StormCAD BasicsMal Sharkey

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Part 1

• Intro to StormCAD

What is a Storm Sewer System?A storm sewer system is composed of surface components (e.g., gutters and inlets) and subsurface components (e.g., pipes, manholes, inlet boxes)

Storm Sewer Design• Storm sewer design and analysis consists of 2 basic

parts:− Surface flow calculations− Subsurface flow calculations

• Surface flow calcs evaluate the capacity of gutters (i.e., gutter spread and depth) and inlets (for inlets on grade, part of the flow, called “bypass flow,” will not be picked up and will continue down to the next inlet).

• Subsurface flow calcs evaluate the capacity of the subsurface pipes to prevent flooding. Storm sewer pipes should always point downhill, and the systems are branched (i.e., typically, there should not be loops).

Storm Sewer Design

P a rk in g L o t a n d R o a d w a yS to r m S e w e r C o ll e c t io n S y s t e mSA M P L E 4

S a m p le 4

J a n 2 0 0 3Ha e s ta d M e th o ds In c .

S h e e t 1 / 1

P-P

L2

P-O2

I- 4R

J- 2

I- PL2I- PL1

J- 5

I- 3L

I- 4L

I- PL3

I- 3R

Outlet

J- 1

I- 2R

I- 1R

I- 1L

J- 3

J- 4

E l e va t io n (f t )

S ta t i o n ( f t )

Profile : I-1 l to O utlet

S c e n a r i o : 1 0 0 - y e a r S t o rm

0 + 0 0 1 + 0 0 2 + 0 0 3 + 0 0 4 + 0 0 5 + 0 05 0 5 .0 0

5 1 0 .0 0

5 1 5 .0 0

5 2 0 .0 0S u m p : 5 1 3 .5 3 f tR im : 5 1 8 .2 0 f tL a b e l : I -1 L

S u m p : 5 1 3 .5 1 f tR im : 5 1 8 .4 0 f tL a b e l : J- 1

S u m p : 5 1 1 .1 5 f tR im : 5 1 6 .9 0 f tL a b e l : J- 2

S u m p : 5 1 0 .8 0 f tR im : 5 1 6 .8 0 f tL a b e l : I -2 R

S u m p : 5 1 0 .7 2 f tR im : 5 1 8 .2 0 f tL a b e l : J- 5

S u m p : 5 0 8 .6 0 f tR im : 5 1 0 .6 0 f tL a b e l : O u t le t

S : 0 .0 0 1 5 0 0 f t / f tS i ze : 8 in c hL : 1 3 .0 0 f tD n . In v e rt : 5 1 3 .5 1 f tU p . In v e rt : 5 1 3 .5 3 f tL a b e l : P - 1 L

S : 0 .0 2 2 5 1 3 f t / f tS i ze : 8 in c hL : 1 0 5 .0 0 f tD n . In v e rt : 5 1 1 .1 5 f tU p . In v e rt : 5 1 3 .5 1 f tL a b e l : P - C 1

S : 0 .0 2 6 9 2 3 f t / f tS i ze : 1 5 in chL : 1 3 .0 0 f tD n . In v e rt : 5 1 0 .8 0 f tU p . In v e rt : 5 1 1 .1 5 f tL a b e l : P - 2 R

S : 0 .0 0 1 5 0 0 f t / f tS i ze : 2 4 in chL : 5 5 .5 0 f tD n . In v e rt : 5 1 0 .7 2 f tU p . In v e rt : 5 1 0 .8 0 f tL a b e l : P - O 1

S : 0 .0 0 8 9 5 0 f t / f tS i ze : 2 4 in chL : 2 3 6 .5 0 f tD n . In v e rt : 5 0 8 .6 0 f tU p . In v e rt : 5 1 0 .7 2 f tL a b e l : P - O 2

Subsurface (pipe) layout

Profile View

Plan View Surface (gutter) connectivity

Gutters

• Flow typically travels to storm sewer inlets though gutters

• The engineer is interested in the width and depth of the gutter flow, and has to make sure that neither is excessive.

