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LARE SECTION 4 > Greater Detail: GRADING and STORMWATER > Flashcards

Greater Detail: GRADING and STORMWATER Flashcards

1
Q

Line type used for existing contours

A

dashed

interval labeled on uphill side

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2
Q

Line type used for proposed contours

A

solid

interval labeled on uphill side

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3
Q

FFE
TW/BW
TC/BC
TS/BS

A

Finished floor elevation
Top of Wall / Bottom of Wall
Top of Curb / Bottom of Curb
Top of Stair / Bottom of Stair

*all will include a spot elevation

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4
Q

BF
HP/LP
TF or RE
INV. EL

A

Bottom of Footing
High Point / Low Point
Top of Frame or Rim Elevation
Invert Elevation

*all will include a spot elevation

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5
Q

CB
DI
MH
AD

A

Catch Basin
Drain Inlet
Manhole
Area Drain

*all will include top of frame and invert elevation (except for area drains, which only requires top of frame)

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6
Q 
CIP
RCP
CMP
VCP
PVC
A 
Cast Iron Pipe
Reinforced Concrete Pipe
Corrugated Metal Pipe
Vitrified Clay Pipe
Polyvinyl Chloride Pipe

*all will include a pipe size

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7
Q

PL
CLL
CL

A

Property Line ____ __ __ ____
Contract Limit Line ____ __ ____
Center Line ____ _ ____

  • center lines will include a flow direction
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8
Q

CF to CY

A

divide by 27

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9
Q

SF to SY

A

divide by 9

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10
Q

Cut / fill calc. that is best for linear construction (roads, pathways, utility trenching)

METHOD:
Take cross sections at a certain interval, calculate areas of cut and fill for each section, average the areas of all sections taken and multiply that area by the length

A

Average End Area

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11
Q

Cut / fill calc. that is best for large but relatively simple grading plans
May be used to calculate volumes of water in a pond / lake

Establish no cut / no fill line, measure SF area of cut and fill for each contour within the no cut / no fill line, calc. total cut and fill, multiply by the contour interval

A

Contour Area Method

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12
Q

Cut / fill calc. that is best for complex grading projects and urban conditions

Overlay a grid over the area to be regraded, calculate the average change in cut / fill per cell by determining the average difference in elevation of all 4 corners, add average cut and fill together and multiply by the area of one grid cell

A

Borrow Pit Method (aka Grid Method)

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13
Q

The final grade after all landscape development has been completed; top surface of planted areas, pavements, etc. Normally designated by contours and spot elevations on a grading plan

A

Finished Grade

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14
Q

Top of the material on which the surface material (topsoil, pavement + base layers, etc) is placed. Subgrade is represented by the top of a fill situation and the bottom of a cut excavation.

A

Subgrade

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15
Q

Subgrade that must attain a specified density

A

Compacted Subgrade

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16
Q

Indicates a soil that has not been excavated or changed in any way

A

Undisturbed Subgrade

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17
Q

Imported material placed beneath pavements (usually course or fine aggregate)

A

Base / Subbase

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18
Q

Usually the elevation of the first floor of a structure; may also be used to designate the elevation of any floor

A

Finished Floor Elevation

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19
Q

The process of removing soil

Proposed contours extend across existing contours in the UPHILL direction

A

Cut / Cutting

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20
Q

The process of adding soil

Proposed contours extend across existing contours in the DOWNHILL direction

A

Fill / Filling

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21
Q

Fill material that is imported to the site

A

Borrow

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22
Q

The densification of soil under controlled conditions, particularly a specified moisture content

A

Compaction

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23
Q

Normally the top layer of a soil profile; may range in thickness from 1” - 1’-0” or greater.

Has a high organic content and is therefore subject to decomposition and is not an appropriate subgrade material for structures

A

Topsoil

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24
Q

Problem soils / conditions as it relates to construction (6)

A
  1. Loose silts
  2. Soft clay
  3. Fine water-bearing sands
  4. Soils with high organic content (e.g. peat)
  5. High water table
  6. Bedrock
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25
Q

When soils become unconsolidated due to excavation, scraping, removal of vegetation etc

A

Erosion

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26
Q

Most effective strategy for minimizing erosion

A

Reduce area to be disturbed

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27
Q

TESC Plans

A

Temporary Erosion and Sedimentation Control Plans

Soil erosion and sedimentation control plans may be required by code to be submitted prior to start of construction

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28
Q

Methods of erosion control (2)

A
  1. Strip and stockpile existing topsoil to avoid unnecessary loss (to be replaced after regrading is complete)
  2. Grading should be informed by the erosion tendency of the site’s soil (increasing length and degree of slope will increase erosion potential)
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29
Q

