LESOTHO HIGHLANDS PHASE II has a core focus on community and the environment

After a long hiatus and planning preparation, construction on Phase II of the Lesotho Highlands Water Project (LHWP) is now well underway, central to which is the new Polihali Dam and transfer tunnel. IMIESA speaks to Tente Tente, Chief Executive of the Lesotho Highlands Development Authority (LHDA) – the LHWP’s implementing and management authority – about how experiences gained on Phase I have shaped the implementation of Phase II.

What were some of the key lessons learnt from Phase I?

TT Phase I, completed in 2003 and inaugurated in 2004, captured the attention of the world as one of the largest and most complex projects of its kind. It entailed the construction of major structures that include the Katse and Mohale Dams, as well as associated transfer and delivery tunnels that supply water to South Africa.

While Phase I was implemented with the required expertise and in line with internationally established standards, the realities of implementing a project of this magnitude and complexity for the first time brought many learnings. A prime example is that early and meaningful consultation with communities is crucial. Therefore, the groundwork for Phase II has been informed by Phase I and backed by extensive research. Baseline studies have included an assessment of the Instream Flow Requirements (IFR) encompassing water quality, flow and geomorphology aspects; the socio-economic conditions; fauna and flora; archaeology and public health. Environmental and Social Impact Assessments (ESIA) were also conducted, which were subjected to external independent review prior to the issue of environmental authorisations and records of decision by Lesotho’s Department of Environment.

Furthermore, the LHDA has established Area Liaison Committees (ALC) in all project-affected areas. They include representatives from the project, community leadership and community elected representatives. These structures serve to improve community participation in project activities and ensure an ongoing forum for issue identification and resolution.

The LHDA has introduced a robust project complaints management system, which integrates in-person and technological processes.

It closely monitors the management process to ensure that consultants and contractors effectively manage specific complaints relating to their work and people are given feedback. Every step is documented and recorded. Whilst these interventions have been effective to date, there will be a constant focus on improving partnerships with all communities during the life of the project.

How is compensation being managed for affected communities?

Under Phase II, consultations with affected households on compensation options have largely been completed, while registration of all assets that will be impacted has been finalised.

The LHDA has implemented alternative strategies to address compensation delays, which were a pain point under Phase I. One of the strategies – over and above this early consultation and registration of assets –is a phased handover of the construction sites to contractors, where assets that are required by contractors for preliminary works are acquired first, and only handed over to contractors after the affected households have been paid.

It must be noted that in cases where the project needs to access people’s properties before payment has been issued, the LHDA consults the specific owners of the affected properties, and an agreement is reached with them allowing the LHDA access to the land while payment is being expedited.

LHDA is pleased with the significant progress made in compensation payments for assets affected by the advance infrastructure projects under Phase II. Payments have also commenced for assets which will be affected by the Senqu Bridge, the Polihali Dam and Polihali Transfer Tunnel preliminary works. This is a major lesson learnt from Phase I that is directly being applied under Phase II and is showing benefit.

Does Phase II provide an opportunity to implement more sustainable land use?

Absolutely, and this is a crucial element since livelihood and land use activities in the LHWP catchments have a huge impact. For example, land degradation due to poor management of agricultural activities (crop farming and livestock grazing) affect the catchments and water sources that supply the reservoirs. Overgrazing on rangeland and wetlands and frequent soil disturbance due to poor cultivation methods lead to poor vegetation cover and increase the level of soil erosion and sedimentation in the reservoirs.

The LHWP Integrated Catchment Management (ICM) Implementation Plan was developed to address land degradation and livelihoods issues especially in Phase II of the project. The LHDA has intensified land rehabilitation and restoration activities to reduce soil erosion through improvement in vegetation cover and overall land management in the Polihali dam catchment.

The LHDA is concurrently studying the status of the wetlands in the Polihali catchment areas, especially those that are a priority for water delivery. The study will establish the rehabilitation needs of the wetlands and recommend appropriate rehabilitation measures that can be implemented even before impoundment of the Polihali Dam.

Phase I of the LHWP established protected areas at Bokong and Tšehlanyane. However, through biophysical studies of the Katse catchment, and during the development of the wetlands conservation strategy, it was realised that while Bokong and Tšehlanyane were important wetlands areas, they were not necessarily the priority wetlands for the Katse Dam. Hence, the wetlands studies of the LHDA have now focused on identifying wetlands that are a priority for water delivery for each of the reservoirs and on protected area establishment initiatives on such wetlands for Phases I and II.

What steps are being taken in terms of climate change?

The LHDA is currently implementing the contract to undertake the LHWP climate change vulnerability study and to develop the adaptation and mitigation plan.

The LHDA land rehabilitation and restoration activities implemented as part of the ICM implementation plan (e.g., brush control, reseeding, tree planting, establishment of protected areas, establishment of grazing associations, etc.) are meant to minimise the impacts of climate change on the catchments. Some of the main climate change elements are increased flooding (surface flow of water) and drought events.

The LHWP zones have a high concentration of peat wetlands. They are a specific type of wetland that play a particularly pivotal role in mitigating climate change. Peat wetlands hold some of the largest stores of carbon on the planet, and when disturbed or drained, they release the major heat trapping greenhouse gases, such as carbon dioxide (CO2) and methane (CH4).

