Understanding Stormwater Management
Underground Stormwater Management System Installation.
Stormwater management is all about managing the water that comes from rain or melting snow. When it rains, water doesn’t just disappear. It travels across surfaces like roads, roofs, and grassy fields, collecting along the way. Without proper planning and systems in place, this water can cause serious problems. The goal of stormwater management is simple but crucial:
To prevent loss of life.
To minimize damage to property, assets, and infrastructure.
To protect the natural environment.
Stormwater management helps ensure that heavy rains or melting snow don’t result in flooding, erosion, or pollution. It’s about keeping people safe, protecting homes and businesses, and maintaining healthy ecosystems.
Natural stream in southern Ontario. Streams convey stormwater runoff and groundwater baseflow towards rivers, lakes, and eventually oceans.
What Is Stormwater?
Stormwater is the water that flows over the ground after a precipitation event, like rain or snow melt. When rain falls, it doesn’t soak into the ground everywhere. Instead, it can run off surfaces, creating what we call surface water. Engineers measure how much water flows off surfaces using a measurement called peak flow rate (Q), which is expressed in cubic meters per second (m³/s). This peak flow rate happens during a storm’s most intense moments, and managing it is one of the key challenges in stormwater management.
Stormwater flows must be managed carefully, using a combination of natural and man-made solutions. Without proper management, stormwater can overwhelm drainage systems, causing flooding, or carry pollutants into rivers and lakes, damaging the environment.
Stormwater Facilities: Natural and Designed
Stormwater is handled through systems that can either occur naturally or be built by people. These systems guide water away safely during and after a storm.
Natural Stormwater Facilities: Nature provides its own solutions for managing stormwater. These include:
Sheet flow (water spreading thinly over a large area)
Creeks, streams, and rivers
Ponds, marshes, and lakes
Oceans
Vegetated areas, like forests or grassy fields, also play an important role. Plants absorb rainwater, slow it down, and allow it to soak into the ground. The roots of plants also help water infiltrate deeper, replenishing groundwater supplies. Natural low-lying areas act as storage spaces for water, helping prevent flooding.
Designed Stormwater Facilities: In towns and cities, we need to build systems to handle stormwater. These include:
Swales and Ditches (shallow channels for water)
Inlets and catch basins
Storm sewers
Soak-away pits (areas where water can soak into the ground)
Stormwater management ponds
Outlets and outfalls (where water exits a system into natural water bodies)
Designed facilities work together to collect and temporarily store stormwater, reducing the risk of flooding and protecting the environment.
Excavation and installation of an urban underground stormwater management system.
Challenges in Urban Areas
In natural areas, rainwater behaves differently compared to urban areas. In natural landscapes, most of the rain is absorbed by plants or soaks into the ground. Only a small amount becomes runoff, and it travels slowly, causing little harm.
In cities, the situation is very different. Urban areas have a lot of hard surfaces like roads, parking lots, and buildings. These surfaces don’t absorb water, so most rain becomes runoff. This leads to several problems:
Higher flow rates: Water moves much faster on smooth, hard surfaces.
Higher surface water volume: More water becomes runoff because it can’t soak into the ground.
Quicker peaking: Water reaches its highest flow rate faster.
Less ground infiltration: Hard surfaces prevent water from soaking into the soil.
Depleted groundwater supplies: Without infiltration, groundwater isn’t replenished.
Because of these changes, urban areas are at a higher risk of flooding, erosion, and pollution. This is why stormwater management is so important in cities.
Stormwater Management as a Resource
Stormwater is viewed as a resource, not just a problem. By managing it carefully, we can make cities safer and healthier places to live. The best approach to stormwater management is one that strikes a balance:
Provide enough capacity to handle heavy storms without flooding.
Minimize the impact on the natural environment.
The ideal scenario is to keep all the stormwater within the same area where it fell, but this isn’t always possible. Instead, stormwater systems are designed to ensure that the amount of water leaving an area after development is no greater than it was before development. This principle is called post-development flow control and is a requirement in many municipalities.
Excavation and installation of an urban stormwater management system using rectangular plastic chambers.
Retention and Detention Strategies
Stormwater management systems use two main strategies: retention and detention.
Retention: This strategy reduces the volume, speed, and force of stormwater runoff by capturing and holding it. The systems store stormwater and release it slowly into the surrounding soil through infiltration. Retention helps prevent flooding and erosion, and it gives water time to soak into the ground. Examples of retention facilities include:
Soak away pits
Infiltration galleries
Detention: Detention systems store stormwater and release it slowly into the municipal sewers or local natural drainage system. These systems are designed to manage peak flow rates and prevent overwhelming drainage systems. Examples of detention facilities include:
Detention ponds with controlled outlets (wet or dry)
Underground storage tanks
Parks, sports fields, and parking lots that are designed to handle temporary flooding
Long, shallow swales and ditches
By combining these strategies, stormwater management systems can protect communities and reduce environmental damage.
Our Expertise at Everwest Engineering
At Everwest Engineering, stormwater management is our specialty. We’ve designed hundreds of systems for a wide range of projects, including:
Institutional (such as schools)
Commercial (such as warehouses)
Residential (such as apartment buildings, townhouse complexes, and single detached houses)
Our team understands that every site is unique, and we tailor our designs to meet the specific needs of each project. Whether it’s a small residential lot or a large commercial property, we take pride in creating systems that are efficient, cost effective, and environmentally friendly.
Stormwater management is not just about pipes and ponds; it’s about planning for the future and protecting our communities. At Everwest Engineering, we’re proud to be part of the solution.