Flooding - Drainage Basins Flashcards
what is the basic role of streams and rivers within the Earth system?
drain water off the landscape and transport sediments
how does flood happen?
when stream overflow its banks owing to the sheer amount of water flowing from the landscape and into the stream
why is there a tendency of large number of people and buildings to be at risk of flooding?
1.) humans concentrate their settlements along waterways
2.) relatively frequent nature of flooding
these tend to cause increased development in area that previously had been avoided due to frequent flooding
use of engineering controls
these tend to cause increased development in area that previously had been avoided due to frequent flooding
use of engineering controls
formula for discharge
volume (ft^3) / time (s)
how do you get the volume of a discharge?
multiply cross sectional area of the stream to its average velocity
how do you get cross sectional area of a stream?
length x average depth
how do you get average velocity of a stream?
using an empty plastic bottle, timer, and a measuring tape
the velocity of a stream is greater along the _______ because it has ________ friction
center ; lesser
described as the volume of water moving through a channel over a given time interval
stream discharge
a process where water flows through stream channels
runoff
precipitation reaching the land surface moves downslope in thin sheets
overland flow
these allows water to return back to the atmosphere
evaporation and plant transpiration
discharge of groundwater into the surface environment
groundwater baseflow
the volume of water moving through a channel
stream discharge
t or f: frequency of flood increases due to climate change
t
provide information about a river or a stream by simply plotting the discharge versus time
stream hydrographs
stream hydrographs is a function of:
discharge and time
the amount of time for water to move across the landscape and into channels
lag time
lag time is a function of
distance between where the rain is falling to the particular channel where discharge is being measured
this allows streams in man areas to have a continuous input of groundwater at some minimum level
baseflow conditions
keeps streams from going dry between rain events, thus is critical in maintaining the health of stream ecosystems
groundwater baseflow into streams
___________ allows more water to infiltrate to the water table which causes the water table in _______to be higher than the ________, thereby forcing groundwater to flow into streams, this is referred to as ___________-
high precipitation ; humid regions; stream channels; gaining streams
are a result of less deep infiltration in arid areas resulting in water table that is below the level of most stream channels
losing streams
useful tool in analyzing how stream discharge changes over time
stream hydrographs
a network of stream channels where merging tributaries form progressively larger streams
drainage system
smaller of any two merging channels
tributary
larger stream that serves as the principal channel within a drainage system
river
the upper portion of the drainage system
headwaters
found in the lower part of the system where a river empties into an ocean, lake or another river
mouth
t or f: headwater streams are generally small and relatively fast moving
t
headwater streams occupy ______ ; the mouth have gently flowing river that occupy ________
narrow valleys ; wider valleys
individual systems are separated by one another by a
drainage divide
a drainage divide is a
topographic high or crest in the landscape ; ridge
useful for mapping what hydrogeologist call the drainage basin
drainage divides
represents the land area that collects water for an individual stream or river
watershed or drainage basin
t or f: rainfall can cause flooding in one basin but have yet no impact on stream discharge in adjoining basin
t
t or f: as streams go downhill, they merge and form progressively larger streams and rivers
t
the high ground separating different drainage networks
drainage basin
top ten largest rivers in the world based on discharge
- Amazon
- Congo
- Ganges
- Yangtze
- Orinoco
- Parana
- Yenisey
- Mississippi
- Lena
- Mekong
what continent has the most number of largest rivers?
Asia
an area on a map outlined by a divide is known as
drainage basin
t or f: a drainage basin can be large or small
t
two major river basin in mindanao:
1.) Mindanao River Basin
2.) Agusan River Basin
provinces that the mindanao river basin covers
Bukidnon, Maguindanao, North Cotabato, South Cotabato, Sultan Kudarat
regions that the mindanao river basin covers
X , XII, ARMM
cities that mindanao river basin covers
Cotabato City, Korondal
total land area of mindanao river basin
21,503 km^2
second largest river basin in the Philippines
Mindanao River Basin
largest river basin in the Philippines
Cagayan River Basin
total land area of Cagayan River Basin
27,493.49 km^2
a stream flowing away from the mainstream due to sediment influx
distributary
any smaller stream that feed larges streams within a drainage basin
tributaries
a method of classifying or ordering the hierarchy of natural channels
Strahler Stream Order
stream order is regionally controlled by
topography and geology
t or f: a high number of strahler stream order means the stream is larger
t
reflects the downstream trade off between discharge and slope in setting transport capacity
Stream Longitudinal Profile
the ability of a stream to move sediment and incise rocks
sediment transport capacity
t or f: steep gradient and changes in slope results in high flow velocity thus, high transport capacity
t
variables of a stream longitudinal profile
elevation and river length
the level below which a river or stream cannot incise or erode
base level
the level where the velocity and eroding power of the water is temporarily lost, it lies in topographic laws that are relatively still elevated
local base level
examples of local base levels
marshes, swamps, lake, dam, watefalls
this is the ultimate (absolute) base level for most streams
global sea level
quantity of average sea level rise in the Philippines
3 to 4 mm/yr
quantity of average sea level rise in Davao
2 to 3 mm/yr
t or f: absolute sea level is zero meters above sea level
t
this is defined as total stream channel length divided by the area of the drainage basin
drainage density
a stream longitudinal profile can be generated in GIS through:
DEM and line feature
what does a small break value in delineating drainage system in GIS mean?
high channel length, more stream features delineated
drainage density is approximately equals the inverse of the
source basin length
________ tends to be highly dissected and thus have a high drainage density
steep terrains
_________ tends to be less well dissected, with substantial hillslope convexities and low drainage density
gentle terrain
examples of steep and gentle terrains
steep : flanks of volcanoes
gentle: flood areas/ plains
what forms braided and anastomosing streams?
high sediment influx than surface runoff