• Gutter flow is analyzed using a form of Manning’s equation

Inlets• Three common inlet types are grate inlets, curb inlets, and

combination inlets.• Inlets may be located on a continuous grade or in a sag location• Inlets on grade do not intercept 100% of the flow that comes to them

—some of the flow bypasses and goes to the next inlet downgrade• HEC-22 calculation methods are used to determine gutter spread

and depth and inlet capacity

Storm Sewer Profile

StormCADStorm sewer design & analysis with inlet modeling

StormCAD

Applies to:− Commercial site design− Land development− Roadway drainage design− Planning, mapping, and inventories for

larger areas (e.g., municipality)

StormCADCapabilities

− Uses rational method hydrology

− Performs gradually varied flow profile analysis

− Incorporates HEC-22 methods for inlet and gutter capacity calcs, including gutter spread and bypass flow calcs

− Performs automated pipe & inlet design

− Includes GIS and database connections

− Generates profile plots and tabular reports

− Includes MicroStation & AutoCAD integration options

− Includes Scenario Management

User Interface

Drawing Area

Scenario

Layout Tools

Graphical Tools

Zoom ToolsCompute Button

Tabular Reports

Element Symbology

BackgroundLayers

Basic Data EntryLayout Toolbar

Pipe Tool

Right-click menu to change element type

Property Grid

FlexTables

• Sort• Filter• Global Edit• Customize

ModelBuilder: Using External Data Convert CAD lines, polylines, and blocks

Connect to any

database & keep it in sync with

your modelConnect to shapefiles

Part 2

• Getting familiar with StormCAD

A little more theory…Open Channel Flow

•Open channel flow is flow that has a free water surface open to the atmosphere.•It occurs in natural rivers and streams, manmade ditches and channels, gutters, and gravity-flow pipes.

Gutter

Conservation of Energy•In open channel flow, the pressure head term (p/γ) is replaced by the vertical flow depth y•The energy equation between sections 1 and 2 for the channel shown is written as:

Lhzg

Vyz

g

Vy 2

22

21

21

1 22

Open Channel Flow Definitions

Normal Flow− If a channel shape remains constant for a long enough

distance, the flow will reach a constant “normal depth.”

Varied Flow− Flow depth typically varies along the length of a channel due

to factors like changing channel shape or flow depths other than normal depth on the upstream or downstream end.

− Varied flow can change gradually along a channel (“gradually varied flow” or GVF) or rapidly (in the case of a hydraulic jump).

Supercritical vs. Subcritical Flow− These are the 2 basic flow types possible for flow in an open

channel.− Supercritical flow is shallow, high-velocity flow− Subcritical flow is deeper, slower-velocity flow− Flow can transition from subcritical to supercritical flow, or

vice versa− Between supercritical flow and subcritical flow is the “critical

depth.” This value can be determined for any channel and used to classify the flow type. Sometimes, it is also used as a starting point (boundary condition) in GVF calculations

Open Channel Flow Types

Normal Flow

Transition from Subcritical to Supercritical flow

Transition from Supercritical to Subcritical Flow (Hydraulic Jump)

Graphic Output

Color Coding

Annotation

Profiles

Data Management

Network Navigator

Queries

Selection Sets

Part 3

• Analysis in StormCAD

Rational MethodTo compute a peak flow rate from a watershed, a method such as the Rational Method can be used:

Q = c × i × A− Q is the peak discharge from the drainage area

− c is the “runoff coefficient” (the fraction of rainfall that is converted to runoff)

− i is the intensity of the rainfall for a design storm event having a duration equal to the drainage area “time of concentration”. This can be obtained using intensity-duration-frequency curves for the locale (see below).

− A is the area

Inlet Calculations

Perform inlet capture & bypass calcs using HEC-22 methods

Set up gutter

networks

Store inlet properties in an engineering

library

Multiple Scenarios

Create alternative input data sets with Alternative Manager

Model a variety of situations using

Scenario Manager

Active Topology

Before site is developed (proposed elements are inactive)

After site is developed

Viewing OutputFlexTables

Reports

PropertyGrid

MicroStation & AutoCAD IntegrationStormCAD can run inside MicroStation or AutoCAD

StormCAD BasicsMal Sharkey