Your hands-on guide to approving MicroDrainage designs

Title Slide

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The webinar will be recorded and posted on innovyze.com along with the PowerPoint and Q&A document.

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Housekeeping

Today’s Presenter

Max Anderson

Product Manager (MicroDrainage)Innovyze

• Overview of ways we can approve MicroDrainage submissions.

• Investigation of some MicroDrainage submissions• PDF available on the ‘Handouts’ option See if you can spot some deliberate mistakes

• Discuss some of the key criteria when checking MicroDrainage designs

• Demonstration of Design Audit Wizard

• Upcoming Events

• As always, please ask questions!

Scope & Format

MicroDrainage - Applications

• New Residential Developments

• Highways Drainage

• SuDS design

• National Level Infrastructure Projects:• High Speed 2 Rail Link

• Queen Elizabeth Olympic Park

• Channel Tunnel

• Smart Motorways Programme

Poll Question 1

How frequently do you approve drainage designs?

• Understand current and future behaviour of site hydrology and response to typical events.

• Design a system to convey, control and cleanse discharge to a suitable point of outfall.

• Ensure a minimum level of service is provided by the system.

• Ensure that the design adheres to a variety of hydraulic performance and construction standards and that approval can be granted quickly.

• Design in a cost-effective manner without compromising performance.

• Mitigate / improve the water quality of runoff.

• Produce outputs and records of the design to enable construction, auditing, maintenance and asset management and a greater understanding of future flood risk.

Aims & Principles of Drainage Design

C3 Layout and Access

C3.1.1 Limit flood risk with layout of drains and sewers

C3.1.10 Minimum depth of cover;

a) 0.35m in gardens & pathways with no vehicular accessb) 0.5m domestic where <7.5t gross vehicle weightc) 0.9m domestic & mews where >7.5t gross vehicle wt

d) 0.9m in POS & agricultural lande) 1.2m in highways & parking areas >7.5t gross vehicle wt

C3.2.13 Manhole Diameters – must be designed to ensure suitable access.

C4 Reliability

C3.4.1 Minimum pipe size for SW sewer 150mm

C3.4.2 Minimum pipe size for SW lateral 100mm

C3.4.9 Minimum velocity 1 m/s at pipe full, or

a) 150mm @ minimum 1 in 150b) 100mm @ minimum 1 in 100

C Surface Water

Typical Design Standards – Sewers for Adoption 7th Edition

C5 Hydraulic Design

C5.1 Surface Water on Site

C5.1.1 Appropriate flow simulation method based on the Wallingford Procedure

C5.1.2 Design under pipe full to accept the following design storm without surcharging;

• Sites with average ground slopes >1% 1 year

• Sites with average ground slopes <1% 2 year

• Sites where consequences of flood are severe 5 year

C5.1.3 Runoff from roofs, roads & paved areas @ 100% impermeability

C5.1.4 Roughness value (ks) for surface water to be 0.6mm

C5.2 Protection Against Flooding

C5.2.1 No flooding for 1:30 year return period

C5.2.2 Underground storage to attenuate 1:30 year return period

C5.2.3 Locate storage tank for a free-flowing discharge

C5.2.4 Demonstrate flow paths and identify the flood routes

C Surface Water

Often also required to demonstrate performance in 100yr +CC% (i.e.

Exceedance Rainfall events)

Poll Question 2

What format or outputs do you most frequently use when reviewing /

approving drainage designs?

• Vital in identifying & avoiding pitfalls

• Can save valuable time, effort and money

• Requirement to provide information earlier in the design process, i.e. Pre-planning

• Need agreement on certain constraints e.g. discharge rates, design rainfall, coefficients

Early Consultation

SCOPE

QUALITY

Checking Design Criteria

• We need to ensure our networks can achieve a level of service

• We use rainfall theories to help design and assess network performance • Based on combinations of observed

data & statistics

• Geographic Variation

• FSR or FEH – specification of which rainfall theory is to be used at which stage.

Using ‘Design Rainfall’

FSR:FEH Rainfall Intensity Thematic map for 1hr 100yr storm[Red – FEH >> FSR Blue – FSR >> FEH]

Modified Rational Method Eqn:𝑄 = 2.78 𝐶𝑣 𝐶𝑟 𝐼 𝐴 (𝑢𝑠𝑖𝑛𝑔 𝑙/𝑠,𝑚𝑚/ℎ𝑟, ℎ𝑎)

Rainfall for pipe sizing

• Auto-design has been locked• MicroDrainage is unable to make changes

to satisfy design criteria• Need to consider cover levels

• For some pipes:Capacity < Flow

• Flow is calculated for each pipe based on design criteria rainfall & runoff parameters e.g. Return Period

• Capacity being less than Flow is a bad sign for being able to meet the no surcharge (but we need to simulate to confirm)

Modified Rational Method Eqn:𝑄 = 2.78 𝐶𝑣 𝐶𝑟 𝐼 𝐴 (𝑢𝑠𝑖𝑛𝑔 𝑙/𝑠,𝑚𝑚/ℎ𝑟, ℎ𝑎)

Checking Simulation Results

• Pipes are sized based on an estimation of an expected intensity for each pipe.

• Simulation allows us to see the response of the network when subject to the entire storm profile, i.e. Intensity (and inflow) is variable.

Simulation is different to pipe design!

Intensity

Time

RP – 1:1yr

RP – 1:10yr

FSR IDF Curves

Simulation Criteria

• Be clear in specification of parameters: MH Headloss, MADD Factor

• Be aware of double accounting CC% / additional flow %

• If Hydrographs / Controls / Storage structures are specified, check you have the details of these in the submission.

• Useful for identifying areas of storage within a large network model

• Can quickly compare to our Quick Storage Estimate

• Able to generate based on True Length or Centre-Centre

OK – Water level below pipe soffit

SURCHARGED – Water level above pipe soffit but below Flood Risk Level

FLOOD RISK – Water level above flood risk level but below cover

FLOOD – Water level above cover level

Pipe Status

• ‘Spikey’ appearance would indicate instabilities• Could be an issue with Analysis Settings or an

inherent modelling issue (flow controls not co-located with storage structures)

• Check the total simulation time• Here we’ve not yet seen the volume in the tank

reduce to ½ the peak so we would be unable to confirm Half Drain Time characteristics

• Can resolve this by editing Simulation Run-time

Viewing Result Hydrographs

How can we be sure we’re looking at the worst possible behaviour?

We would have to check every duration of storm and filter the results or use the critical results

summary!

Demonstration in MicroDrainage

MicroDrainage Checking and Auditing Course:

13th December 2018

MicroDrainage SuDS Concepts & Design Course:

18th January 2019

Further MicroDrainage Courses:

http://innovyze.com/education/training_schedule/

Training Courses

• World Water-Tech, London, February 26-27th

Upcoming Webinar:

“Introducing InfoAsset Online”, 13th December

Upcoming Events

Poll Question 3

How many mistakes did you spot in the handout?

Thanks for joining us

Max AndersonProduct Manager (MicroDrainage)

+44 (0) 1635 582 555TELEPHONE:

education@innovyze.com

WWW.INNOVYZE.COM