Drainage basins

drainage basin

extent of land where all surface water from precipitation converges to a single discharge point

how do you delineate a drainage basin

using the contour elevation lines on a map

what are the nine components of a drainage basin

1. rides/divides

2. gullies

3. ephemeral channels

4. floodplains

5. perennial channels

6. soil

7. hillslopes

8. vegetation

9. aquifers

a drainage basin is a topographic region from which a stream/rive receives______

• runoff

• throughflow

• groundwater

runoff vs throughflow

runoff - surface processes

throughflow - infiltrated water that moves to river

how can drainage basins be identified on a map

by tracing a line along the highest elevations between two areas

what are the two longest rivers in NA and what watershed are they the backbone of

Mississippi and Missouri River

backbone of Mississippi watershed

how many major watersheds are in Alberta

7

what is Lethbridge’s main watershed and sub-basin

main watershed - S Sask river watershed

sub-basin - Oldman River Sub-basin

contrast homogeneous vs heterogeneous drainage basins

homogeneous - consistent and uniform properties throughout its area

heterogeneous - has properties that vary significantly in different locations

are small drainage basins typically homogeneous or heterogeneous? large drainage basins?

small - homogeneous

large - heterogeneous

what are independent variables that can change throughout a drainage basin

elevation, slope, vegetation, land use, climate

gross drainage basin

the total area of a drainage basin enclosed by its drainage divide

effective vs dead drainage area

effective - the area expectant to contribute to runoff during precipitation event

dead - there is no outflow of an area even under wet conditions

what is the gross drainage area of the Oldman River sub-basin? effective drainage?

gross - 27 500 km²

effective - 76% of gross

what are landforms/conditions that might reduce effective drainage area

• soil is dry = increases water infiltration

• dams/diversions

• reservoirs

• evaporation

what are the 7 physical characteristics that affect drainage of drainage basins

• size

• morphology (shape/length)

• land slope

• soil type/moisture

• Drainage density

• vegetation/land use

• bedrock lithology

drainage of small vs large watersheds response to storm events

small - flashier response (faster)

large - higher storage capacity

do larger or smaller basins have steeper hydrograph?

smaller = steeper

larger = flatter

what shaped basin will produce a flat hydrograph

elongated (thin and long)

what shaped basin will produce a peaked hydrograph response

rounder basins

which shaped basin drains faster? longer?

rounder basins - faster

elongated - longer

what does the slope of the watershed govern

how fast water will drain to the channel

steep slopes vs gentle slopes hydrograph response

steep = peaked response

gentle = flat response

what is the gradient for a steep slope? gentle slope?

steep - 5% or more

gentle - less than 1%

which soils will have quicker infiltration?

sandy soils

which type of soil contributes less to streams? more to streams?

less - sandy soils

more - clay soils

why do clay soils contribute more to basins

because they soak up less water

do saturated or dry soils contribute more to streams

saturated - more to streams

dry - less to streams

what does the drainage density measure

the total length of all streams on a map and dividing by watershed area

High DD vs low DD

high - peaked hydrograph response (quicker drainage to basin)

low - flat hydrograph response (longer to drain)

cement parking lot vs grassland vs forest influence on drainage basin’s ability to drain

cement - no infiltration = rapid drainage

grassland - higher infiltration - slower drainage

forest - trees intercept precipitation - slower drainage