Mauritius - PNQ: The Recent Flash Flood Was an Unprecedented Phenomenon Minister Bachoo says

The Vice-Prime Minister and Minister of Public Infrastructure, National Development Unit, Land Transport and Shipping, Mr. Anil Bachoo, statedin the National Assembly yesterday that the flash flood witnessed on Saturday 30 March 2013 was an unpredictable phenomenon, and that the intensity of rain registered demonstrates that never before, has Port Louis been subject to such a heavy downpour.  He was replying to the Private Notice Question of the Leader of the Opposition, Mr. Alan Ganoo.

According to the Minister, the Place d’Armes and the surrounding area are found on reclaimed land. Thus, the soil texture is such that it has a relatively very poor absorption capacity. Minister Bachoo said that the Motorway through Port Louis passing through the Place d’Armes was constructed in 1989. The outlet for surface water was towards the sea. In 1996 the Caudan Waterfront project was implemented. This private sector project is located between the Place d’Armes and the sea and is at a higher level. Within that project, the outlet to the sea was maintained by the construction of two underground drains. These outlets are maintained by the State Property Development Corporation.

High density

But this area is a densely built-up area, thus imposing serious constraints in terms of any sustainable infrastructure adjustment and upgrading, which adds to the problem.  Besides the subject side, i.e., Place d’Armes involves many stakeholders; the main ones being the Municipality of Port Louis and the State Property Development Company.

Moreover, following the flashflood which occurred on 13 February 2013, a survey was carried out by officers of the Ministry to identify the required remedial measures. Given the specificity of the site and the inherent constraints, it was found that a comprehensive study should be commissioned so that feasible and sustainable corrective measures could be applied.  For this purpose, an international consultancy firm Antonaropoulous & Associates together with Desai Associates has been assigned the consultancy services. The Consultant is required, inter alia, to draw up an inventory of existing drainage infrastructure, rivers, water crossings and other natural water course and assess the hydraulic properties and adequacy of the drainage systems.

However, upstream of the subject site, there are numerous works which have been undertaken in terms of upgrading of Canal Bissoon, Canal Anglais, Impasse Chalet in Vallée Pitot and upgrading of Canal Kitchri in Tranquebar. Works order were issued on 6th March 2013, the Minister further added.

New drains

Furthermore, the widening of the Motorway from Pailles to Caudan was undertaken as from September 2009.  The drainage system has been maintained and improved, where necessary, but not been reduced, Minister Bachoo underlined.  A total length of 3.0 km of new drains has been provided in the contract and existing drains along the sides at other places have been provided.  Four cross-drains at Montebello, Desbro, Bell Village and Cassis have also been provided. The dimension of the new drains is 700 mm x 700 mm and along the central verge, a circular drain of diameter 400 mm has been provided.

Roadside drains are designed for return periods of 10 years.  Under normal conditions, the drains on Motorway M1 operate normally.  However, on 30 March 2013, exceptional rain intensity was recorded. Water from the mountains poured into the Motorway in torrents.  No drain design or dimension would have catered for such a downpour, according to the Minister.  However, as soon as the rain receded, it was observed that the excess water was drained away through the existing drainage system very quickly.

Obstruction of Le Pouce stream

The water coming towards the site of works from La Poudrière canal and Le Pouce stream covers a discharge area of 16 square meters, the discharge area under the bridge at the site is 36 square meters. During construction of the piling works a flow well above the 16 square meters was maintained permanently. No overflow has even been observed at that site. However, Mr. Bachoo stressed that the Le Pouce stream is obstructed upstreams at the Jardin de la Compagnie and Chaussée where the discharge area is at a minimum.

Moreover, the Minister indicated that part of the Ring Road which has been completed is the first phase of the project which starts at Montebello and ends at Guibies. Its phase 2 has not been designed yet and will be part of the Public Private Partnership Road Decongestion Programme.

In August 2011, CCA Environmental (Proprietary) Ltd and Enviro-Consult Ltd, submitted a report on an Environmental Scoping Study for the PPP Road Decongestion Programme. The report was meant to provide the necessary EIA information to all bidders for consideration when the designs will be prepared.  This study concerned the Ring Road Lot 2 which starts with the Tunnel at Quoin Bluff and ends at Chateau d’Eau, the A1-M1 Bridge and the Harbour Bridge.

The objective of the report was to inform bidders of all environmental concerns which they have to take on board during their design and for the corresponding mitigating measures to be developed and included. The Road Development Authority will ensure that the necessary measures are duly captured in the design and construction of the Ring Road Phase 2.