If balance of cut and fill cannot be met is it better to have more cut or more fill

A

CUT

  • less costly to export soil than to purchase and import soil
  • cut subgrade / finished grade is more stable and erosion resistant than filled subgrade / finished grade
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30
Q

RIDGES (and roadway crowns) Point ___

Contour signature

A

Downhill

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31
Q

VALLEYS (and swales) Point ___

Contour signature

A

Uphill

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32
Q

Concave line spacing ___

Contour signature

A

Increasing distance in the downhill direction

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33
Q

Convex line spacing ___

Contour signature

A

Increasing distance in the uphill direction

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34
Q

Most expensive method of accommodating grade change:

A

Retaining wall

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35
Q

Max slope of mowed lawn

A

3:1 (33.33%)

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36
Q

Max slope of planted area

A

2:1 (50%)

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37
Q

Min slope to be visually significant

A

5:1 (20%)

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38
Q

Purpose of a crown in roadway design (2)

A
  1. Positive Drainage

2. Visually separate opposing traffic lanes

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39
Q

Parabolic Crown Section (roadways)

A

Rounded crown; common for asphalt; contours are rounded

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40
Q

Tangential Crown Section (roadways)

A

Pointed crown; common for concrete; contours are V shaped

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41
Q

Reverse Crown (roadways)

A

Typically used where it is not desirable to direct stormwater runoff to the edge of the road or in restricted road conditions (e.g. urban alleyway)

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42
Q

Curb Heights

A

6” typically

min 2”, max 8”

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43
Q

A relative high point

Example:
A high point in a swale that is higher in the longitudinal direction but lower in the perpendicular direction / than the edge if swale

A

Saddle

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44
Q

3 reasons to pitch water away from buildings

A
  1. Water penetration potential
  2. Reduce bearing capacity of soils
  3. Moisture on building materials
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45
Q

Delineates the limit of grading work

A

Limit line

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46
Q

Grading Plan Elements (4)

A
  • All existing and proposed features
  • Proposed contours are solid
  • Existing contours are dashed
  • Spot elevations (corners of features, top and bottom of vertical elements, FFEs, HP and LP, top of frame / rim, inverts
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47
Q

Notes on a grading plan (4)

A
  • General / explanatory info
  • Description of unique conditions
  • Source of existing condition info
  • Benchmarks and reference datum
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48
Q

Max. proposed slope depends on:

A
  • shear strength of exposed soil
  • maintenance considerations
  • stabilization techniques
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49
Q

Grading sequence in construction (4)

A
  1. Site preparation
  2. Bulk excavation
  3. Backfilling and fine grading
  4. Finish surfacing
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50
Q

The time needed for water to flow from the most remote point in a watershed to the watershed outlet. It is a function of the topography, geology, and land use within the watershed.

A

Time of Concentration

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51
Q

Construction or natural drainage channel used to direct surface flow

Parabolic, trapezoidal, or triangular cross sections

Used to divert water away from an object in the landscape in order to protect it from flooding or to keep the subsoil under a structure dry.

A

Swale

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52
Q

Structure that allows water course to flow beneath o road, walk, or highway

A

Culvert

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53
Q

Conc. structure 2.5-4ft dia used to collect and divert surface runoff to an underground conduction system. Includes a sump or sediment bowl at base to trap debris

A

Catch Basin

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54
Q

1 catch basin per ____ paved area (typically)

A

10,000 SF

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55
Q

Structure that directs water directly into a drain pipe (does not have a sump)

A

Drain Inlet

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56
Q

Prefabricated structure that collects runoff from paved areas. May include a sediment bucket.

A

Area Drain

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57
Q

1 area drain per ____ paved area (typically)

A

1,000 - 2,000 SF

58
Q

Linear Inlet structure used to collect sheet flow runoff in paved areas

A

Trench Drain

59
Q

Structure usually 4FT dia made of conc., brick, or fiberglass rings that allows a person to enter a space below ground.

Used where there is a change in the size, slope, or direction of underground pipes

Round or rectangular

Often combined with a catch basin

A

Manhole

60
Q

Limitations to infiltration facilities (3)

A

Soil permeability rates

Potential reduction of permeability over time

Potential for groundwater contamination

61
Q

Conditions to be studied for any infiltration facility (6)

A

Depth to groundwater

Seasonal variation in groundwater level

Slope and direction of groundwater flow

Soil permeability

Vegetative cover

Quality of runoff

62
Q

q = CIA

A

The Rational Method

Used to compute peak rate of runoff for a SMALL drainage area (e.g. less than 100 acres); measured in cubic feet per second. Used for the design of a range of drainage structures (length of sewer, inlets, detention ponds, etc)

C = runoff coefficient (0-1); depends on land use, soils, and slope.

