Denbow: How does soil help with stormwater management?
Tom: Soil is an integral part of the stormwater management system. Our urban areas have many impermeable surfaces. Areas that include plants, turf and soil act as permeable networks within our cities and towns. The right type of soil will facilitate the water movement into either engineered drainage systems or continue the natural cycle into aquifers and such. The type of soil affects the retention and movement of water. Ultimately, a place like British Columbia gets a lot of rain. In an urban setting, rainfall must be managed. Facilitating drainage while promoting plant growth are key components of the hydrological cycle.
Denbow: Do we lose soil to erosion and washouts?
Tom: The soil should not wash away per se if it is the right soil. The right soil structure will help to manage moisture and resist erosion. Soil structure is part loam, clay and sand. Each has its role to play in keeping the soil together, while allowing the plant roots to grow freely and allowing for proper drainage. The right soil can resist erosion by way of it’s composition and will act as a filtration method to deal with stormwater.
Denbow: How does that act as a filter?
Tom: Soil by its natural make up will have pore space and is made up of different materials such as clay and organic matter. Each has a capacity to hold onto water for a period of time as well as extract nutrients, contaminants and particulate from the soil as long as the structure remains intact and is appropriate for its specific use.
Denbow: What’s important to know about soil as a stormwater management tool?
Tom: The right soil for the right place is an important consideration. Soil can either be an imported, engineered soil such as for a green roof or for bio swales. Or it could be the existing site soil. Either case requires proper testing of the soil to ensure it has the right properties to meet the needs of the specific application. Due diligence is required to determine that the soil continues to act as the natural filtration and water retention tool that it can be. The balance between the release of moisture and the retention of moisture is critical for maximizing the soil’s productivity and the correct soil will do both.