The law of 3 August 2018 introduces the “urban rainwater management” competence as a separate competence from sanitation, which becomes mandatory on 1 January 2020 for conurbation communities.

In order to guarantee the operationality of a genuine community rainwater management service, the Agglomeration must be in a position on 1 January 2020 to :

• Deliberate on a service regulation
• Determining means and an appropriate budget envelope
• Clarify the perimeters of intervention with the communes
• Define the management methods for this competence
• To have a clear vision of the works associated with the competence, the functioning of the rainwater system, the associated risks and stakes

It is in this perspective that the DLVA wanted to be assisted in clarifying the scope and methods of exercising the “rainwater” competence, in defining the methods of financing this competence and then in translating the doctrine desired by the urban area into operational documents.

Rainwater is defined as that part of the run-off that is managed by dedicated devices. It constantly interacts with groundwater and other networks. This partly explains the difficulties related to its management.

So-called run-off water is the part of the flow that is not managed by dedicated devices.

Rainwater and run-off water are therefore two sides of the same water that circulates on and through the city.

Moreover, this skill covers a large number of works of various types (drain cover), underground networks, trench, etc.).

Finally, apart from structural works, local authorities and especially small municipalities have very little information on these works and do not include them in municipal budgets.

Article L2226-1 of the CGCT defines jurisdiction as follows:

 “The management of urban rainwater corresponding to the collection, transport, storage and treatment of rainwater from urban areas constitutes a public administrative service under the responsibility of the municipalities, called the public service of urban rainwater management”.

The rainwater competence integrates 3 dimensions:

• the “geographical” scope of exercise of the competence
• the content of the competence: the missions carried out, the actions carried out
• the heritage concerned (the works)

In order to best define the rainwater competence, it is necessary to go through a certain number of steps that allow this mission to be carried out successfully. One of the key issues is the determination of the network linear. It is thanks to this that it is possible to make an estimate of the number of structures present on the network and thus deduct the financing to be planned.

In order to determine the network’s linearity, it was necessary to cross-reference 4 data sources:

• Linearity of the communal and departmental road network in urban areas and areas to be urbanised
• Linearity of the collective sewerage network
• Comparison with street lighting
• Estimation in relation to the geo-referenced rainwater network / urban surface to be urbanised

The definition of the line of sight thus produced the following result: 329 km of main rainwater network (314 in the municipalities and 15 in the business parks), excluding secondary ramifications. It includes 6,567 storm drains and 8,246 manholes.

The competence in stormwater management is at the centre of several other public services and thus creates very strong interactions between services. The opinion of each service is all the more important in order to define the best decision that suits the different visions and major issues of the territory.

Given the financial and organisational issues at stake (municipalities and conurbation), Altereo has deployed a specific coordination strategy in order to build a consensus between the elected officials & technicians as well as between the conurbation and its member municipalities.

Throughout these meetings, a real decision-making support method was put in place:

• Understanding of the stakes for everyone
• Provision of factual and pragmatic elements
• Debate to finally arrive at a common idea

It is this sustained rhythm of meetings coupled with the pooling of various actors, with different cultures, that has enabled the Durance Luberon Verdon conurbation to make a quick decision as to whether or not to take over the management of the rainwater management competence on its territory.