Date: Thu, 2 Dec 2021 16:27:12 -0800 (PST) Message-ID: <2066361770.2962.1638491232227@HILLINCONF.xps.xpsolutions.com> Subject: Exported From Confluence MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_Part_2961_1041562892.1638491232212" ------=_Part_2961_1041562892.1638491232212 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Location: file:///C:/exported.html Analysis of SWC/Junctions

# Analysis of SWC/Junctions

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## Muskingum

Muskingum routing is used in xpdrainage to represent channelled flow or = filtered flow. It is suitable for drainage systems with significant time of= travel between inlet and outlet and some flattening of the hydrograph, eit= her because of long channelled flow, or because flow is filtered slowly. It= is available for all SWCs except the Soakaway. The description of the meth= od here is also relevant for the flow routing through Connections. The Musk= ingum routing method is based on the two following equations.

The equation of continuity of flow is: The model of storage in the channel/reach/pipe/system is: Where:

• I is inflow

• Q is outflow
• S is reach storage
• K represents travel time through the reach
• =CE=B8 is a weighting coefficient

These can be converted to a routing equation relating outflow to inflow = over the timestep from time to time&= nbsp; that can be computed simply as: These simple equations are well suited to represent flow through sustain= able drainage systems because of the natural choice of states and parameter= s (natural in terms of the design process). First of all, maximum storage i= s either a design aim or can be estimated easily. Similarly, travel time is= either a design aim or can be approximated fairly simply using a friction = loss equation and length between input and output locations.
The weighti= ng coefficient is more difficult to estimate. 0.5 is the maximum possible v= alue and gives no dispersal of the hydrograph (translation only). Values be= tween 0.2 and 0.4 are recommended for natural channels. 0.4 would be a reas= onable default for swales and 0.2 for bioretention systems. Even a value of= 0.0 is possible, giving more spread. Note that the spread is symmetrical.<= br>For sustainable drainage systems, the travel time is calculated both alo= ng the length of the system and down through the filter layers. This is don= e as a simple calculation of along + down, where along is along the fastest= route through the system (along channel for a swale and through bottom dra= inage layer for bioretention).

While the Muskingum method gives the output hydrograph value at every ti= mestep, it does not calculate levels. As it is essential for the user to kn= ow the levels within the storage system, how full the system is at each tim= estep, and whether it will overflow or not, xpdrainage calculates the water= levels in each structure from the current stored volume, after the volumes= have been updated.This allows the software to show the hydraulic grade lin= e.

xpdrainage also offers the following two alternatives to the Muskingum m= ethod for the routing through the Stormwater Controls.

## Simple Time Delay

While some degree of attenuation is natural with most storage devices an= d gravity conveyance systems, it is not always clear what should be the deg= ree of flattening of the hydrograph, and the user may prefer to just specif= y a time delay. The hydrograph is propagated through the structure with a l= ag but with no attenuation. This is actually calculated as a particular cas= e of the Muskingum method when the weighting coefficient =CE=B8 is equ= al to 0.5.

Note that overall the SWC can still generate some flow attenuation in th= is case if the outlets restrict the outflow.

## No Delay

Alternatively the user can specify the routing to be calculated through = the structure without any delay.

Note that overall the SWC can still generate some flow attenuation in th= is case if the outlets restrict the outflow.

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Workflow - What's next...? Connect&= nbsp;Inflows&nb= sp;to your Stormwater Control, specify Inlets or Outlets or connect
to another Stormwater Control or Junction.

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