity of the
compensation valve under higher flow rates (Katse Incident Report September
2003). The low-flow rates were
increased by taking some volume from the scheduled November flood.
The approval for HY re-classification was
received much later. Releases for October, November and December 2003 were
confirmed under Plus 1 river target conditions. A subsequent request was submitted to downgrade the next three
months; January-March 2004 to Minus 1 HYC due to the prevailing dry conditions
experienced of the past three months.
The February flood was missed but was later
compensated for through a release of two small floods with a magnitude of 31m3
from 30th April to 2nd May 2004.
Figure 2-2 illustrates that the targeted flood
release for April arrived in the system late, in May. Practically only one out of a potential four scheduled
within-year floods for any of the hydrological year classes applied, was
effected, albeit, it was delayed. However, the scheduled January flood for a
Minus 1 year was not released and the low flow released characterises to a
Minus 2 HYC. At the same time, the
first three months experienced exceptionally high monthly rainfall. The new situation prompted for a decision to
re-adjust to an Average HYC from April 2004 for the remainder of the reporting
period. Another flood of magnitude
25.39 m3/s (4.43 MCM) was released for two days from 18-20 August
2004.
The IFR release target of 67.54 MCM for the period
amounts to 12.17% of the 554.8 MCM long-term MAR at Katse dam. The actual
volume released from Katse Dam was 47.67 MCM. This translates into a shortfall
of 29.42% against target. The long-term
target release of 67.13 MCM for Katse is 12.1% of the MAR. It is evident that
the 2003/04 year fell 29% below that long-term target. The inflow to Katse in
the same year was approximately 35% below average at 361.44 MCM. The actual
release of 47.67 MCM therefore constituted 13.2% of the actual inflow.
The flow volume recorded at IFR site 2 amounted
to 63.65 MCM. The target IFR volume was maintained at 91.41MCM, resulting in a
deficit of 30.4%. This is misleading to
some extent, however, since the target is the target for an Average
hydrological year, the targets at site 2 having not been computed for the other
scenarios.
The discrepancy would thus be lower if the
target was pegged to each month’s hydrological classification (as per column 2 in Table 2-6).
Figure 2‑2: Actual vs.
target releases from Katse Reservoir for the hydrological year 2003/04 (Source: LHDA-a, 2005)
NOTE:
The target releases shown here do not include floods; they reflect only target
low flows.
No spillage occurred at the Katse Dam for the
reporting period. Floods at IFR site 2 were assumed to be coming from the dam
and/or from incremental catchment flow, notably from the Khohlonts’o tributary
which enters the Malibamats’o just above IFR site 2.
It is evident from Figure 2-2 that the February
flood was not delivered to IFR site 2 by either the catchment inflow tributary
or by a scheduled release from the dam as the recorded flow remains constant
throughout the month.
The actual flow curve recorded downstream at
IFR site 3 (Paray), which is below the confluence with the Matsoku River, shows
that a flood came down the Matsoku River in February (see column 7, Table 2-5).
Also noteworthy is the fact that targeted and
actual monthly dam low flow releases show very little variation, and are
constant. This must be partially attributed to the limitations on the
compensation valves and flood release mechanisms at Katse, which resulted in
IFR schedules with limited variability in low flows.
Table 2.4: Katse
Dam monthly releases - October 2003 to September 2004
|
Month
|
Inflow MCM/# Hydrological Year classification
|
Target Dam Releases*
MCM
|
Actual Dam Releases**
MCM
|
IFR Site 2 Target Volume
MCM
|
IFR Site 2
Actual Volume
MCM
|
IFR Site 3
Actual Volume
MCM
|
|
Oct-03
|
7.44 /Plus
1
|
2.95
|
@3.63
|
5.05
|
5.06
|
4.73
|
|
Nov-03
|
15.08 /Plus
1
|
13.60
|
3.01
|
16.80
|
4.57
|
5.84
|
|
Dec-03
|
20.72 /Plus
1
|
3.21
|
3.22
|
7.00
|
4.47
|
4.79
|
|
Jan-04
|
60.56 /Minus
1
|
7.70
|
2.74
|
10.56
|
4.39
|
8.71
|
|
Feb-04
|
82.88 /Minus
1
|
(3.08 + 9.0)$12.08
|
3.43
|
16.67
|
5.17
|
19.62
|
|
Mar-04
|
105.14 /Minus
1
|
2.95
|
2.95
|
5.78
|
5.00
|
16.64
|
|
Apr-04
|
54.29 /Average
|
7.74
|
5.94
|
9.90
|
4.93
|
12.79
|
|
May-04
|
7.11 /Average
|
3.21
|
8.60
|
3.98
|
10.18
|
10.58
|
|
Jun-04
|
5.24 /Average
|
2.85
|
2.84
|
3.44
|
4.76
|
8.35
|
|
Jul-04
|
0.78 /Average
|
2.41
|
2.42
|
2.69
|
3.84
|
5.12
|
|
Aug-04
|
1.17 /Average
|
(2.14 + 4.5)£ 6.64
|
6.58
|
6.75
|
7.65
|
7.37
|
|
Sep-04
|
1.03 /Average
|
2.20
|
2.31
|
2.79
|
3.63
|
7.97
|
|
Total
for Year
|
361.44
|
67.54
|
47.67
|
91.41
|
63.65
|
112.51
|
Source: “Instream Flow Requirement (IFR): October 2003 to September 2004”,
Hydrology Branch of the Operations Maintenance and Engineering Group (OM&E
Group), LHDA, January 2005, hereafter cited as LHDA-a, 2005; and OM&E
Group, miscellaneous data supplied directly, February 2005.
