Drains Guide Part 1 - Standard Hydraulic Model

8/12/2019 Drains Guide Part 1 - Standard Hydraulic Model

1/17

A Short Guide to DRAINSPart 1 (January 2011) Watercom Pty Ltd1

A GUIDE TO DRAINSDEMONSTRATION EXAMPLES

PART 1 STANDARD HYDRAULIC MODEL CALCULATIONS

Geoffrey OLoughlin and Bob Stack

July 2011

1. Introduction

This guide will help you to navigate through the examples that can be run with the DRAINSdemoprogram. This version has all the features of DRAINS, but cannot model more that five pipes or openchannels, five sub-catchments and one irregular open channel link. There are also limitations on thechanges that can be made to detention basins, culverts and storage routing models.

The examples are divided into ones that run with the DRAINSstandard hydraulic model, which arediscussed here, and those for the premium hydraulic model, which are covered in Part 2 of the Guide.The standard model applies unsteady flow hydraulics to pipe and open channel flows, with simplercalculations for overflows. The premium model applies unsteady modelling to pipes, open channelsand overflow routes. (These models replace an earlier hydraulic procedure called the basic model,which is now obsolete,)

You can refer to the Help system installed with DRAINS, and the DRAINSmanual is available as aPDF file from www.watercom.com.au. DRAINSis updated regularly and the latest version can bedownloaded from the Watercom website.

A DRAINSViewer program is provided free. This enables persons reviewing or checking models toinspect inputs and results from any DRAINSmodel file.

2. What DRAINSDoes

DRAINSwas originally developed as a general-purpose Windows application to design and analyse

piped urban stormwater drainage systems. Additional capabilities have been added, including achoice of hydrological and hydraulic models. DRAINScan apply:

(a) ILSAX hydrology, and rational method and storage routing procedures, to convert rainfall inputsto stormwater runoff;

(b) extensive hydraulic procedures, to route flow hydrographs through pipes, overflow routes andopen channels, calculating hydraulic grade lines and other characteristics;

(b) detention basin routing.

DRAINSallows you to enter data describing a drainage system graphically, using drawing tools ortransfers from CAD, GIS, digital terrain modelling (DTM) programs and spreadsheets. It calculatesrates of stormwater runoff from catchment areas during storms and directs flows through the drainage

system model. In design runs it sets pipe sizes and invert levels to prevent excessive spilling frompits. In analysis runs, it simulates the behaviour of drainage networks and indicates areas whereflooding occurs. Components and layouts of systems can be changed and additional runs made toimprove drainage designs.

3. Installation

DRAINSworks on PCs running the Microsoft Windows operating systems from 95 to Windows 7. It

can be installed by clicking on Dr ai nsSet up. exeand following the instructions in the Installationprocedure, inserting the password DEMO. This will install the program and example files described

below in a C: \ Pr ogr am Fi l es\ Dr ai ns\ Demo folder on your PC. The program can be

uninstalled using Uni nst al l a pr ogr amoption in the Control Panel.


2/17


4. Using DRAINS

On most PC systems the installation process will put a DRAINSicon on the Pr ogramsfolder in your

Start menu, and you can start DRAINSby clicking on this. If this icon is not present, you can create

Shortcut icon on your Desktop linking to the program in the folder C: \ Pr ogr am

Fi l es\ Dr ai ns\ Demo\ Pr ogr am. Clicking on this icon starts the program.A window with a large blank space appears. At the top there are seven menus and a toolbar:

Using options from the menus, you can set up and run a DRAINSmodel in four steps:

(a) using options in the Projectmenu to define hydrological models, rainfall patterns and otherparameters, to set up storms for design and analysis, and to establish data bases for pipes, pitsand overflow routes;

(b) setting out a drainage network using the drawing tools from the toolbar, or inputting drawing,spreadsheet or GIS file data using options in the Fileand Editmenus,

(c) saving the data using Filemenu options, and then performing calculations in Design and Analysisruns initiated in the Run menu;

(d) reviewing the results using options from pop-up menus for individual components and the Viewmenu; and printing and exporting results to spreadsheets, drawing and GIS programs using theFileand Editmenus.

