2. Watersheds and hydrologic systems Flashcards
Landscape
- A mosaic of ecosystems that are interacting
- An area that is spatially heterogenous in at least one factor of interest
Watershed
- The land area that drains water to a particular stream, lake, or river
- An area of land from ridge top to ridge top that collects, stores, and releases water to a common point (called outlet) such as a river point or lake point
Synonyms of watershed (3ish)
- Basin (water basin or river basin)
- Catchment (catchment basin or catchment area)
- Drainage area
Basins are typically what types of watersheds?
A very large watershed
Catchments are typically what types of watersheds?
Smaller watersheds
How do we identify watersheds (2 elements) ?
- The divide is a ridge or a strip of high ground that separates one drainage basin from another
- The outlet is the outflow point of the watershed
Stream
A stream is a body of running water that is confined in a channel and moves downhill under the influence of gravity
Tributary
A tributary is a small stream flowing into a larger one
Headwaters (of a stream)
The headwaters of a stream are the upper parts of that stream near its source in the mountains
Stream order rules:
An order 1 stream meets another order 1 stream
Order 2 stream
Stream order rules:
An order 2 stream meets another order 2 stream
Order 3 stream
Stream order rules:
An order 1 stream meets an order 2 stream
Order 2 stream
How do we draw a watershed (3 steps)
- Identify the outlet point
- Identify high-elevation points surrounding the waterbody
- Link the high-elevation points by crossing contour lines at right angles (the line drawn is the watershed divide)
What can make a difference in delineating watersheds?
(2 elements that can be “forgotten”)
1) If we don’t consider groundwater
- the surface water catchment divide can be different than the groundwater catchment divide
- i.e. maybe there is infiltration which will make some of the water that would normally run down one side of the hill, run down the other side
2) If we don’t consider human landscape features (e.g. reservoirs, roads)
- e.g. a reservoir could trap lots of water and for a significant amount of time, such that the water evaporates before it can make it to the outflow point
- so like maybe this water would no longer be part of the watershed
Water body (def + characteristic)
- Any stream , river, pond, lake, estuary, ocean, or other body of water
- Water bodies can be flowing (lotic) (e.g. river) or non-flowing (lentic) (e.g. wetland or lake)
- Flow of water is greatly affected by topography, slope, soils, and vegetation
Riparian zone
- The non-cultivated vegetated land that touches and immediately surrounds a body of water
- Often includes wetlands
- Riparian = of the river
(- they are critical ecozones)
Flood plain (def)
The flat area of land surrounding a water body that is subject to periodic flooding
Flood plain roles (4)
- holds excess water after precipitation events
- filters out sediment
- provides habitat for wildlife
- provides recreation for humans
Upland area (def)
- Area of land at a higher elevation above a water body
- It forms the last sub-unit before the watershed boundary or divide
Upland area roles (4)
- provides habitat
- stabilizes soil
- minimizes soil erosion
- filters surface runoff
Watershed characteristics that can be computed (4, but with subcategories)
- Elevation → min, max, mean, median & standard deviation
- Slope → min, max, mean, median & standard deviation
- Land use and land cover proportions → % agricultural, % forest, % urban
- Morphometric variables (e.g., watershed area, perimeter, circularity, elongation)
- Drainage-related variables
Stream drainage density equation
Drainage density (Dd) = sum of all streams and river lengths / watershed area
→ unit for e.g. km/km^2 → km^-1
Factors controlling drainage density (6)
- morphometric variables
→ Dd ↓ when watershed area ↑
→ Dd ↑ when average watershed slope ↑ - geology
- climate
- vegetation
- time
- human impacts
Three main watershed functions
- Collection of matter from external sources (e.g. capture of precipitation water)
- Storage of matter (water, sediments, nutrients, etc.) in variable quantities for a variable amount of time
- Release of matter at different rates (e.g. discharge)
Two additional watershed functions
- provides diverse sites for biogeochemical reactions
- provides habitat for plants and animals at multiple scales
Stream roles within watersheds (4)
- sources
- sinks
- transformers
- filters
Watershed function: COLLECT
→ deeper def/function
- Water is transferred from atmosphere and is captured in the soil
- It can infiltrate through the soil surface and percolate downward into the soil profile
Watershed function: COLLECT
→ what can collect? (3)
- Geology (mountains, valleys, etc.)
- Vegetation (interception)
- Manmade surfaces
Watershed function: STORE
→ deeper def
Water is stored in the pores (air spaces) between soil particles in the soil profile
Watershed function: STORE
→ what can store? (7)
- wetlands
- lakes
- reservoirs
- groundwater
- snow + ice
- biology
Watershed function: RELEASE
→ deeper def
Water moves underground, through the soil profile, or across the land surface as runoff
Watershed function: RELEASE
→ what can release? (4)
- streams & rivers
- groundwater
- evaporation
- human engineering
