Name:  _______________________________________________ Section:_______________________

part 2:  Surface Runoff and Erosion processes

1.   Figure 19.8 below shows a typical relationship between interception storage, infiltration and runoff during a storm event.  Using Figure 19.8, what is the rate of:

                                 After 20 minutes          After 100 minutes

      precipitation        5 CM/HR                     5 CM/HR

      interception         3.3 CM/HR                  0.8 CM/HR

      infiltration           1.7 CM/HR                  1.0 CM/HR

      surface runoff      0 CM/HR                     3.2 CM/HR

Figure 19.8  Relationship between precipitation, interception, infiltration, and runoff.  Note that the precipitation rate is a constant 5 cm/hr.

 

 

 

 

 

 

2.   Assuming Figure 19.8 is representative of the relationship between precipitation, interception, infiltration, and surface runoff for most conditions, what generalizations can be made regarding the change over the course of a storm event in the rate of:

a.   interception DIMINISHES AS FOLIAGE BECOMES SOAKED

b.   infiltration NONE WHILE SOIL STILL HARD AND DRY; RAPID WHILE MOIST BUT BELOW FIELD CAPACITY; DECLINES AFTER FIELD CAPACITY

c.   surface runoff NONE WHILE FOLIAGE INTERCEPTS; SLOW WHILE SOIL REMAINS BELOW FIELD CAPACITY; RAPID AFTER FIELD CAPACITY REACHED

3.   Figure 19.8 is a rather simple figure for displaying a complex set of relationships.  Identify two situations in which the relationships expressed in Figure 19.8 might not be completely true.

a. PRECIPITATION BRIEF OR INTERMITTENT (I.E., SHOWERS)

 

b. SOIL ALREADY SATURATED AT FIELD CAPACITY (E.G., BOG)

 

Since climate and vegetation patterns are related, there should be some correlation between rates of fluvial erosion, climate and vegetation.  Figure 19.9 shows the general relationship between runoff (a function of climate), erosion and climate. See also the water erosion vulnerability map (not the same as actual erosion, just the risk of it) and human-induced water erosion vulnerability map.

Figure 19.9  Relationship between runoff and erosion.  The erosion estimates are based on measurements of suspended sediment in streams.

 

 

 

 

 

 

4.   a.   What type of climate exhibits the highest erosion rate for the United States?

SEMI-ARID

b.   What two types of climates produce the highest erosion rates for the world?

SEMI-ARID AND EXTREMELY HUMID

c.   What biomes (ecological communities) are associated with the climates you listed in parts (a) and (b) that produce high erosion rates?

STEPPE GRASSLAND AND RAINFOREST

d.   What type of climate exhibits the lowest erosion rate for the United States and for the world? EXTREMELY ARID AND MODERATELY HUMID

e.   What biomes are associated with this climate producing low erosion rates?

HYPERARID DESERT AND TEMPERATE FOREST OR PRAIRIE

f.    Explain why these relationships exist.  Keep in mind that climate and vegetation are closely related to one another, and that both affect rates of erosion.

HIGH EROSION: 1) SPARSE VEGETATIVE PROTECTION AND OCCASIONAL PRECIPITATION; 2) SATURATED RAINFOREST FOLIAGE AND EXCESSIVE PRECIPITATION

LOW EROSION: 1) RARE PRECIPITATION; 2) DENSE VEGETATIVE PROTECTION AND MODERATE PRECIPITATION

5.   Fill in the tables below using Figure 19.10 to locate areas of high and low erosion rates.  Then use a world map of climatic regions and a world map of natural vegetation in an atlas or your textbook to determine the climate and vegetation of these same regions.

  Regions of High Erosion                     Climate                              Natural Vegetation

GREAT PLAINS                       semiarid                              grassland

ANDES MOUNTAINS              highland                              forest

SOUTHEAST ASIA                  tropical wet                         rainforest

SOUTH ASIA                            tropical monsoonal           savanna

 

  Regions of Low Erosion                      Climate                              Natural Vegetation

EASTERN USA                        humid temperate               forest

ARCTIC                                     frozen                                  tundra

SAHARA                                   hyperarid                            desert

AUSTRALIA                              hyperarid                            desert

 

6.   a.   Do the regions of highest and lowest erosion rates listed for Question 5 have the types of climates and biomes you listed as answers to Question 4?  If not, which ones do not match? REASONABLY WELL, IF ONE CONSIDERS BIOME/VEGETATION TYPES AND ALSO MOUNTAINOUS TERRAIN!

