Lecture 8 - Stormwater Management Structures

Question 1

What approach has historical stormwater management design relied on?

Answer 1

drainage efficiency approach

Question 2

What is the impact of urban stormwater?

Answer 2

fundamental alteration of the hydrologic cycle

Question 3

What are the hydrologic watershed impacts of urban stormwater?

Answer 3

increased peak flows, reduced infiltration, reduced groundwater recharge, lower baseflows

Question 4

What are the physical watershed impacts of urban stormwater?

Answer 4

channel alteration, sedimentation, disruptions to benthic habitat, elevated water temperatures

Question 5

What are the water quality watershed impacts of urban stormwater?

Answer 5

pathogens, nutrients, inorganics (metals, salt), toxic organics

Question 6

What do the watershed impact factors influence?

Answer 6

the structure and function of ecosystem components

Question 7

What are ecological maintenance flows (EMFs)?

Answer 7

streamflow required to maintain acquatic habitat

Question 8

What are the percentages associated with Ecological Maintenance Flows (EMFs) in the Atlantic Provinces?

Answer 8

25% of mean annual flow and 75% of median monthly flow

Question 9

What other indices can be used to define EMFs?

Answer 9

Flow durations indices (Q90, Q95), 7 day average minimum flows that occur on average every x amount of years (7Q2, 7Q10, 7Q20), aqautic baseflow method (ABF)

Question 10

What is the acquatic baseflow method? (ABF)

Answer 10

0.005 m3/(s-km2) used by USFWS for small ungauged basins in New England

Question 11

Describe the relevant characteristics of the Kuhn Marsh Watershed.

Answer 11

28 ha urban catchment draining residential area, 27% impermeable surfaces, stormwater dishcharged to 2.2 ha wetland

Question 12

Describe the study of the Kuhn Marsh Watershed.

Answer 12

16 month study, baseflow and stormflow loading of nutrients, bacteria, metals, organic carbon, assessment of wetland fuction

Question 13

What were the water quality issues with the Kuhn Marsh watershed?

Answer 13

nutrient loading, elevated E. coli, heavy metals

Question 14

give a general overview of stormwater management objectives

Answer 14

first step is to identify the design objectives for stormwater management, most jurisdictions will specify the objectives that the stormwater management systems must meet

Question 15

Describe the peak flow management objective.

Answer 15

prevent flooding, damage to downstream infrastructure, channel erosion, most guidelines specify that post-development flows must be less than pre-development flows

Question 16

Descirbe the water quantity management objective.

Answer 16

systems are designed to manage a specific volume of stormwater, reduces peak flows, provides water quality treatment and possibly allows for infiltration

Question 17

Describe the water quality management objective.

Answer 17

systems are designed to remove a specific amount of contaminant load (typically sediments), could be a specified water quality metric (system must remove 50% of suspended sediment), could be specified as a design-based goal (systems must retain stormwater for at least 24 hr)

Question 18

What are the two general types of stormwater control approaches?

Answer 18

lot level controls (source control), end of pipe controls

Question 19

What are the two different types of approaches for lot level control.

Answer 19

temporary storage and infiltration and long-term storage and reuse

Question 19

What are two common methods of temporary storage?

Answer 19

parking lot storage, rooftop storage

Question 20

What size watershed is lot level control appropriate for?

Answer 20

less than 2 ha

Question 21

What are the infiltration/long-term storage methods for lot level control?

Answer 21

dry wells, cisterns, infiltration trenches, infiltration swales, rain gardens, pervious pavements

Question 22

What is the main goal of long-term storage for most systems?

Answer 22

to retain water volumes from a small area and allow it to infiltrate

Question 23

What are some considerations/challenges for lot level infiltration systems?

Answer 23

restrictive soils and geology, climate (ice, snow, frozen soils), maintenance, groundwater contamination, liability for flooding issues/

Question 24

What are some end-of-pipe control strategies?

Answer 24

detention and retention ponds, constructed wetlands, infiltration basins, engineered filtration systems

Question 25

What are detention ponds used for?

Answer 25

to dampen peak flow rates

Question 26

What are retention ponds?

Answer 26

surface water treatment systems that are designed to retain stormwater for greater than 18 hours, typically designed to retain runoff from a moderate rainfall event (2 yr, 24 hr storm), much larger than detention ponds

Question 27

Give some more information about retention and detention ponds.

Answer 27

most widely applied stormwater management technology, can be either wet or dry ponds, also called infiltration basin

Question 28

What are constructed wetlands?

Answer 28

same basic design principles as retention ponds, but designed to allow for emergent aquatic vegetation establishment

Question 29

Why do constructed wetlands need to be quite large?

Answer 29

water depths need to be less than 1 m to allow for vegetation establishment, so needs to be large to achieve required retention times for treatment

Question 30

What are the limitations of the load reduction approach?

Answer 30

does not restore/retain natural hydrologic pathways, poor removal of dissolved contaminant load, long term performance

Question 31

What is the length to width ratio for detention/retention ponds?

Answer 31

greater than 3:1

Question 32

What do wet ponds have? How deep is this?

Answer 32

permanent pools, typically 1-2 m

Question 33

What can retention/detention ponds be designed as?

Answer 33

detention only, retention only, multipurpose