drainage basins

Question 1

what is transpiration and what is it limited by?

Answer 1

biological process by which water is lost from a plant through its pores, and is limited by the availability of water in the soil

Question 2

what causes water to be drawn up towards the surface during drier periods

Answer 2

capillary action

Question 3

list and explain 4 factors that effect the rate of infiltration in soil

Answer 3

• amount of water already in the soil
• porosity and structure of the soil
• nature of the soil (ploughed, cracked, crusted…)
• amount of seasonal changes in vegetation cover

Question 4

water lying on the surface is called?

Answer 4

surface storage

Question 5

when rainfall is intercepted by vegetation, list and explain 3 possible routes that it can reach the underlying soil

Answer 5

throughfall - water dropping of limbs and leaves
stemflow - water running down the trunk
secondary interception - undergrowth

Question 6

in what areas will you find surface runoff to be the highest and why

Answer 6

in urban areas, which have impermeable coverings of concrete, tarmac…

Question 7

what is infiltration capacity?

Answer 7

maximum rate at which water can pass through the soil

Question 8

what do we call rain that falls directly into the river

Answer 8

channel precipitation

Question 9

list 4 ways in which water reaches the river

Answer 9

channel precipitation, surface runoff, throughflow and baseflow

Question 10

what does a hydrograph do

Answer 10

shows the response of a river to rainfall by showing the rivers discharge at a given point over a short period of time

Question 11

what is discharge

Answer 11

amount of water that originates as precipitation which reaches the channel

Question 12

what do we call the period when the river is at its highest

Answer 12

peak flow

Question 13

what do we call the period when the river level decreases, and why is this segment less steep than the rising limb

Answer 13

the falling limb, less steep because because throughflow is being released generally slowly into the channel

Question 14

by what means do rivers maintain flow during periods of low precipitation

Answer 14

baseflow is very slow to respond to a storm, and continually releases groundwater to maintain the rivers flow during periods of low precipitation

Question 15

what is discharge measured in?

Answer 15

cumecs

Question 16

what is lag time?

Answer 16

period between peak precipitation and peak discharge

Question 17

what influences lag time

Answer 17

conditions within a drainage basin, such as soil and rock type, slope and size of basin, drainage density, type and amount of vegetation and also amount of water already in storage

Question 18

how does basin size, shape and relief effect the hydrograph of a basin

Answer 18

• Size - if its small, rainfall will reach main channel faster than a larger basin
• Shape - circular basin will have a shorter lag time than an elongated basin
• Relief - slopes and valley sides effect lag time, the steeper the faster

Question 19

explain how precipitation types will effect the drainage basin differently

Answer 19

• prolonged rainfall - long period of heavy rainfall, ground becomes saturated and infiltration is replaced by surface runoff
• intense storms - heavy rain could have greater intensity to infiltration meaning more surface runoff and rapid increase in river size

Question 20

explain how temperature effects infiltration

Answer 20

extreme cold and heat can restrict infiltration and increase infiltration. if transpiration rates are high then less water will reach the channel

Question 21

how does rock type effect a hydrograph and movement of water in soil

Answer 21

permeability of the available rock will define whether water will pass through the ground

Question 22

soil type and its effect on a hydrograph

Answer 22

controls the rate and volume of infiltration, moisture storage and rate of throughflow.
sandy soils with large pores allow rapid infiltration
clays have small pore spaces reducing movement

Question 23

how does drainage density effect the hydrograph?

Answer 23

density is higher on impermeable rock and is more prone to flash floods

Question 24

what is morphometry?

Answer 24

measurement of shape and form

Question 25

explain law of stream number in a drainage basin

Answer 25

unbranched source tributaries are first order streams

when two first orders join they form a second order stream. and so on… need 2 equal order streams to move up in order

Question 26

what do we call the point at which 2 streams meet

Answer 26

confluence

Question 27

what is the bifurcation ratio

Answer 27

relationship between the number of streams of one order and that of the next highest order