INTRODUCTION TO EPA SWMM 5.0
Rodrigo Concha Jopia FLUMEN Research Institute
Technical University of Catalonia UPC
Introduction: What is EPA SWMM 5.0?
EPA SWMM
Environmental Protection Agency Storm Water Management Model
SWMM is a distributed dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and
quality from primarily urban areas
SWMM’s Process Models Precipitation
Snowmelt
Surface Runoff
Evaporation/ Infiltration
Groundwater
Overland Flow
Channel, Pipe & Storage Routing
Washoff
Sanitary Flows
RDII
Treatment / Diversion
Buildup
Key Hydrological Features
User-defined subcatchment areas Spatial Representation
Heat Balance/Degree Day Model Snowmelt
Localized Two-Zone Flux Model Groundwater
Nonlinear Reservoir Overland Flow
Horton Method Green-Ampt Method
SCS Method
Infiltration
User supplied Interception/Evaporation
User supplied Rainfall
Process In SWMM 5
Key Hydraulic Features
Overflow or Ponding Flooding
Rule-Based Controls Modulated Controls (including PID)
Variable Speed Gate Opening
Controls
Steady Flow Kinematic Wave (nonlinear form)
Dynamic Wave (semi-implicit)
Flow Routing
20 common shapes + irregular open channels + custom closed conduits
Conduit Shapes
Nodes (Junction, Storage, Outfall) Links (Conduits, Pumps, Regulators)
Drainage Elements
Key Water Quality Features
User-defined functions Drainage System Treatment
CSTR model Drainage System Routing
User-defined, Sanitary DWF, RDII inflow Non-Runoff Loads
User-assigned percent reduction BMP Removal
Rate proportional to runoff and buildup or can use an EMC
Pollutant Washoff
Power, exponential or saturation function of time Pollutant Buildup
Process In SWMM 5
Typical Applications of SWMM • Design and sizing of drainage system components
including detention facilities • Flood plain mapping of natural channel systems • Control of combined and sanitary sewer overflows • Generating non-point source pollutant loadings for waste
load allocation studies • Evaluating BMPs and LIDs for sustainability goals
SWMM version timeline
1971 - SWMM 1 (M&E, UF, WRE) 1975 - SWMM 2 (UF) 1981 - SWMM 3 (UF & CDM) 1983 - SWMM 3.3 (PC Version) 1988 - SWMM 4 (UF & CDM & OSU) 2004 – SWMM 5 (EPA & CDM)
∗ No sediment transport and erosion routines ∗ No pollutants routing in receiving waters and in the
sub-surface flow ∗ It is a hidrological-hydraulics analysis tool, not an
automatic design tool ∗ No direct linkage to GIS
SWMM 5.0 Limitations
Program structure
Example of .INP file
SWMM 5 Objects
∗ Visual Objects: elements that constitute the drainage system
∗ Non visual Objects: several data (tables, timeseries, etc.) neccesary in order to peform simulations
Conceptual modeling scheme used by SWMM 5
Atmosferic compartment Precipitation falls on the
Land Surface compartment Land Surface
compartment Important hydrological
process are modeled Rainfall losses Surface runoff
Conceptual modeling scheme used by SWMM 5.0
Groundwater compartment Receives infiltration from
Land Surface compartment Transport compartment Network of conveyance
elements: channels, pipes, manholes, etc.
Use of Nodes and Links in order to represent this network
Key parameters for subcatchment objetcs
Node – Link network representation(from Roesner et al.,1992)
Nodes
Links
Non visual object categories
Hydrology Climatology Aquifers Snow packs
Hydraulic Transects Unit Hydrographs Control Rules External Inflows
Water Quality Pollutants Land Uses Treatments
General Curves Time Series Time Patterns
Basic steps developing a new SWMM 5 project from scratch
Specify a set of options and common object properties (Measurement units, offsets, etc.) Draw a scheme of your catchment (or
network) using Visual Objects Edit the properties of Visual Objetcs that
make up your project Select a set of simulation options Run a simulation View the results of the simulation
Precipitation in SWMM 5.0: Rain Gage object
∗ Using a user-defined external datafile (Data File) ∗ Using a time series (Time Series): ∗ entering “by hand” both the rainfall and time values ∗ importing data from an external file ∗ Copying and pasting from a spreadsheet
Rainfall input data: two options
Rain Gage: mininal data requiered
∗ Rain Gage name ∗ Rain data format ∗ Time interval between each rain
data ∗ Way to feed Rain Gage with the
rain data: Timeseries or External File
20
Rain data format in SWMM 5
21
Rainfall losses in SWMM 5
∗ Three types of rainfall losses can be modeled: ∗ Evaporation ∗ Depression storage ∗ Infiltration
∗ All subcatchments contained in a project use the same infiltration model
∗ User should select these models according to his/her knowledge of the catchment (types of soils, land uses, measured data, etc.)
