Section 5-Runoff Management

Question 1

Runoff Management Planning looks at ____ and____ flow patterns, _______, ______ and ________.

Answer 1

pre and post flow patterns. Diversions, retaining, detaining

Question 2

Runoff management typical storm design is

Answer 2

24 hr/10 yr

Question 3

Types of runoff management include (3 itmes)

Answer 3

diversions, waterways, and conduits

Question 4

Types of energy/ velocity dissipation include (5 items)

Answer 4

check dams, level spreaders, rock culvert outlets, grade stabilization structures

Question 5

Two components to predict energy/velocity

Answer 5

runoff volume, peak rate of discharge

Question 6

Hydrologic Cycle

Answer 6

waters of the earth; rainfall, percolation, runoff, storage, evaporation

Question 7

Hydrograph

Answer 7

graphical expression of surface runoff from a specific storm event in a watershed to a given design point with respect to time. Peak and shape depend upon geometrical nature of watershed. Long, narrow, steep=peak quickly, short duration. Wide, flat=delayed peak, longer duration.

Question 8

Runoff volume

Answer 8

area under hydrograph is the runoff volume

Question 9

runoff volume is dependant upon (3 itmes)

Answer 9

soils, size of drainage area, type and density of ground cover

Question 10

Q=

Answer 10

runoff in inches multiplied by the watershed area

Question 11

Factors affecting runoff (7 items)

Answer 11

1. precipitation- amount and intensity
2. time parameters
3. watershed areas
4. ground cover
5. antecedent moisture condition
6. storage in the watershed
7. soil permeability

Question 12

Precipitation (P)-

Answer 12

isohyetal maps as source, provides 2-100 year, 24 hour storm durations

Question 13

Time of Concentration (Tc)

Answer 13

time it takes runoff to travel from most distant point to the outfall (design point).

Question 14

Time of Concentration-Higher peak volumes and velocities have significant impacts on stormwater management. T/F

Answer 14

T

Question 15

TOC Travel time-

Answer 15

time it takes runoff to travel from one location to another within the watershed.

Question 16

TOC sheet flow-

Answer 16

flow over upland area where there is no defined water course or channel. Flows are generally less than 1/10’.

Question 17

sheet flow typically represents a small portion of Tc. T/F

Answer 17

F - Typically represent a significant portion of Tc .

Question 18

TOC-Shallow concentrated flow

Answer 18

occurs once flow begins to form rills

Question 19

Shallow concentrated flow usally happens within _____ feet of onset of runoff, rarely after _____ feet.

Answer 19

150’, 300’

Question 20

Channel Flow-when visible from (3 items)

Answer 20

aerial photos, blue lines exist on USGS quad sheets, or can be verified in the field.

Question 21

Manning’s is used to predict _______ for flow.

Answer 21

velocity

Question 22

losses that occur before runoff begins include (3 items)

Answer 22

interception, evaporation, and infiltration

Question 23

Soil permeability-

Answer 23

rate of infiltration obtained for bare soil after prolonged wetting, 4 soil groups (Hydrologic Soil Group A,B,C,D). rate at which water enters the soil at the soil surface. One element used in determinig runoff curve numbers. Rate at which water moves within the soil (transmission rate). Provided in a table.

Question 24

Soil permeability Group A

Answer 24

deep, well to excessively drained sands or gravels with high rate of water transmission, greater than 0.30 in/hr.

Question 25

Soil permeability Group B

Answer 25

moderately deep to deep, moderately well to well drained solid with moderately fine to moderately coarse textures. Moderate rate water transmission, 0.15-0.30 in/hr.

Question 26

Soil permeability Group C

Answer 26

low infiltration rate, consist chiefly of soils with a layer that impedes downward movement of water, moderately fine to fine texture, low rate of water transmission 0.05-0.15 in/hr.

Question 27

Soil permeability Group D

Answer 27

high runoff potential. Very low infiltration, consist chiefly of clay soils with high shrink/swell potential, soils with high permanent water table, with claypan, clay layer near the surface, or shallow soils over nearly impervious material. Very low rate of water transmission 0-0.15 in/hr.

Question 28

Urbanization may alter the soil to the point where it no longer acts as its original designation. T/F

Answer 28

T

Question 29

Three development stages of planning for runoff management ( 3 phases)

Answer 29

1. pre developed
2. during grading/construction
3. developed

Question 30

Internal site condition planning (3 items)

Answer 30

1. divert and direct sediment laden water to BMPs
2. use existing or new controls ASAP
3. design temporary controls

Question 31

Site perimeter planning (3 items)

Answer 31

1. manage run on
2. manage runoff
3. protect internal active inlets

Question 32

Best ________ and _______control will not be effective without proper runoff management

Answer 32

erosion, sediment

Question 33

Rusle is a soil loss equation that predicts average annual ________ from what types of erosion? It is carried from a specific ______ that has a specified _______ and ________.

Answer 33

Soil loss
Sheet and rill
Slope
Management system

Question 34

Rusle estates sediment yield. T/F

Answer 34

F- musle determines sediment yield

Question 35

Unit of measurement for volume of runoff in a storm event for musle equation

Answer 35

Acre feet. Inches of runoff 1/12number of acres

Question 36

Q=

Answer 36

Peak flow for a storm event in Cfs