I = rainfall intensity in in/hr for the design storm frequency (e.g. 10-year storm) and for the time of concentration of the drainage area

A = area of drainage area (acres)

63
Q

C = 0

q = CIA

A

Completely pervious surface

64
Q

C = 1

q = CIA

A

Completely impervious surface

65
Q

Design Storm

A

A storm with a frequency and duration for which a management system is designed.

66
Q

Nomograph

A

Used to estimate time of concentration / overland flow time

Take 2 given values and locate them on the nomograph; draw a straight line between them to solve for other values

67
Q

Modified Rational Method

A

Accounts for a ‘antecedent precipitation’ factor (q = CCaIA)

Where Ca = multiplier for storm event (e.g. 2-10 yr = 1.0; 25 yr = 1.1; 50 yr = 1.2, 100 yr = 1.25)

Accounts for the fact that in this more infrequent major storm events that the soil will already be saturated / have a substantially reduced capacity to infiltrate

68
Q

Used for the design of storage ponds and reservoirs (inflow and outflow volumes)
Plot of flow rate (q) over time (T)

A graph showing, for a given point on a channel, the discharge, stage, velocity, or other property of water with respect to time

A

Hydrograph

69
Q

Open Drainage Systems

  • define
  • provide example
  • biggest concerns
A

All surface runoff is collected and conveyed on the open ground

E.g. swales, gutters, channels, culverts, detention, retention, sediment basin, infiltration basins

Erosion and sediment are biggest concerns

70
Q

Closed Drainage Systems

  • define
  • provide example
  • advantages
  • disadvantages
A

All surface runoff is collected at surface inlets and conveyed by underground pipes to an outlet

E.g. catch basins, drain inlets, area drains, trench drains, manholes, piping

Advantage: runoff may be intercepted before volume and velocity contribute to erosion

Disadvantages: costly, sediment is not filtered out (inherently), erosion may still occur at discharge points, reduced opportunity for infiltration

71
Q

Combination System

  • define
  • advantages
A

Combines open and closed drainage systems

Advantages: reduced costs, lower potential for soil erosion bc surface runoff volumes are reduced, lower potential for erosion at discharge point bc volume is reduced

72
Q

(3) considerations for pipe design

A
  1. pipes should increase in size toward outlet
  2. typically straight (less clogging, easier to clean)
  3. must pitch; pitch should flow with surface slope +/- to reduce excavation
73
Q

Velocity of water in a swale is modified by (2)

A
  1. slope of swale
  2. vegetation (type and condition, particularly length)

Where excessive velocity cannot be avoided structural linings should be used (rip rap, gabion, concrete)

74
Q

Min parameters of a swale design

A

Peak flow for a 10-year storm

75
Q

2 equations used to determine dimensions of open channels (e.g. swales)

A

Manning’s Equation

Continuity Equation

76
Q

A formula for calculating the velocity of flow in a channel as a function of relative roughness, cross-sectional configuration, and gradient

A

Manning’s Equation

77
Q

A formula expressing the principle of conservation of mass as applied to the flow of water. It states that the product of cross-section of flow and velocity at any point in a channel is a constant

A

Continuity Equation

78
Q

The velocity at which unstable flow conditions begin to occur

A

Critical Velocity

79
Q

First step in designing any drainage system

A

Determine availability of an adequate outlet

80
Q

Pipe design: min depth

A

3FT

Minimizes damage from traffic and frost

81
Q

Pipe design: constraint when locating collection points

A

Locate away from trees, main walks, buildings as occasional clogging may cause flooding

82
Q

Pipe design: what is needed where pipes join

A

Manhole, catch basin, or junction box

83
Q

Pipe design: size may be determined by

A

Manning’s Equation and Continuity Equation

84
Q

Principle of Subsurface Drainage and methods

A

Excess water removed by gravity; capillary action / surface tension retains enough water to support plants

Methods: 
Clay tile (segmented)

Perforated porous pipe (holes placed downward)

85
Q

What is the min. depth of a swale

A

6”

source: LARE app

86
Q

What is an acceptable range for longitudinal swale slope

A

2-4%

source: LARE app

87
Q

Min. amount of slope allowable on a playing field

A
  1. 5%

source: LARE app

88
Q

An accessible route with a running (longitudinal) slope GREATER THAN ___ is a ramp

A

1:20

Or 5%

89
Q

Purpose of cross slope:

A

To create positive drainage

90
Q

GRADING SEQUENCE 2:

Rough grading phase; major earthmoving and shaping for major earth forms and providing footing / foundation excavation for all structures

A

Bulk Excavation

91
Q

GRADING SEQUENCE 3:

Undertaken after all structures have been built

Backfill must be compacted to minimize future settlement (compaction should not damage new / existing subgrade structures)

Fine grading ensures that forms and surfaces meet the desired grades

A

Backfilling and Fine Grading

92
Q

GRADING SEQUENCE 4:

Paved / hard surfaces first, then topsoil is placed (salvaged or new)

Subsoil is typically roughened / scarified to allow topsoil to bond better and to promote root growth between soil layers

Elevations of topsoil and final surfaces must meet the elevations of the grading plan

A

Finish Surfacing

93
Q

Uptake and release from trees, plants and the ground

A

Evapotranspiration and Bioretention

94
Q

Best plant for bioretention

A

Broadleaf evergreens (evergreens transpire year-round; broadleaved biomass > needled evergreen)

95
Q

The temporary capture and slow release of water to stormwater systems / infrastructure

A

Detention

96
Q

The slowing down of stormwater to permit it to soak into soils and ultimately groundwater systems; water table height and soil type are critical

A

Infiltration

97
Q

Stormwater Management System Functions (6)

A
  1. Evapotranspiration and Bioretention
  2. Evaporation
  3. Detention
  4. Infiltration
  5. Capture
  6. Treatment
98
Q

The process of settling out particulate matter from runoff; when water is slowed down, sediment is allowed to sink

A

Sedimentation Management

99
Q

Occurs as runoff flows through plant material and soil; sediment is physically strained out of runoff; sandy soils are ideal
Other benefits of runoff carried through plant material: plant resistance (slows water velocity)

A

Filtration

100
Q

Runoff from impervious surfaces picks up added heat

A

Thermal Attenuation

101
Q

The process of removing soluble nutrients, metals, and organics by binding ions and molecules to other particles or organic matter or clay

A

Adsorption

102
Q

Benefits of Infiltration Systems

1 Primary, 4 Secondary

A

Primary:
1. Reduce surface runoff while recharging groundwater

Secondary:
1. Reduce downstream peak flows

  1. Reduce subsidence related to groundwater depletion
  2. Preserve existing vegetation
  3. Lowers development costs
103
Q

Limitations of Infiltration Systems (4)

A
  1. Soil permeability rates
  2. Potential reduction of permeability rates over time
  3. Potential for groundwater contamination
  4. Infiltration systems improve water quality but should not be used to remove sediment / other particulate matter; any infiltration system must include filter strips or sediment traps before it enters the infiltration device
104
Q

Temporarily stores runoff for a certain design storm or specific volume and allows water to infiltrate (e.g. rain garden)

May be a combined infiltration + detention system

Drawbacks: may require a large area; not adaptable to multiple uses (e.g. recreation); high rate of failure due to improper maintenance and / or installation

A

Infiltration Basins

105
Q

An excavation backfilled w/ coarse aggregate stone
Voids bw stone provide volume for temporary water storage

Surface of facility may be planted w/ inlets or is highly porous: sand, stone, gravel

Best for relatively small drainage areas

Observation wells should be installed vertically in the facility to periodically monitor change in infiltration rate

A

Infiltration Trenches

106
Q

Similar to infiltration trench but storage is oriented vertically (into the ground) rather than laterally

Variation w.o stone: prefabricated structures that can carry heavier loads and do not need stone backfill = greater volume of water stored in smaller footprint

A

Dry Well

107
Q

Suitable for low-volume roads and where subgrade soil conditions provide sufficient permeability, depth to groundwater and where contamination will not occur from degraded stormwater quality

A

Porous Pavement

108
Q

Structured or landform impoundments constructed to collect runoff for the purpose of reducing peak flow and controlling the rate of flow

A

Detention Systems

109
Q

Basins w/ a permanent pool of water

Benefits: increased property values (when well designed), recreational opportunities, habitat creation

Disadvantages: safety problems, algal blooms, odors, mosquitoes, need for maintenance (e.g. sediment removal)

A

Retention Basin

110
Q

Dry pond / dry basin

Control peak discharge rates through temporary storage of storm runoff where outflow rates are set at or below pre-development rates

Does not enhance stormwater quality (

May be doubled w/ recreation use but must include low-flow channels to provide positive drainage toward outlet and / or subsurface drainage (min 2% toward outlet)