Mohale Dam releases - January
to September 2003
In the case of Mohale dam, IFR Policy and
Procedures commenced from August 2003 as a result of satisfaction of the
requirements of the Washington Agreement with the World Bank.
Table 2‑5:
Mohale Dam releases - January 2003 to September 2003.
|
Month
|
Hydrological Year Classification
|
Mohale Release Target Volume
MCM
|
Mohale Release Actual
MCM
|
Marakabei (IFR site 7)
Flow Volume
MCM
|
Monthly Ave Inflow (Rainfall-Runoff
Model)*
MCM
|
Mohale Inflow (Water Balance Model)
MCM
|
|
Jan-03
|
Transitional to inundation: Releases
were as per Washington Agreement
|
6.56
|
8.82
|
8.40
|
39.9
|
33.44
|
|
Feb-03
|
5.93
|
4.87
|
4.18
|
44.9
|
25.99
|
|
Mar-03
|
6.56
|
4.89
|
8.03
|
41.4
|
87.23
|
|
Apr-03
|
6.35
|
4.62
|
6.26
|
33.0
|
21.04
|
|
May-03
|
6.56
|
7.61
|
8.16
|
15.3
|
3.76
|
|
Jun-03
|
6.35
|
7.91
|
9.16
|
8.4
|
0.65
|
|
Jul-03
|
6.56
|
6.14
|
6.94
|
7.6
|
1.04
|
|
Aug-03
|
Plus
1
|
5.37
|
2.10
|
2.85
|
9.7
|
3.69
|
|
Sep-03
|
Plus
1
|
1.94
|
1.43
|
2.11
|
11.2
|
3.34
|
|
TOTAL
|
|
52.18
|
48.39
|
56.09
|
211.40
|
180.18
|
|
Oct
|
Reported
in Table 2-6 for year 2003-2004
|
27.4
|
6.97
|
|
Nov
|
37.3
|
12.76
|
|
Dec
|
30.1
|
8.77
|
|
Total
|
|
|
|
|
306.2
|
201.71
|
Source: Data supplied by OM& E Group, LHDA, February 2005
* Data derived from
long-term hydrological model used for the IFR studies. They are included simply
to illustrate the long-term average
expected runoff in the system, as a comparison against the calculated actual
inflows.
Mohale Dam releases - October 2003 to September 2004
Mohale Dam commenced the year under
the Average hydrological year class conditions. However, for the period January
- March 2004 the HYC was re-classified to Minus 1 in response to the dry
conditions in the preceding months. These three months experienced high
rainfall and the HYC was reclassified again to Average from April 2004.
The total released amount of 37.56
MCM for the period was effected through the operation of either a 500mm
diameter sleeve valve or a 200mm diameter sleeve valve. The amount was 37%
higher than the target release of 27.36 MCM. Higher releases were made from the
dam to reduce the deficit that was accumulating in the flow past IFR site 7 (see Table 2-6), as per the IFR Policy.
It would appear that inflow that was
expected to be contributed by the incremental catchment between the dam and IFR
site 7 had been over-estimated. The
estimate was based on the relative catchment areas. The IFR policy makes provision for scheduled dam releases to be adjusted
in such circumstances and the authorities authorised increased releases from
March 2004. They decided not to amend
the IFR Procedures however until a longer record was available to analyze.
At the same time, only one of the
two scheduled flood releases were effected as planned, that in August
2004. However, a lot of water was
released in April and again in June to reduce the accumulating deficit at IFR
site 7. No spilling was expected or
occurred from Mohale Dam because it was still filling.
The water volume flow recorded at
IFR site 7 for the period was 49.31 MCM against a target of 70.12 MCM, a 30%
total deficit over the year, for the reasons explained above. Figure 2-3 reveals the patterns in target
versus actual releases from the dam as well as target and actual flows at IFR
site 7. The following observations can
be made:
Ø
Targeted releases show more pronounced
variability, a demonstration of a healthy state of condition.
Ø
Actual releases showed acceptable variability,
except as regards the timing of flood flows;
Ø
Recorded flows at site 7 closely follow the
volume of releases from the dam, except for exceptionally high flows. This
suggests that the incremental catchment contribution to base/ low flows was
negligible, the major contribution being from the released floods.
Ø
Late summer/ autumn rains raised flows at site
7 very substantially (blue line in Figure 2‑3 in the months Feb, March)
indicating the appropriateness of the April flood release.
The notable discrepancy in target
versus actual at IFR sites 2 and 7 has focused attention on the need for a
reappraisal of the flows from the incremental catchment to the IFR sites. The
IFR Consultants have advanced the case for a review of this input based on
empirical data. Their advice has been accepted and such verification is planned
to occur in the coming year.
Table 2-6: Mohale Dam
monthly releases - October 2003 to September 2004 (Source: LHDA-a, 2005; and OM&E Group, miscellaneous data supplied directly,
February 2005)
|
Month
|
Inflows
to Mohale/ Hydrological Year classification
|
Target Dam Releases**
MCM
|
Actual Dam Releases
MCM
|
IFR Site 7 Target Volume
MCM
|
IFR Site 7
Actual Volume
MCM
|
|
Oct-03
|
/Average
|
2.00
|
1.86
|
6.88
|
2.64
|