You can copy various graphs and tables to a spreadsheet or word processor via the Windowsclipboard. You can also produce long section drawings of the pipe system for export to CADprograms.

The DRAINStoolbar contains drawing tools, grouped into nodes, links and sub-catchments. If youclick on one of these, the cursor will change to a pencil, which can be used to place that component inthe drawing window. For, example, you can use the pit and node tools:

to draw two drainage pits and an outlet node, as shown below:

These can be connected by pipes, by selecting the pipe tool and clicking at the beginning and endpoints of each pipe. Overflow paths can be added as poly-lines, and the names of components(containing question marks to start with) can be dragged to more convenient locations.

Sub-catchments can then be added, making sure that they touch the pits:

In this way, a connected drainage network can be constructed, with nodes at the outlets. Thecomponents and their names can be moved by dragging them around the screen. A pipe, channel or

overflow route can be moved as a single unit by dragging near its centre, or its ends can be movedindividually.


3/17


Data for components is entered and edited using property sheets, which appear when you right clickon a component, and select Edit Datafrom the pop-up menu, as shown below.

Figure 1 Pop-Up Menu and Property Sheet for a Pit


4/17


5. Design and Analysis Methods

Design

If you were to apply DRAINSto a greenfields subdivision drainage system design, you might work outthe plan of the system on a paper plan, or more likely, using a CAD or DTM program. You might alsouse the links between DRAINSand the DTMs 12d, MX and Autodesk Advanced Road Design for thispurpose.

You would then set up a DRAINSmodel, probably with a background showing street layout andcadastral data. You would probably start with a pre-existing base file that already contains thehydrological, rainfall, pipe, pit and overflow route information that you need, in data bases accessiblefrom the Project menu. It is likely that the pipe layout and background would be imported from asuitable CAD file.

Following procedures in design manuals such asAustralian Rainfall and Runoff(Institution ofEngineers Australia, 1987) you would set up a set of minor storms, which define the conditions thatare to be addressed in sizing drainage systems. You would also set up a set of major storms, to beused to check that the system 'fails safe' in severe conditions. Minor storms may have averagerecurrence intervals (ARIs) of 2 to 20 years, while major storms are usually 100 year ARI.

After running the DRAINSmodel using the design method, and checking this with an analysis usingminor storms, you could transfer the system data (containing the data entered through propertysheets, plus designed pipe sizes and invert levels, and x-y coordinates of pits and nodes) to aspreadsheet program using the option in the Editmenu, and copy this on to a worksheet labelled"Data". The results of the design run using minor storms could be transferred to another worksheetlabelled 'Design' or 'Minor'.

After inspecting the design results, you could then run DRAINSwith the major storms to check that thesystem operates safely in large storm events, and transfer the results from these to another worksheetlabelled 'Analysis' or 'Major'. The three worksheets provide the documentation for the design.

You could then produce long sections of selected pipelines, and transfer these to a CAD program as aDXF file. If you were using a DTM program, you could transfer data directly from DRAINSand use themore elaborate drawing facilities that they provide.

Designing for infill developments where there are constraints imposed by existing developments andinfrastructure is a more complicated process, and it may not be possible to use the automaticprocedures that apply in greenfields design. Since DRAINSoperates quickly, and changes are easilymade, it can be used to arrive at a solution by trial and error searching.

Examples 1 to 5, 7, 11 and 12 show various design situations and methods.

Analysis

Analysis techniques, involving the simulation of flows from catchments and their passage through

drainage networks, are used as part of design procedures in DRAINS, and can also be applied toestablished stormwater drainage systems, determining whether parts of these have the capacity tocarry flowrates from various storms, and defining possible overflow rates and flow characteristics.

DRAINSoffers two methods of assessing established drainage systems the standard hydraulicmodel, which provides quick estimates suitable for most assessments, and the premium hydraulicmodel that provides more rigorous and detailed modelling of surface flows, as discussed in Part 2 ofthis Guide.