Elongated forms preferable : elegonates flow from inlet to outlet

Side slopes of basin should not exceed 3:1

Maintenance access way min 10ft wide with max slope of 5:1 should be provided

A

Detention Basin

111
Q

May be included as part of a detention / retention basin design

Provides additional volume for settling of sediment (retention-type)

Outlet orifice is small, which slows outward flow and provides more time for contaminants to settle out (detention-type)

A

Water Quality Basin

112
Q

An impoundment area / structure that slows the velocity of runoff in order to allow sediment particles to settle out

A

Sediment Basin

113
Q

Pipe and control structure are sized to slow stormwater release to a specified rate

Must include an overflow bypass should the pipe fill up

A

Detention Pipes and Vaults

114
Q

Drainage of water from the roof is slowed by flow control device

Requires additional waterproofing membranes, scuppers, or overflew drains to control a max. depth of water ponding on the roof (typically limited to 4” max)

Structural engineers should be consulted to ensure that the roof can support additional loading of water

A

Rooftop Detention / Blueroof

115
Q

All surface runoff is collected and conveyed on the open ground

E.g. swales, gutters, channels, culverts, detention, retention, sediment basin, infiltration basins

A

Open Drainage System

Considerations:

  1. Volume and velocity of runoff (prevent erosion; If necessary, flow energy should be dissipated)
  2. Collecting sediment at discharge points
116
Q

All surface runoff is collected at surface inlets and conveyed by underground pipes to an outlet

E.g. catch basins, drain inlets, area drains, trench drains, manholes, piping

A

Closed Drainage System

117
Q

Closed Drainage Sys. Advantages (1) / Disadvantages (4):

A

Advantage:
1. Runoff may be intercepted before volume and velocity contribute to erosion

Disadvantages:

  1. Costly
  2. Sediment is not filtered out (inherently)
  3. Erosion may still occur at discharge points
  4. Reduced opportunity for infiltration
118
Q

(3) Basic Functions of any storm drainage system:

A
  1. Collect
  2. Conduct
  3. Dispose
119
Q

Major concerns of swale design (2)

A

Erosion and sedimentation

120
Q

An area bounded by ridges having a single outlet from which water can flow

A

Watershed

121
Q

Spot elevations on hardscape should be calculated to within

A

0.01 ft

122
Q

Spot elevations on softscape should be calculated to within

A

0.1 ft

123
Q

In open landscapes, slopes of less than __% appear flat to the human eye

A

2%

124
Q

Absolute min % for draining water across a very smooth, ridgid material (e.g. storm drain pipes, conc. gutters, conc. slabs).
Not recommended unless its impossible to avoid or you are given explicit permission to do so in the problem statement

A

0.5%

125
Q

A workable minimum for shedding surface water across paving materials.
Ok for a cross slope.

A

1%

126
Q

The generally recommended gradient for most any surface. Moves water well on most surfaces.
Recommended as the cross slope on sidewalks and the crown cross slope on roads.
Maximum allowable cross slope under ADA guidelines

A

2%

127
Q

Gradient at which slope becomes obvious to the human eye

Usually the maximum gradient accepted for road intersections.

A

3%

128
Q

Maximum longitudinal slope allowed for accessible ramps, including curb ramps

A
  1. 33%

12: 1

129
Q

Rational Method Runoff Coefficient LOW values denote

A

Less runoff

130
Q

Rational Method Runoff Coefficient HIGH values denote

A

More runoff

131
Q

How many SF in an acre

A

43,560 SF

132
Q

Lowest elevation inside a pipe; essentially the flow line of water

A

INVERT

133
Q

Solve for invert

A

= Finished grade - required cover over pipe - pipe diameter

on LARE you can assume pipe thickness is zero, unless otherwise specified

134
Q

Occurs whenever the water level immediately downstream of a pipe outlet rises above the top of the pipe.

A

Surcharge

135
Q

Soil depth from finished grade to top of pipe

A

Cover

136
Q

Min cover to maintain over pipes for LARE (unless otherwise specified)

A

12 inches

137
Q

To reduce clogging, pipe sizes should

A

Never be reduced in a downstream direction

138
Q

Spot elevations on hardscape should be calculated to within

A

0.01ft

unless otherwise indicated

139
Q

Spot elevations on softscape should be calculated to within

A

0.1ft

unless otherwise indicated

140
Q

As a general rule, keep the FFE of a building __ inches above adjacent grade

A

6 inches

141
Q

Max swale side slope

unless otherwise stated

A

3:1 ( 33.3%)

142
Q

Ideal swale longitudinal slope

unless otherwise stated

A

2%

LARE SECTION 4 (7 decks)

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