Urban Drainage Chapter 1-3 Highlights Flashcards
Sewerage!
Combined sewer problems?
Backups and Flooding
Waste sewer problems?
illegal connections lead to exceedance
Storm sewer problems?
Urbanization,increased runoff, increased erosion, damaged ecosystem, rainfall isn’t clean (atmosphere scrubbing)
Current sewer problems?
Built at different times, residual problems, lots of different solutions needed
Four quality characteristics and effects?
- SS - block light, stops photosynthesis, kills life
- Oxygen demand - storm water can introduce life that increases this
- Nutrients - Promotes algae
- Heavy metals - toxic compound in urban runoff
Source control aim and pros?
To imporve quantity and quality
Are cost effective and site specific
Three types of collection system controls?
- Sewer Separation
- Sewer flushing
- In-system control
Sewer separation as a collection system control notes?
overflow/backup imporved
expensive
Whats is sewer flushing?
A collection system control
Summer flow leave a buildup that can be removed with flushing
What is In-system control
A collection system control
Diverts water from high to low capacity areas in real time
moderate cost for significant improvement
Five types of storage/treatment option?
- Outfall - combined
- Outfall - storm
- Interceptor capacity
- Offline storage
- Flow balancing system
What is Outfall - combined?
A storage/treatment option
needs of be small, treat lots of water quickly
unlikely to be solely used but can be used in conjunction
What is Outfall - storm?
A storage/treatment option
Detention ponds can recharge GW and remove contaminants
Can restrict outflow
Uses settlement
What is Interceptor capacity?
A storage/treatment option
Combines system for treatment to make the most of economies of scale
Larger pipe doesnt relate to reductions CSO reduction
(CSO - combined sewer overflow)
What is Offline storage?
A storage/treatment option
Diverting water to low capacity areas off the system to be pumped later
What is a Flow balancing system?
A storage/treatment option
cheap and easy to expand
uses pontoon and curtain to divert water
Name two major issue with IDF curves and the rational method
- AEP rainfall isn’t AEP flood
2. Makes hyetograph a rectangular trace of constant intensity
Four reasons AEP rainfall isn’t AEP flood event?
- It doesn’t take into account antecedent soil conditions
- Storms are made of many characteristics
- Doesn’t consider time or spatial variation of the storm
- Doesn’t consider snow melt events
Notes on having a system made of many elements?
Things may be sensitive to different parameters so shouldn’t just be designed to full range of conditions
Explain Figure 3.3 and Figure 3.4
The same peak discharge should have one return periods but given two
The same hyetograph should have two different return periods but given one
Three alternatives to AEP?
- Continuous analysis (CA)
- Analytical Probabilistic Modeling (AP)
- Stochastic Modeling Techniques (SM)
What is CA?
A alternative to AEP
Uses long term records as input to get long term statistics
Storage relies on time variations (infiltration capacity, depression storage)
Can tell us performance through time under different meteorological conditions
Can do antecedent conditions
What is AP?
A alternative to AEP - Analytical Probabilistic Modeling
Uses statistics of long term meteorological event as input to get long term statistics (drainage performs etc)
Used to screen and plan
computationally simple
What is SM?
A alternative to AEP - Stochastic Modeling Techniques
Uses Monte Carlo to generate long term data sets
Is numerical not analytical
