Section 5-Runoff Management Flashcards
Runoff Management Planning looks at ____ and____ flow patterns, _______, ______ and ________.
pre and post flow patterns. Diversions, retaining, detaining
Runoff management typical storm design is
24 hr/10 yr
Types of runoff management include (3 itmes)
diversions, waterways, and conduits
Types of energy/ velocity dissipation include (5 items)
check dams, level spreaders, rock culvert outlets, grade stabilization structures
Two components to predict energy/velocity
runoff volume, peak rate of discharge
Hydrologic Cycle
waters of the earth; rainfall, percolation, runoff, storage, evaporation
Hydrograph
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.
Runoff volume
area under hydrograph is the runoff volume
runoff volume is dependant upon (3 itmes)
soils, size of drainage area, type and density of ground cover
Q=
runoff in inches multiplied by the watershed area
Factors affecting runoff (7 items)
- precipitation- amount and intensity
- time parameters
- watershed areas
- ground cover
- antecedent moisture condition
- storage in the watershed
- soil permeability
Precipitation (P)-
isohyetal maps as source, provides 2-100 year, 24 hour storm durations
Time of Concentration (Tc)
time it takes runoff to travel from most distant point to the outfall (design point).
Time of Concentration-Higher peak volumes and velocities have significant impacts on stormwater management. T/F
T
TOC Travel time-
time it takes runoff to travel from one location to another within the watershed.
TOC sheet flow-
flow over upland area where there is no defined water course or channel. Flows are generally less than 1/10’.
sheet flow typically represents a small portion of Tc. T/F
F - Typically represent a significant portion of Tc .
TOC-Shallow concentrated flow
occurs once flow begins to form rills
Shallow concentrated flow usally happens within _____ feet of onset of runoff, rarely after _____ feet.
150’, 300’
Channel Flow-when visible from (3 items)
aerial photos, blue lines exist on USGS quad sheets, or can be verified in the field.
Manning’s is used to predict _______ for flow.
velocity
losses that occur before runoff begins include (3 items)
interception, evaporation, and infiltration
Soil permeability-
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.
Soil permeability Group A
deep, well to excessively drained sands or gravels with high rate of water transmission, greater than 0.30 in/hr.
Soil permeability Group B
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.
Soil permeability Group C
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.
Soil permeability Group D
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.
Urbanization may alter the soil to the point where it no longer acts as its original designation. T/F
T
Three development stages of planning for runoff management ( 3 phases)
- pre developed
- during grading/construction
- developed
Internal site condition planning (3 items)
- divert and direct sediment laden water to BMPs
- use existing or new controls ASAP
- design temporary controls
Site perimeter planning (3 items)
- manage run on
- manage runoff
- protect internal active inlets
Best ________ and _______control will not be effective without proper runoff management
erosion, sediment
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 ________.
Soil loss
Sheet and rill
Slope
Management system
Rusle estates sediment yield. T/F
F- musle determines sediment yield
Unit of measurement for volume of runoff in a storm event for musle equation
Acre feet. Inches of runoff 1/12number of acres
Q=
Peak flow for a storm event in Cfs