Modelling existing systems requires more hydrological and hydraulic information than the design ofnew systems. Information for setting up models to analyse established drainage systems will comefrom plans, inspection sheets, aerial photographs, survey data and other sources held by a council ordrainage authority, and from its asset data base and GIS. A GIS, CAD or DTM program will be

needed for defining sub-catchment boundaries and areas and other inputs.


5/17


Sites will need to be inspected and unusual drainage configurations will have to be set up in DRAINS.It may take a lot of work to set up a file for a large, complicated system, but once this is established, itcan easily be updated and re-run, becoming a tool for assessment of drainage system adequacy,especially in the consideration of flood-affected development sites. The spreadsheet output inDRAINS, which can also act as a data input, can be used to facilitate the editing of data, and fortransferring data and results to data base and GIS programs.

See Examples 6 and 8 for analysis applications. Also note that analysis is used for checking in all the

design examples.

Broad-Scale Modelling of Rural and Urban Catchments

The storage routing option in DRAINSallows users to model large catchments in a similar manner tothe "runoff routing" programs, RORB, RAFTS and WBNM, using catchments and the stream reachesthat connect them as non-linear storage flow routing elements.

These can be used to determine flows at many points within a catchment. In a typical rural study, themodel would be set up on the basis of catchment topography and the pattern of the stream network. Ifgauging data were available, the model would then be calibrated by adjusting the routing parametersfor the selected model type until there was good agreement between the hydrographs produced by themodel and gauged catchment hydrographs. Following this, the model could then be applied with

larger design floods to assess the flows at critical locations.

The facilities in DRAINSexpand on those available in earlier programs, because it is possible to runsome sub-catchments with ILSAX hydrology and others with storage routing hydrology at the sametime. Situations such as an urban drainage system influenced by tailwater from a large stream can beconsistently modelled. DRAINSalso offers the choice of modelling stream hydraulic grade linesexactly by specifying open channels, or by routing flows through a routed stream reach.

See Examples 9 and 10 for applications of storage routing models.

6. Example Files using the Design Procedure

These are installed together with the DRAINSprogram. From DRAINS, example files can be read

using the Openoption in the Filemenu. They are located in the folder C: \ Pr ogr am Fi l es

\ Dr ai ns\ Demo\ Dat af i l es. When examining and running them, you can open on-line Help at anytime by pressing the F1 key, or selecting Contentsfrom the Helpmenu.

We recommend that you test the features of DRAINSby going through these examples, which all workwithin the limitations mentioned at the beginning of these notes. You can then alter the examples orset up some simple systems to extend your understanding.

Example 1 - Major/minor design for a small drainage system at Gymea, SutherlandShire, NSW(File Gymea ILSAX Example - Standard.drn)

The DRAINSmain window shown in Figure 2 presents a system of five pipes and six pits or nodesagainst the background of a street and cadastral (property) data. The land is assumed to slope fromtop to bottom. A property sheet defining the inputs for one of the sub-catchments is also shown.

Two storms have been defined. A 5 year ARI, 25 minute design storm is used in a design run withILSAX hydrology to establish pipe sizes and invert levels, and in an analysis run to check these in amajor 100 year ARI storm. The design procedure is based on a method from the Queensland UrbanDrainage Manual, 1992 that defines the pit sizes needed to safely limit the flowrates along eachoverflow route.

Initially, the names of pipes start with ?? because pipe diameters and invert levels have not beenentered in the property sheet. This partial entry of data is permitted because a Design run willdetermine appropriate pipe diameters and invert levels.


6/17


Figure 2 DRAINSMain Window showing Gymea System and Rainfall Pattern

After a Design run is made and results are expected, the designed systems can then be used in anAnalysis run employing a 100 year ARI, 25 minute storm to check the adequacy of this system duringa major storm.

