Cloud_Based_SWMM_Modeling_Design_Specifications
Cloud Based SWMM - Modeling Design Specifications
Table of Contents
Section One SWMM Parameters and Functions
Section Two Real-time modeling considerations with SWMM
Section Three Model calibration using SCADA Data in real time simulation
Section One
SWMM Parameters and Functions
Rainfall
Rainfall Files
SWMM's rain gage objects can utilize rainfall data stored in external Rainfall Files. The program currently recognizes the following formats for storing such data:
- DSI-3240 and related formats which record hourly rainfall at U.S. National Weather Service (NWS) and Federal Aviation Agency stations, available online from the National Climatic Data Center (NCDC) at www.ncdc.noaa.gov/oa/ncdc.html.
- DSI-3260 and related formats which record fifteen minute rainfall at NWS stations, also available online from NCDC
A standard user-prepared format where each line of the file contains the station ID, year, month, day, hour, minute, and non-zero precipitation reading, all separated by one or more spaces.
An excerpt from the user-prepared format might look as follows:
STA01 2004 6 12 00 00 0.12
STA01 2004 6 12 01 00 0.04
STA01 2004 6 22 16 00 0.07
This format can also accept multiple stations within the same file.
When a rain gage is designated as receiving its rainfall data from a file, the user must supply the name of the file and the name of the recording station referenced in the file. For the standard user-prepared format, the rainfall type (e.g., intensity or volume), recording time interval, and depth units must also be supplied as rain gage properties. For the other file types these properties are defined by their respective file format and are automatically recognized by SWMM.
Rain Gage Properties
Designated in SWMM Rain Gage Dialog Box
Data FILE
-File Name: Name of external file containing rainfall data.
-Station No: Recording gage station number.
-Rain Units: Depth units (IN or MM) for rainfall values in user-prepared files (other standard file formats have fixed units depending on the format).
* Time interval for data (.dat file or timeseries) must be specified correctly for each rain gage. Issues were seen if this is set to incorrect values.
Forum Post on the subject: http://www.chiwater.com/BBS/forums/thread-view.asp?tid=3560
- If rain interval is specified as 5 min, but data is hourly:
- incorrect large intensity spikes are seen for 5 minutes
- hour rain data is applied over a single 5-min period
- If rain interval is specified as 1 hr, but data is 5 min:
- incorrect low intensity results are seen throughout
- 5-min rain data is applied over a constant hour period
* Rainfall .dat files are interpreted in the following manner:
- Rainfall.dat has hourly interval rainfall and a value of 0.01 at 1am
- SWMM reads that as 0.01 of rainfall occurring between 1am and 2am!
Rainfall .dat files can contain data at different time intervals for different gages.
This was verified with an experimental run.
1. A new Rainfall.dat was created by combining KCVG 1-hr data with MCWT 5-min data.
2. New rainfall.dat was loaded into the Mill Creek model in SWMM5
3. One rain gage was changed to point to the 5-minute MCWT data (by changing Time Interval to 0:05 and Station ID to MCWT)
4. The model was run for around 9 hours, and the precipitation for a subcatchment assigned to KCVG gage was plotted next to a subcatchment assigned to the MCWT gage
5. Values were verified by looking at the rainfall.dat for each gage and converting from volume (in) to intensity (in/hr) plotted above.
System Rainfall graph is based on combining all subcatchment rainfall using their individual areas.
SysResults[SYS_RAINFALL] += (REAL4)(SubcatchResults[SUBCATCH_RAINFALL] * area);
Forum Link: http://swmm2000.com/profiles/blogs/swmm-5-precipitation-options
Junctions Inflow
Direct
Alternative to subcatchment runoff calculation. These are assigned to junctions and represent runoff inflow directly into the system.
Supply: Baseline x Pattern or Timeseries
Dry Weather
Dry Weather (sanitary) flow in the network. These are assigned to select junctions (often representing inflow from an area.
Supply: Average Value x Patterns
RDII
Rainfall Inflow and Infiltration flowing into a selected junction.
...
