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Watershed Basics

What is a Watershed?

A clear, practical guide to how water moves across land—and why that matters for communities, habitat, and planning.

DefinitionHow it worksTypesWhy it mattersStewardshipFAQ

Definition

A land area that drains to a common point

A watershed is an area of land where rainfall and snowmelt drain toward the same place—such as a creek, river, wetland, or lake. Gravity moves water downhill through small channels that merge into larger streams and rivers. High ground—ridges and divides— separates one watershed from another.

Watersheds come in many sizes. Small local catchments nest inside larger basins. Mapping by topography, not by politics, means a watershed can cross municipal, provincial, and national boundaries.

How it works

From raindrop to river

1
Runoff
Rain and snowmelt flow overland into small channels (rills) that join to form creeks and rivers.
2
Infiltration
Some water soaks into soil, replenishing groundwater that slowly feeds streams and wetlands.
3
Storage
Wetlands, floodplains, and lakes store water, reducing peak floods and stabilizing flows.
4
Connectivity
Surface water and groundwater are linked; changes to one often affect the other.
Healthy watersheds balance runoff, infiltration, storage, and connectivity—the foundation for water security.
Watershed schematic showing divide, runoff, infiltration, storage, and channel flow
Schematic: divides, storage, infiltration, and channel flow.

Key Components

What makes up a watershed

  • Headwaters & Divides

    High ground that sheds water into different drainage areas; small streams begin here.

  • Streams & Rivers

    Channels that connect hillslopes to mainstem rivers, carrying water, sediment, and nutrients.

  • Wetlands & Lakes

    Natural storage that moderates floods and supports biodiversity.

  • Floodplains

    Low areas near rivers that spread and slow floodwaters, reducing downstream peaks.

  • Soils & Groundwater

    Subsurface zones that filter water, store it, and release it slowly back to streams.

  • Riparian Areas

    Vegetated streambanks that stabilize soil, shade water, and support habitat corridors.

Types

Open vs. closed basins

Open (Exorheic) Watersheds

Drain to the ocean through connected river networks. Most large river systems are open basins.

Outflow
To ocean
Connectivity
River → mainstem → sea
Example
South Saskatchewan

Closed (Endorheic) Basins

Retain water with no natural outflow; water leaves mainly via evaporation or infiltration.

Outflow
None
Water balance
Evaporation / infiltration
Example
Pakowki Lake

Both types can include wetlands, lakes, and groundwater—the difference is whether water ultimately exits the basin.

Why it matters

Water quality, habitat, and resilience

  • Clean Water

    Healthy watersheds filter pollutants and support safe drinking water supplies.

  • Flood & Drought

    Storage areas slow peak flows and sustain baseflows in dry periods.

  • Biodiversity

    Rivers, wetlands, and riparian zones provide critical habitat and migration corridors.

Human Influence

Urban & Agriculture

Impervious surfaces increase runoff; practices on fields and in towns influence sediment and nutrients. Storm sewers move water quickly, while compacted soils reduce infiltration and baseflow.

Human Influence

Restoration & Protection

Riparian buffers, wetland conservation, and smart stormwater design slow and clean water—stabilizing banks, filtering pollutants, and improving habitat connectivity.

Stewardship

Practical actions at home and work

  • Reduce Runoff

    Rain barrels, native landscaping, and permeable surfaces help water soak in.

  • Protect Riparian Areas

    Keep vegetation along streams; fence livestock from banks to prevent erosion.

  • Manage Nutrients

    Apply fertilizers carefully; maintain septic systems to protect groundwater.

Continue exploring

Watershed overview

Learn about SEAWA’s local watersheds and explore regional context.

Back to Watershed page