Figure 3 shows that the names of components have been changed to colour-coded numerical results,such as peak flowrates through pipes and maximum water levels at pits. Significant concernsaddressed in the design are avoiding flows over road low points at the two sag pits, and preventing

excessive flows along street gutters or channels. This analysis was performed using the standardhydraulic model. With the demonstration version of DRAINSit is also possible to run the premiumhydraulic model, which provides more accurate results for surface flows, such as flows along overflowroutes and ponding of water at sag pits.

PeakPipe

Flowrate(blue)

Peak OverflowFlowrate

(red )

Peak Sub-CatchmentFlowrate(black)

Peak HGLLevels(green)

Names ofComponents


7/17


Figure 3 Output from an Analysis Run with Minor Storms Following a Design Run

Results can be inspected using options in the pop-up menu to display flow hydrographs, HGL plotsand long-sections, as shown in Figure 3. Then the designed system can be modelled in an analysisrun with a 100 year ARI, 25 minute storm to check the adequacy of the system during a major storm.The analysis in Figure 3 was performed using the standard hydraulic model. With the demonstrationversion of DRAINSit is also possible to run the premium hydraulic model, which provides moreaccurate results for surface flows such as flows along overflow routes and ponding of water at sag

pits.

To explore the example, we suggest that you follow these steps:

In the Project menu, examine the Hydrological Model, Rainfall Data and other options, cancellingeach dialog box or property sheet to ensure that the data is not changed.

Right click on a component and select Edit Datato view the property sheet data for thatcomponent

Run the Design option in the Run menu and inspect the results from the 5 year ARI storm. (Peakflows for sub-catchments, pipes and overland flow paths and water levels at pits are presented ascolour-coded numbers.)

Run theAdvanced Design (pits and pipes)option in the Run menu,

SelectAnalyse major stormsandAnalyse minor storms from the Run menu and inspect theresults for the 100 year ARI storm.

For individual pits and pipes, use the pop-up menu to examine hydraulic grade line positions andflow hydrographs. Check the Long sectionoption. You can also use the Export DXF LongSectionoption in the Filemenu to specify a route (such as Pipe A.1 to Outlet) and send a DXFdrawing of a pipe long section to a CAD program, as shown below.

Figure 4 Pipe Long Section Plot Produced by DRAINS


8/17


9/17


Results are similar in most respects to those from Example 1, although the calculated peak flows arelower, being calculated from rectangular rainfall blocks rather than theAustralian Rainfall and Runoffrainfall patterns used by the ILSAX model. As with the first example, you can export results to aspreadsheet and produce long-sections, such as that shown in Figure 6.

Figure 6 Major Storm Results from Gymea Rational Method Example, with Street Flow Disp lay

Example 3 - Major /minor design for the System at Gymea, NSW, using theExtended Rational Method(File Gymea Rational Method & ERM

Example - Standard.drn with the ERM hydrological model chosen)

This method, shown in Figure 7, was developed to model detention basins using a method that wasconsistent with the rational method, since it is usually impossible to adjust an ILSAX model to matchrational method peak flows for a range of average recurrence intervals and storm durations.

The operation of the model is almost exactly the same as when using ILSAX hydrology. WhenAustralian Rainfall and Runoffstorm burst patterns are used this method will generally produce higher

peak flowrates than the rational method peak flows.

Example 4 - Multiple storm analysis using part of an example fromAustral ian Rainfal l and Runoff(File Penrith ARR87 Example -

Standard.drn)

This example, shown in Figure 8, includes the top five pipes in the pipe drainage design example fromChapter 14 ofAustralian Rainfall and Runoff(Institution of Engineers, Australia, 1987). It is similar toExample 1, except that eight 2 year ARI design storms are used in the Design run and eight 100 yearARI storms are used for Analysis. In addition, overland flow paths in the sub-catchments are definedin more detail, using a constant time + kinematic wave calculation, rather than a constant time of entry.We suggest that you explore the drainage system and results in the same way as for the first example.

DesignCriteria


10/17


Figure 7 Extended Rational Method Results with Output of Results

Figure 8 Penrith Example wi th an Overflow Route Hydrographs


11/17


Example 5 - An On-Site Stormwater Detention System at Sydney, NSW(File Sydney OSD Example - Standard.drn)

This example involves a property drainage system for a dual occupancy development on a 800 m2

house lot with an on-site stormwater detention (OSD) storage at the outlet, shown in Figure 9.