Other Terms
- lateral inflow (runoff + all other external inflows, in flow units)
- total inflow (lateral inflow + upstream inflows, in flow units)
Simulation
Kinematic Wave
- Simplified simulation: often faster run times
- Kinematic Wave Routing is generally viewed as the conservative approach
- Typical approach for Master Planning
- Kinematic –numerical stability with large time steps (5 to 15 minutes)
Dynamic Wave
- Theoretically less conservative because of less simplifications to the Saint Venant Equations
- Typical Approach for Design Projects
- Dynamic –numerical stability with smaller time steps (less than one minute)
HOTSTARTS
HOTSTART files can be created by:
1. Save Interface file: saves state of end of simulation
2. Export Hotstart: saves state of current time in simulation
HOTSTART files can be used by:
1. Use Interface file: sets initial conditions
HOTSTART only saves certain aspects of the state of the collection system:
1. Depth and flow in junctions/conduits is preserved
2. Pollutant concentration in junctions/conduits is preserved
3. Hydrology conditions (subcatchment properties, runoff, etc.) is NOT preserved
Dropbox: Using Hotstart files in SWMM5 (Functionality&Limitations)
Units
Switching units is handled in SWMM by changing flow units in bottom left corner of SWMM5 or by changing value in input file. However, it was noticed that changing units (from MGD to CFS) does not convert existing inflows. Namely Dry weather inflow units change but the values are not converted, therefore causing incorrect values. To successfully convert flow units, one would also have to manually convert all inflow values (DWI and Direct).
Real time modeling
Zimmer, Schmidt, Ostfeld, and Minsker, "New Method for the Offline Solution of Pressurized and Supercritical Flows" J Hydraulic Eng. 2013.
"Real-time portrayal of sewer system hydrology and hydraulics requires a fast computational model"
"The SRM results imply that controlling the weir outflow at locations upstream of the flow bottleneck by adjusting gate positions throughout the model may be critical to minimizing overflows in real-time operational strategies."
"Computational analysis for three historical storm events and 12 design storms of different intensity and duration show the temporally implicit hydraulic representation to have a lower computational time than the SWMM dynamic wave model. The reduced duration is attributed to lookup table interpolation for conduit, weir, and sluice gate flow and backwater effects. The decreased computational time will prove valuable during real-time control of larger combined sewer systems in which many possible sluice gate positions are analyzed within a finite forecast horizon."
Section Two
Real-time modeling considerations with SWMM
Parameters that can be adjusted/updated
1. Climate Data
a. Rainfall time series
b. Evaporation time series?
2. Initial Levels
a. Storage Units
b. Junctions
3. Initial Flow
a. Conduits (flow monitors)
4. Pump Status
a. On/Off
b. Time/level based rules
5. Orifice setting
a. Fraction open (based on the storage levels OR Link flow OR RTC’s)
b. Set by time/level controls
c. Also available for weirs
6. Tidal Curve
a. Time series for river stage (elevation)
b. Simulation of river intrusions
7. Other Considerations
a. Dry weather flow –
i. Inflow rate to nodes
ii. Time patterns for inflow
b. Infiltration/Inflow rates
c. Snowmelt
i. Temperature
ii. Evaporation
iii. Windspeed
Also Important to Real Time modeling
1. SCADA display
a. Storage/Outflow Levels
b. Flow monitors
Section Three
Model calibration using SCADA Data in real time simulation
This details the potential ways to calibrate a collection system model using SCADA data in a real-time simulation. Required first is initial tuning/calibration that can locate miss-modeled structural elements:
I. First Fine-Tuning/Calibration - Modifying Structural Parameters
a. Typical non-real-time system calibrations (dry weather, wet weather, etc.)
b. Pipe size - Based on the flow and velocity measurements from flow monitors, conduit size can be back-calculated and updated in the model to rectify estimated/incorrect pipe sizes.
c. Invert levels - Based on the level measurements at multiple locations, large anomaly in the invert levels can be detected and rectified.
Required afterwards are sets of calibrations/adjustments that would be leveraged with the incoming real-time SCADA data:
II. Setting Initial Conditions
a. Using SCADA data in a real-time simulation, initial conditions of the model parameters can be set in the model.
b. This includes initial flow in the conduits and initial levels in storage units/junctions/outfalls
III. Modifying Boundary Conditions
c. Tidal curves can be modified using real-time river stage data; this defines river intrusion into the system.
d. Input into the system: dry weather inflow. This is input at junctions, and the magnitude/pattern can be updated in the model in real-time simulation during dry weather if flow monitors are present at the incoming pipes of these junctions.
e. Also input into the system: runoff from subcatchments. This input is driven by subcatchment parameters (imperviousness, infiltration, etc.) and rainfall. Rainfall is updated in real-time, and it may be possible to update subcatchment parameters to achieve flow monitor equivalency for SCADA vs. Model during wet weather.
IV. Modifying Internal Conditions
a. Pump status/curves can be calibrated using nearby tank level sensors or by using flow data at or nearby the pump.
b. Orifice/Sluice gate settings (% open) can be adjusted using nearby level/flow based monitors.
c. Outflow/storage levels could be adjusted to match SCADA data, but this could cause balance issues and is not recommended.
See Also: Model Calibration Process for general sewer network calibration process - Dropbox Link73iwn9/Model%20Calibration%20Process.docx)