Inlet Design

Reference : Queesland UrbanDrainage Manual(QUDM)

1. Inlet terminology
ㅇ In urban environment it is densly populated, Spatially constrained, Lots of vehicle, pedestrain. so It must control flooding frequent, unfrequent, rare events in safety aspects.
ㅇ Longidudinal Drainage
- Combination of stormwater inlets and interconnected pipes is needed
- Majority of Aus systems discharge into creek, rivers or the ocean
- To reduce flooding, need strategy transfer overland flow into underground
   > based on calculations and flood estimation
   > provide convenience and safety
   > Capture water for re-use
ㅇ stormwter inlet
  - Two classification
     > Sag inlet(water come from both direction)
     > On-grade inlet(pit on the grade water com froe one side)
  - Many names(gully/side entry pits, Field/drop inlets, Kerb openings)

ㅇStorm Frequency
- Minor storm
    > underground flow
    > Longitudinal drainage system
  - Major storm
    > Overland flow
    > Road reserve or drainage channel
 
 

ㅇKerb inlet
  - kerb inlet(side  entry pit)
  - Grated inlet
  - combination inlet(gully pit)

ㅇField inlet(drop inlet)
  - need to be maintained(many debris can be in it)
  - Flush-mounted grate
  - Elevated grate
  - dome screen

*longitudinal : 세로방향의
*sag : 축 처진

2.Flow Limits
ㅇ Before designing inlet, we need to know
   - how much flow approaching to pit(ensure flow with, depth, (depth x velocity))
   - Vihicle consideration (safe for a vihicle in parking line?)
   - pedestrian consideration (how well can they flow beside the bus stop?)

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ㅇFlow limits half road capacity

- Izzard's Equation
 > one method
 > based on manning's equation
 >estimate half road capacity
 > Qa = approach flow

  
3.Flow Termiology
ㅇ Qc : Catchment flow
  - Consists of only catchment for the inlet pit
  - we need to understand Obtain contours, Survey, Site visit 
  - Road fall place needs on-grate pits / Road has a low point needs sag pits
  - Lots grade to or away from road
  - Road crests push water in opposite dirrection
  - water runs along the kerb on both sides of the road and kerb returns direton flow around intersection
ㅇ Qi : inflow
 - total inlet captures and conveys underground through pipe network
 - inlet capture charts are needed to caculate inflow
ㅇ Qb : bypass flow
  - remaining flow that is not captured by inlet(Qb=Qa-Qi)
ㅇ Qa : Approach flow
  - if inlet is top of catchment, Qa=Qc
  - if inlet has upstream catchment, Qa=Qc+Qb
 
* consist of ~ 로 구성되다 / contour 등고선 / intersection 교차로

4. Inlet Caputre Charts
ㅇ mathmatical equations can estimate how much stormwater an inlet can capture(laboratory testing can prove with results)
ㅇ hydralic capture charts(each place need to have their own chart) created from equations or test results and it allow engineer and designers to predict behaviour of stromwater inlet

ㅇ Sag Condition
 - Hydrulic performance based on ponding depth above inlet opening and Physical dimensions of inlet's Kerb and Grate opening
 - Inlet chart :  it shows capture flow(L/s) according to its Depth at invert of Channel

   > technically It shouldn't make any bypass
   > e.g. If Qa = 250L/s, and if you use gully pit(red line) it's depth should be 126mm

 

ㅇ On-grade condition

  - it's hydraulic performance based on Dimension of inlets
   > water can be alowed to pit's pipe or
   > the more it's grade, the more it's bypass
   > the more it's crossfall, the mire it's bypass
   > e.g. If it the Qa is 250L/s and road grade is 1%, it can capture 160L/s and it's bypass gonna be 90L/s

 

 

ㅇ beside of these, many common problems can be encoutered
   - Various inlet configuration, Blockage factors, severe storm.