Figure 9 Sydney OSD Example showing Routing Results for a Three Design Storms

The land falls from west to east. A new house is to be constructed in a backyard. The detention basinis situated on and near the driveway running past the original dwelling, located to the right. Flows inand out of the basin are through pipes. Invert levels must be specified for the pipes entering orleaving the detention basin, but other pipes can be designed by DRAINS. In this example UPVCpipes are selected from the Pipe Database. You can add additional pipe and pit types to the data basefrom the Editmenu.

Actually, two systems are presented the pre-development situation, represented by a single sub-catchment and node located to the left, and the more detailed, post-development situation. DRAINSallows separated systems to run side by side with the same hydrological model and rainfall data, tomake easy comparisons. Three storms are used in Design and three in Analysis.

The storage is defined by an elevation-surface area table, which can be prepared in a spreadsheetand pasted into DRAINS. (A Utility Spreadsheet, downloadable from www.watercom.com.au, can beused to prepare various inputs to DRAINS, such as rainfall patterns, hydrographs and rating curve(elevation vs flowrate) relationships.

The storages, orifice sizes and other factors can be varied to arrive at the most efficient design. Pre-and post development results can be compared storm by storm, as the worst case result may bemisleading.

Note how DRAINSdeals with the high-level or overflow outlet from a detention basin. These arecontrolled by information specified for the overflow path, rather than for the basin itself. This exampleis set up with a high early discharge pit. You can run the model with and without this to see thedifference it makes.

Pre-Development Model


12/17


Example 6 - A Model of an Established Drainage System near Brisbane, Queensland(File: Beenleigh Existing Example - Standard.drn.)

This example shows how DRAINScan be applied in the modelling of an established stormwaterdrainage system, where overland flows are blocked by fences and other barriers. A detention basin isused to model an unintended stormwater storage area located behind commercial buildings.

The DRAINSmodel is shown in Figure 10. The location is occupied by small factory and warehouse

units. The fall of land is from the north-west to the south-east. The site shown hatched represents abuilding re-development that has shut off an overland flow path, causing surface stormwater to pondbeside the building and to escape by two possible routes. This situation is modelled as a detentionbasin with one low-level pipe outlet and two high-level weir outlets. All pipe inverts must be fullyspecified, and the run is made as an Analysis run with major storms. One of the pipes has arectangular cross-section. Note how overflow routes are linked via a node.

Figure 10 Beenleigh Example showing Detention Basin Routing

The run with major storms determines the division of flows as they escape from the trapped pondingarea along the two escape routes. You can export data and results to spreadsheet.

Example 7 - Mixed Pipe and Open Channel System at Bendigo, Victoria, with aDetention Basin(File Bendigo Trunk Drain Example -

Standard.drn)

This system, shown in Figure 11, involves pipe and artificial channel links including a detention basin.Pipes connect into open channels via nodes, for which surface levels must be specified, so that designcan proceed. This capability of integrating varied components and systems is one of the mostpowerful features of DRAINS.


13/17


Figure 11 Bendigo Mixed Pipe and Open Channel Model with a Detention Basin

Example 8 - Hypothetical Open Channel System at Bowen, Queensland,with a Culvert, Bridge and Irregular Channel Reach(File Bowen Channel & Stream Example - Standard.drn)

This example shows how DRAINScan calculate the afflux occurring at culverts and bridges, and

determine water surface profiles along irregular channel sections. The system is shown in Figure 12.

Figure 12 Bowen Stream Model with a Culvert, Bridge and Irregular Open Channel


14/17


With the standard or premium hydraulic models, only one cross-section is specified for the irregularchannel. For greater accuracy, the reach could be divided into segments, but this is not done here asthe limit of five channels available with the Demonstration version of DRAINSwould be exceeded.

The standard and premium hydraulic models give the same results for this system.