Evaporation and Depression storage
∗ Used at daily scale modeling (it is a slow process)
∗ Useful for continous modeling studies
∗ Not applied for a single storm event
It corresponds to a volume that must be fill prior to the ocurrence of any runoff
It represents initial abstractions such as surface ponding, interceptation by vegetation and surface wetting
Evaporation Depression storage
Infiltration in SWMM 5
∗ Process applied only on the pervious area of each subcatchment
∗ Three infiltration models
∗ User should select the model according to the degree of knowledge of the catchment
∗ While better it is the knowledge of the catchment, it is possible to use models of greater number of parameters
∗ Data input in each Subcatchment editor
∗ Empirical method ∗ Model of 3 parameters
∗ Drying Time: number of days for a fully saturated soil to dry completely
∗ Max Volume: Maximum infiltration volume possible
∗ Two last parameters are used in continuos modeling
Horton infiltration method in SWMM 5
∗ Physically-based method ∗ 3 parameters although the
last one is the difference between soil porosity and initial moisture content. So, 4 parameters are necessary
∗ G-A is not a popular method used in urban hydrology studies
Green–Ampt infiltration method in SWMM 5.0
Curve Number (CN) infiltration method in SWMM 5
∗ Derived from (but not the same as) the well-known SCS Curve Number method used in simplified runoff methods
∗ A derived equation from the classical SCS method is used:
where ∗ P, precipitation; R, potential runoff ; S, maximum soil
potential moisture retention, and CN, Curve number ∗ Total infiltration (F) can be computed as
2PRP S
=+
F P R= −
1000 10SCN
= −
∗ One parameter model: CN ∗ The parameter called
Conductivity is not used in computations anymore
∗ User should use tables to get CN values according to type of soil, land uses, etc.
Curve Number (CN) infiltration method in SWMM 5 (II)
Surface runoff model in SWMM 5
I(t): Inflows
O(t): Outflows
S: Storage volume
Q: Surface runoff
W: Subcatchment width
dp: Depression storage
d: Water depth
So: Subcatchment slope
n: Surface roughness coefficient
5 03
( ) ( )
( )p
dSI t O tdt
SQ W d d
n
− =
= ⋅ − ⋅
Each Subcatchment is treated as a Nonlinear Reservoir
H
ho
i (t)
H
ho
i (t)
H
ho
i (t)
i(t) = Rainfall – (Infiltration + Evaporation)
Surface runoff model in SWMM 5 (II)
Subcatchment width in SWMM 5
Subcatchment is conceptualized as a rectangular surface that has a uniform slope and a width W that drains to a single outlet channel
Initial estimate is given by
where, A: Subcatchment area Lfp: length of the longest overland flow path Maximum Lfp in rural areas: 150 m For urban catchments Lfp could be the
length from the back of a representative lot to the center of the street
If the overland flow length varies greatly within the subcatchment, then an area-weighted average should be used
W is often used as a calibration parameter due to it is not always easy to determine
Another way to determine W: subcatchment contribution width to the main closer conduit
𝑊𝑊 = 𝐴𝐴𝐿𝐿𝑓𝑓𝑓𝑓
Subcatchment width in SWMM 5
• DiGiano et al. (1976) • Subbasin=subcatchment
Hydraulic routing models used by SWMM 5 1. Steady Flow:
instantaneous traslation of a hydrograph from the upstream end of a conduit to the downstream end with no time delay or change in shape
2. Kinematic Wave: uniform unsteady flow, using the continuity equation and the normal flow condition
3. Dynamic Wave: this method solves the complete 1D Saint Venant equations for the entire conveyance network, allowing to the user simulate all gradually-varied flow conditions (backwater, surcharged flow and flooding)
0
0
SSxQ
tA
f =
=∂∂
+∂∂
0
0
2
=⋅⋅+⋅⋅+∂∂⋅⋅+
∂
∂
+∂∂
=∂∂
+∂∂
Lf hAgSAgxHAg
x
AQ
tQ
xQ
tA
0SS f =
Steady Flow model in SWMM 5
∗ Estimation just for some cases
∗ Steady Uniform flow ∗ Useful only to pre-design
the conveyance network, not to make the final design of the network
∗ Only applied to dentritic conveyance networks
Kinematic Wave flow model in SWMM 5
∗ Appropiate for steep slope conduits,
where there are supercritical flows ∗ It should not change the shape of the
hydrograph (if do, this is because of numerical reasons)
∗ It not take in account the downstream boundary conditions
∗ From a numerical point of view, more stable than Dynamic Wave method
Dynamic Flow model in SWMM 5
SWMM 5.0 uses a explicit finite difference numerical scheme in order to solve…
… the complete 1D the Saint Venant equations at each Conduit and…
… a continuity relationship at each Node
This model requires small time steps (Δt between 30 and 1 second usually)
Nodal flooding options in SWMM 5: Ponding Off and Ponding On
All excess inflow to node is lost from the system
All excess inflow to node is ponding on it. When adjacent conduits recover its conveyance capacity, then ponded volumen will be reintroduce to them
SWMM 5 web
http://www.epa.gov/nrmrl/wswrd/wq/models/swmm/
Information and uselful help (manuals, source codes, updates) for downloading
New update
Top Related