top of page

Water: resource or natural hazard?

Jun 24
5 min read

Water lies at the heart of contemporary environmental, territorial, and architectural challenges.

An essential resource for life, it is also the origin of some of the main natural hazards affecting our territories.

Droughts, runoff, floods, coastal inundation, and pressure on drinking water resources may appear contradictory. However, they are all manifestations of the same hydrological system, increasingly stressed by climate change and by transformations in land-use planning and urban development.

In this context, architecture can no longer consider water as a mere technical constraint. It becomes a structuring parameter of the project, from the territorial scale down to construction details.


The Breton paradox: a humid region facing water stress

We chose the Morbihan as a case study, as it is the territory in which we are based and one that clearly illustrates the alternation between winter abundance and summer scarcity.

The Morbihan receives on average between 600 and 1,200 mm of rainfall per year, depending on the area.

Despite this relatively high precipitation, the department regularly experiences water stress during the summer period.

This situation is explained by the region’s hydrological and geological characteristics, largely shaped by the Armorican Massif. This ancient geological base is composed of hard, fractured, and low-porosity rocks that do not allow the formation of large, deep aquifers capable of long-term water storage.

As a result, underground storage capacity is limited: groundwater tables are generally shallow, spatially restricted, and highly responsive to climatic conditions. During dry periods, they may recharge quickly but can also deplete within a few months.


In addition, the generally thin and poorly developed soils promote rapid runoff towards river networks. Water therefore quickly reaches streams and then the coastline, without constituting a durable territorial reserve.

In this context, Brittany—and the Morbihan in particular—relies mainly on surface water resources (rivers, reservoirs, dams) for drinking water supply, which increases the system’s sensitivity to seasonal variability.

The issue is therefore not the overall quantity of water available, but its ability to be retained, infiltrated, and redistributed over time.

 

One cycle, two risks

Drought and flooding are often studied separately. However, they result from the same imbalance in the water cycle.

During winter, the territory experiences water surplus conditions. Intense rainfall events quickly saturate soils, leading to multiple consequences:

  • increased surface runoff

  • overflow of drainage networks

  • river floods and inundation events

  • soil erosion

Water is present in large quantities, but it circulates too quickly. In coastal areas such as much of the Morbihan, these effects are further exacerbated by coastal flooding risks and the gradual rise in sea level.


In contrast, summer periods are increasingly marked by water shortages and more frequent droughts.

Groundwater recharge becomes insufficient, river flows reach more severe low-water levels, and pressure on drinking water networks increases.The territory is thus confronted with reduced water availability precisely when demand is often at its highest.


Urbanisation and the disruption of the natural water cycle

Drought and flood risks are not solely linked to climatic hazards. They are also amplified by territorial transformations, particularly the increasing impermeabilisation of soils.


In natural conditions, soil plays a fundamental role in regulating the water cycle. It absorbs part of the rainfall, filters water, temporarily stores moisture, and gradually contributes to the recharge of groundwater and river systems.

In contrast, impermeable surfaces—roads, car parks, roofs, and highly mineralised urban areas—significantly reduce these functions. Rainwater can no longer infiltrate naturally and is rapidly directed into drainage systems or watercourses through surface runoff.


In France, several tens of thousands of hectares of land are artificialised each year, progressively reducing the capacity of territories to absorb and regulate rainfall. Combined with the increasing intensity of rainfall events linked to climate change, this trend contributes to a higher frequency and severity of flooding.



sol perméable naturel
Example of permeable natural soil: water infiltrates

sol imperméable parking
Example of impermeable soil, water runs off and carries pollutants

The paradox is therefore clear: although rainfall is significant, water is evacuated so quickly that it no longer contributes effectively to soil recharge or groundwater replenishment.

This disruption of the natural water cycle generates a dual effect:

  • in winter, increased runoff leads to flooding and overflow events;

  • in summer, reduced infiltration limits groundwater recharge and increases water stress.

Thus, drought and flooding are not separate issues, but rather the two consequences of a single hydrological imbalance, to which urban planning and architectural design can provide concrete responses.


Designing with water: the role of the architect

Faced with these challenges, architects have concrete levers to support territorial adaptation. Their role is no longer limited to technical or regulatory compliance: it involves integrating the water cycle into the design process in order to reduce risks, preserve resources, and enhance site resilience.


1. Promoting infiltration at source

The first strategy is to restore water’s place within the territory by encouraging infiltration as close as possible to where rainfall occurs.

This includes the use of landscape swales, rain gardens, permeable surfaces, and the preservation of natural water pathways. By limiting soil impermeabilisation and slowing runoff, these measures reduce flood risk while contributing to groundwater recharge.

Landscape design thus becomes an integral part of architectural design.

The goal is no longer to evacuate water as quickly as possible, but to manage it locally using the site’s natural capacities.


2. Harvesting and using rainwater

Rainwater is also a local resource that can be mobilised for non-potable uses, such as:

  • outdoor irrigation

  • toilet flushing

  • cleaning and maintenance

As an indication, a 100 m² roof can collect approximately 60 m³ of rainwater per year in Brittany, depending on local conditions and system efficiency.

The objective is not long-term storage, but rather reducing potable water demand while limiting stormwater discharge into drainage systems.


3. Encouraging water efficiency

Sustainable water management also relies on reducing consumption.

The use of water-efficient fixtures, combined with a thoughtful approach to usage and rainwater harvesting, can significantly reduce a building’s potable water demand. In this context, architectural design decisions play a key role in ensuring overall performance and efficiency.

This approach offers a triple benefit: reducing operational costs, decreasing pressure on infrastructure, and preserving natural resources.

In the context of climate change and increasing resource scarcity, efficiency is no longer a constraint but a core design principle.


Water as a foundation of territorial resilience

Each project, regardless of scale, contributes to the overall functioning of the water cycle.

By promoting infiltration, reducing consumption, and integrating natural risks into design from the outset, architecture helps to:

  • reduce flood risk

  • alleviate water stress

  • preserve natural resources

  • strengthen climate adaptation

The architect plays a key role in redefining this balance.

Designing with water means simultaneously addressing resource management, risk mitigation, and resilience.

It transforms an environmental constraint into a design opportunity, contributing to the development of more sustainable territories better adapted to future climate challenges.


Sources:


 
 
bottom of page