Example 9 - Rural Catchment at Shepparton, Victoria, modelled using

RORB type storage routing procedures(File Shepparton RORB Rural.drn)

This model is set up for a purely rural catchment using the RORB type of storage routing model. Thehydrological model and sub-catchment data entry are different to those for ILSAX models. Some datais entered in the sub-catchments and some in the stream reaches. Reaches do not have levelsspecified. They only route flows and hydraulic grade levels are not provided. Detention basins can beadded, and the model can be linked to open channels that are completely-defined.

When the model runs, it produces hydrographs as shown in Figure 13 and indicates clearly the degreeof flow routing that takes place in each reach.

Figure 13 Shepparton RORB Model showing Non-Linear Routing Results

The examples also include variations on this Shepparton model using RAFTS and WBNM hydrology.

Example 10 - A Model that Mixes ILSAX and WBNM Storage Routing Models(File Bowral Rural-Urban Example - Standard.drn)

This example shows how DRAINScan apply two hydrological models in the same model. A smallurban area is modelled using ILSAX hydrology, while the stream to which it drains is modelled usingWBNM hydrology. In the calculations, both hydrological models are operated at the same time step.


15/17


Figure 14 Bowral Example combin ing ILSAX and WBNM Hydrology

Here the stream levels do not define a tailwater level for the pipe system, but this can be done byadding open channel sections into which the WBNM model flowrates can be directed. Water levelswill be calculated in these and will define a variable tailwater level for pipe systems.

Example 11 - Queensland Urban Drainage Manual Procedures(File South Pine River Rational Method Example with US Flow Paths.drn)

This rational method example, shown in Figure 15, transposes the earlier Gymea example to theBrisbane area, adding nodes and overflow routes above the top pit of each pipe branch. Theseadditional components allow the designer to assess approach flows to pits at the tops of pipelines.

It also demonstrates the QUDM (Queensland Urban Drainage Manual) procedure for determining pitpressure change coefficients. Once a set of flowrates are calculated, a procedure in the Run menucan be applied to adjust the coefficients using charts from QUDM, providing details of the chart andlook-up values used.

A special Check HGL spreadsheet output sets out results, including those from the overflow routes atthe tops of branches, and a spreadsheet converter can be used to set out results in formats requiredby Queensland councils, as shown in Figure 16.


16/17


Figure 15 South Pine Rivers Example showing Approach Flow Characteristics

Figure 16 Rational Method Outputs in QUDM Formats

Example 12 - Property Drainage Example(FileMerimbulah Apartment - Standard.drn)

This example describes a property drainage system with downpipes modelled as nodes and slopingdownpipes as pipes. The surface levels at nodes can be roof gutter levels or ground surfaceelevations. Since both above- and below-ground pipelines may need to be designed, it is necessaryto specify the invert levels and size of the first pipe in each branch.

As shown in Figure 17, pipe long-sections may show roof gutter or surface levels, with the Survey

Levels... option in the Pipe property sheet being used to add points that clarify the long section plotsby showing the edges of buildings.

Indicates how muchof the catchment flowoccurs along this flow

path


17/17

A Short Guide to DRAINSPart 1 (January 2011) Watercom Pty Ltd

Figure 17 Design of an Apartment Bui lding Piped Drainage System, showing Long-Section

7. Exploring DRAINS

DRAINSis being constantly augmented, and contains additional features that have not been

described here. After looking through the examples, you might investigate DRAINSfurther by varyingthe data specified in the examples or by creating examples of your own, within the limits imposed inthis demonstration version. Updated versions will be posted on the website, www.watercom.com.au,from which the DRAINSManual and design aids can be downloaded.

For additional information, and to obtain the DRAINSViewer, please phone or fax enquiries to BobStack on (02) 6649 8005 or e-mail [email protected].

Information on training workshops held in state capitals can be obtained from Geoffrey O'Loughlin on0438 383 841 and [email protected].

Date post:	03-Jun-2018
Category:	Documents
Upload:	gregn5
View:	219 times
Download:	0 times

Drains Guide Part 1 - Standard Hydraulic Model

Documents