 

b.   If the regions of high and low erosion you listed in Question 5 do not have the types of climates and biomes you listed in Question 4, explain what other factors might be contributing to high or low rates of erosion in these areas.

VEGETATION COVER IS A CRITICAL FACTOR, BUT ALSO TOPOGRAPHIC RELIEF, PERMAFROST, COASTS

 

Figure 19.10  World Distribution of Erosion

Adobe Systems
 

 

 

 

 



Name:  _______________________________________________ Section:_______________________

part 3:  storm hydrographs

1.   The response of two drainage basins to a storm event is presented in Table 19.3.  These drainage basins are the same size and have similar characteristics; the only difference between these two drainage basins is the fact that one is in rural land use and the other is in urban land use.  Plot the data in Table 19.3 on graph paper to create a hydrograph for each drainage basin.  The two hydrographs should be on the same graph, and they should begin at the same point in time.  Label the axes clearly and label the hydrograph lines clearly. 

TABLE 19.3  Stream flow Data for Two Drainage Basins from Identical Storm Events

   Rural Drainage Basin                  Urban Drainage Basin

      Time       Discharge                 Time        Discharge

      (hours)          (cfs)                  (hours)          (cfs)

         1.0              1.5                       1.0              0.5

         2.0              1.7                       2.0              0.8

         3.0              1.5                       3.0              0.5

         4.0              5.0                       4.0              9.0

         5.0            15.0                       5.0            36.0

         6.0            20.0                       6.0            51.0

         7.0            26.0                       7.0            40.0

         8.0            22.0                       8.0            29.0

         9.0            18.0                       9.0            16.0

       10.0            14.0                     10.0              9.0

       11.0            11.0                     11.0              5.0

       12.0              8.0                     12.0              3.0

       13.0              5.0                     13.0              2.0

       14.0              1.7                     14.0              1.5

       15.0              1.5                     15.0              0.5

       16.0              1.5                     16.0              0.8

2.   What is the peak discharge for:

a.   the urban basin?     51 CFS                  b.   the rural basin?         26 CFS

3.   Since both basins experienced identical storm events, why is the peak discharge for one basin higher than for the other basin? THE URBAN BASIN PROBABLY "USES" LESS WATER FOR INTERCEPTION (ASSUMING THERE IS LESS VEGETATION) AND ALSO LESS FOR INFILTRATION (ASSUMING A HIGH PROPORTION OF THE URBAN LAND SURFACE HAS PAVEMENT, ROOFTOPS, OR OTHER IMPERMEABLE MATERIALS COVERING IT). RURAL VEGETATION AND SOIL HOLD THE EXTRA WATER LONGER AND MORE GRADUALLY  RELEASE IT.  THE URBAN BASIN PUTS NEARLY ALL THE WATER MORE IMMEDIATELY INTO THE RIVERS AND STREAMS AS RUNOFF.

4.   a.   Which drainage basin experiences its peak discharge earlier?              THE URBAN

b.   How many hours later does the flow from the other drainage basin peak? ONE HOUR

c.   Why does one hydrograph peak later than the other hydrograph? WITH LESS VEGETATION AND MORE PAVEMENT, THE URBAN BASIN HAS NEARLY ALL THE WATER GO MORE IMMEDIATELY INTO THE RIVERS AND STREAMS AS RUNOFF.

5.   If planners wanted to increase the amount of urban area in a drainage basin, they could expect river flow conditions to change from those shown on your graph for the rural basin to those shown on your graph for the urban basin.  What would be the implications of this change in the in stream flow patterns on the land directly adjacent to a stream? MORE FLASH-FLOODING, AND HIGHER FLOOD STAGES.  THIS IS EXACTLY WHAT HAS HAPPENED IN MANY URBAN AREAS ("STORM WATER FLOODING"), SUCH AS IN WASHINGTON D.C.