Lecture 8

Question 1

what was the historical stormwater management approach

Answer 1

drainage efficiency
get it out as fast as possible

Question 2

what are some impacts of development on urban stormwater graph

Answer 2

the post development hydrograph has a sharper peak and a lesser lag time

Question 3

increased peak flows cause

Answer 3

channel alteration and pathogens

Question 4

reduced infiltration causes

Answer 4

sedimentation and nutrients

Question 5

reduced groundwater recharge causes

Answer 5

disruptions to benthic habitat and inorganics (metals,salt)

Question 6

lower baseflows cause

Answer 6

elevated water temperatures and toxic organics

Question 7

what are ecological maintenance flows (EMFs)

Answer 7

the streamflow required to maintain aquatic habitat

Question 8

what are the methods for defining EMFS

Answer 8

q90/q95 flow duration indicies

7Q2,7Q10,7Q20 7 day average minimum flows that occur once on average, every 2, 10, or 20 years.

Aquatic baseflow (ABF) method
0.005m^3/(s-km^2) used by USFWS for small ungauges basins in new england

Question 9

in atlantic provinces the EMF is

Answer 9

25% mean annual flow
75% median monthly flow

Question 10

how do EMFs vary

Answer 10

by flow condition (severe degradation to flushing or maximum)

and time of year
(october to march) and (april to september)

Question 11

fair or dgreading rec ommended EMF has

Answer 11

most substrate submerged

Question 12

poor or minimum recommended emf has

Answer 12

50% of stream substrate submerged

Question 13

kuhn marsh study is where

Answer 13

headwater catchment within morris lake watershed

Question 14

kuhn marsh characteristics

Answer 14

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

Question 15

kuhn marsh stormwater quantity and quality

Answer 15

16 month study
baseflow and stormflow loading of
nutrients
bactera
metals
organic carbon
assesment of wetland function

Question 16

kuhn marsh water quality issues

Answer 16

nutrient loading
elevated E coli
heavy metals

Question 17

Stormwater management objectives

Answer 17

Peak flow management
Water quantity management
water quality management

Question 18

the first step in stormwater management is to

Answer 18

identify the design objectives

Question 19

most jurisdictions will specify the objectives that the

Answer 19

stormwater management systems must meet

Question 20

why manage peak flow?

Answer 20

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

Question 21

what does managing water quantity mean

Answer 21

designing a system to manage a specific volume of stormwater

(example 2yr-24hr storm to be retained for no less than 24 hours)

Question 22

why manage water quantity

Answer 22

reduce peak flows
provide water quality treatment
possibly allow for infiltration

Question 23

what does water quality management mean

Answer 23

systems are designed to remove a specific amount of contaminant load (typically sediments)

could be specified as a 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 24hr)

Question 24

Control strategies for stormwater management

Answer 24

1. Lot level controls
   (source control) (less than 2 hectares)
2. End-of Pipe Controls
   -large scale infrastructures.

Question 25

Lot level controls consist of what sub-approaches

Answer 25

1. temporary strorage 2. infiltration and long-term storage and reuse

Question 26

what are the two kinds of temporary storage lot level controls common in NS

Answer 26

parking lot storage rooftop storage

Question 27

Infiltration/long term lot level controls include

Answer 27

dry wells cisterns infiltration trenches infiltration swales rain gardens pervious pavement

Question 28

the primary goal of long term level controls is

Answer 28

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

Question 29

lot level infiltration systems challenges/considerations

Answer 29

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

Question 30

end of piipe control strategies

Answer 30

detention and retention ponds constructed wetlands infiltrations basins engineered filtration systems

Question 31

detention vs retention ponds (IMPORTANT)

Answer 31

detention ponds are used to dampen peak flow rates retention ponds are 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 (i.e a 2yr 24hr storm)

Question 32

A retention pond for 20 ha residential development in HRM would have a foodprint of

Answer 32

approximately 2 hectares

Question 33

what is the most widely applied stormwater management tehcnology

Answer 33

retention and detention ponds

Question 34

retention and detention ponds types

Answer 34

can be designed as either wet or dry ponds can also be designed as an infiltration basin

Question 35

what are constructed wetlands

Answer 35

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

Question 36

what depths do constructed wetlands need, why

Answer 36

they need a depth of <1m to allow for vegetation establishment, therefore wetlands typically need to be quite large in order to achieve required retention times for treatment

Question 37

limitations of the road reduction approach

Answer 37

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

Question 38

detention/retention pond design

Answer 38

can be detention, retention, or as multipurpose systems wet or dry design L:W >3:1 permanent pool depths in wet ponds are typically 1-2m

Question 39

how would create a trial design for a detention/retention pond

Answer 39

there is a nifty formula that relates desired outflow hydrograph peak to desired inflow hydrograph peak