Section 1 Flashcards
Definition of a Watershed
:The area of land that would drain surface
water towards a specific point on the
landscape or on a stream/watercourse
- Also called a “catchment
* The watershed is the fundamental spatial
unit, or control volume, that we use to
conduct hydrologic analyses
How to Manually Define or
“Delineate” a Watershed
- Water flows downhill!
- Need a topographic map or digital
elevation model - Pick a watershed “outlet”
- Identify stream channel/drainage
network (valleys) - Identify adjacent stream
channels/drainage networks - Identify high points (hills, ridges) that
are between the stream network you
are delineating and adjacent stream
networks - Starting at watershed outlet, draw
line connecting high points, making
sure to cross contour lines at right
angles (perpendicular)
‘S’ Variable in water component equation
- S represents soil
moisture storage and surface water
impoundments: - Typically assume DELTA S = 0 if conducting
water balances on an annual time step
Stage-Discharge Relationships significance and purpose
Defines relationship between water level in system and outflow rate
What to consider when operating on an anual time step
When operating on an annual time step
need to consider what an appropriate
“Water Year” should be:
* All snowfall should have melted (e.g.
October – September
Evaporation
Phase change of liquid water to
vapour from open water surfaces
Transpiration
Phase of change of liquid water to
vapour and movement into
atmosphere through plant
stomata
Evapotranspiration
Combination of evaporation and
transpiration
What is the groundwater in a watershed (check if this is correct)
Represents water recharging deeper geologic
systems not connected to surface water
What is the groundwater in a lake? (Check if this is correct)
- Represents water entering or leaving lake
through groundwater system - Quantification requires field
measurements (piezometers, seepage
meters, and/or numerical modeling)
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Runoff and Water Yield
Runoff (R) or Water Yield (Y) both describe the water that leaves the watershed at the outlet.
This includes:
Surface runoff , Interflow & Groundwater baseflow
Surface runoff
(water that flows over the land directly into streams/rivers)
Interflow
- water that moves through shallow soil layers before reaching a stream
- Interflow is lateral flow of water through the unsaturated zone to stream
Groundwater baseflow
Groundwater baseflow: water that slowly seeps into streams from underground aquifers
Baseflow is “Dry weather flow”, typically originating from groundwater or lakes/reservoirs
* Significant flow mechanism in perennial streams
* Baseflow Index (BFI) = Baseflow/Total Streamflow
Water Yield (Y) for a lake
refers to water entering the lake, usually through surface water features like rivers and streams.
This water can come from:
Watershed runoff (surface flow, interflow, and baseflow from surrounding land)
Direct precipitation on the lake
Groundwater inflow
Runoff vs. water yield
Runoff (R) is usually talked about in terms of watersheds, as it describes water moving over land.
Water Yield (Y) is a more general term that describes the total water available in a system (like a watershed or lake), including both runoff and subsurface flows.
Stream Network Indicies
Stream Network Indices
* Stream Order (or Strahler Number)
* Stream with no tributaries are designated 1st Order
* Confluence of two 1st order tributaries initiates a 2nd order stream and so on…
* Stream Order is correlated with watershed characteristics
Hyetograph
- Is a time series of
precipitation amounts
Hydrograph
-is a time series of
streamflow/discharge
Drainage Density
- Total Length of Streams / Catchment Area
Bifurcation Ratio
Related to stream order, ratio of number of streams within successive stream
order categories (e.g. # of 1st order streams / # of 2nd order streams)
Types of Hydrologic Data: Climate
- Precipitation
- Temperature
- Evaporation
- Solar Radiation
- Wind Speed
- Relative Humidity
- Hydrometric
- Discharge
- Level (Stage)
Types of Hydrologic Data: Hydrometric
Discharge
* Level (Stage)
What is prorating discharge for
Common practice to transfer
discharge records from gauged to
un-gauged watersheds
* Should ensure the watersheds
are hydrologically similar:
* Area
* Climate
* Topography
* Surface water storage
* Soils/geology
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