Although peat wetlands make up only 3% of the planet’s land surface, they are said to absorb twice as much CO2 as all the world’s forests put together. Yet, despite their relevance for the global climate, wetlands are being destroyed faster than any other ecosystem. The LHWP’s

The impounding of the Polihali reservoir will submerge existing roads and tracks, affecting communities in the valleys and tributary catchments of the Senqu, Khubelu, Mokhotlong, Moremoholo and Sehonghong rivers. The three major new bridges being constructed – along with a network of feeder roads and the main access roads to the project area – all contribute towards minimising this disruption and helping to restore community access. Shown here is the Senqu Bridge site where excavations have started for the massive pier and abutment foundations necessary to support the new 825 m long and 90 m high bridge. This is the largest of the three in the LHWP Phase II programme contribution to peat wetlands rehabilitation and restoration therefore contributes to climate change mitigation and to improving the resilience of the nation.

As testimony to this, the ESIA for Phase II of the LHWP received an award from the Environmental Assessment Practitioners Association of South Africa (EAPaSA) as the Best ESIA in the region. This demonstrates the LHDA’s commitment to environmental sustainability.

What are some of the key technologies and the construction method employed for the Polihali Dam?

Polihali Dam will be a 166 m concrete face rockfill dam (CFRD). The dam embankment will be constructed in compacted layers from free draining rockfill, sourced locally in the Lesotho Highlands, very close to the dam. The main dam embankment will contain 15 million cubic metres of rockfill; and the 43 m saddle dam (also a CFRD) 1,25 million cubic metres of rockfill.

Due to the higher shear strength of rockfill compared to earthfill, side slopes can be steeper than earthfill embankments, resulting in less construction material and a shorter construction period. Using rockfill has a further advantage in that placement can continue during periods of heavy rainfall, frequent in Lesotho. That would not have been the case if the embankments were constructed from earthfill.

Polihali Dam was designed to be constructed in stages to allow overlapping of the major activities on the critical programme path, namely rockfill placement and concrete face slab construction. This method shortens the construction period and has a further advantage in that impoundment can be initiated during the construction period.

Are specialist concrete formulations required for the dam wall?

A number of site-specific factors have to be considered for concrete mix designs. The water at Polihali is “soft” making it moderately aggressive to concrete and this influences the required minimum binder content in mixes. Another important consideration is freeze/ thaw as temperatures at Polihali go down as low as minus 20 degrees Celsius during winter and during summer temperatures can rise to 35 degrees Celsius. Strict concrete specifications were therefore developed.

Concrete face slabs, considering the above factors, and because of low slump and good workability/durability requirements, require very specialised mix designs. Face slab concrete will be placed directly from mixer trucks into chutes running down the dam face onto a conveyor belt that delivers concrete onto the face before vibration/ compaction and finishing off. It is therefore important for concrete not to segregate down the chutes and due to the freeze/ thaw aspect mentioned above, air has to be entrained into concrete.

Fine and coarse concrete aggregates will be crushed from good quality basalt rock in a dedicated quarry on site. Experience in Lesotho has shown over the years that laumontite and smectite minerals in some basalt types can badly affect concrete quality and basalt containing these minerals is therefore avoided.

What type of tunnel boring machines (TBMs) are being used to establish the Polihali tunnel?

The unit employed is a double-shield gripper TBM designed to install and grout precast concrete segmental linings as it advances. Being a double-shield machine, the unit is able to simultaneously excavate the rock and erect the segments, with the machine fully protected by the shield. The tunnellers are never exposed to unsupported ground, and in effect never see the rock, except for the spoil emerging from the cutter head.

What are some of the key challenges and the expected monthly tunnel advance rate?

Given the existing system of LHWP tunnels, the general ground conditions are well understood, but with almost 1 km of rock cover in places, the particular conditions at a given location are uncertain. Key risks are faulted ground and water ingress, both of which are addressed through the robust design of the TBM and its backup system.

The Polihali Transfer Tunnel is 38 km long and the logistics of the two long TBM drives will be challenging: getting personnel and materials to the face, removing spoil and water, ventilation, power supply, and communications all require a substantial system behind the actual TBM.

Going into Phase II, the LHDA developed the Maloti Minnow Conservation Action Plan that promotes protection of this species and its habitats. This is Lesotho’s only endemic freshwater fish. The LHDA has undertaken minnow assessments across the country, and in the Polihali catchment has identified natural waterfalls on the Senqu and Moremoholo Rivers that were assessed and found adequate to act as natural barriers for the migration of predatory fish into the uppermost minnow habitats

Depending on the rock class encountered, the advance rate will be 30 m/day on a good penetration rate and 7 m/d on the worst penetration rate.

And in closing?

Once completed, Polihali Dam will create a reservoir on the Senqu and Khubelu rivers with a surface area of 5 053 hectares, adding some 2 325 million m3 in storage capacity to the LHWP scheme. This is crucial for water security and future regional water demand management, particularly within South Africa’s Gauteng economic region.

Phase II is equally important for Lesotho in terms of its macro and micro economic objectives, a prime example being a ramp up in hydroelectricity as a sustainable and constant power supply. Another is a renewed focus on sustainable land use and agrobusiness enterprise development within the areas that remain after the Polihali Dam has been impounded.

With slopes up to 12 m high, which included soft rock outcrops, creating a “soft” interface required the use of an undulating retaining system