Continuous Watershed Modeling - Storm Management System
QHM is a Windows 95/NT-based continuous watershed quantity and quality simulation model intended for watershed management and stormwater design. The program can also be used as an effective teaching tool.
Most applications have been in consulting assignments that involved watershed analysis usually related to selection and sizing of stormwater BMPs, particularly, flow control and treatment ponds.
- Elements of a system that can be represented by the model include watershed processes, reservoirs, control ponds, and streams or channels.
- Watershed quantity processes include Surface Runoff, Base Flow, Winter Runoff, Soil Freeze-Thaw, Snowmelt, and Snow Removal.
- Watershed water quality processes include soil erosion and urban runoff pollutants.
- Simulation of stormwater control ponds includes flow routing, mixing, transport, removal, bypass, and treatment by sediment removal and first-order reduction processes.
- Routing though reservoirs is represented.
- Channel processes include flow routing and quality effects including mixing, junctions, transport, distributed and point inputs, and streambank erosion.
- QHM quantity and quality simulations can be performed using time steps of 5 minutes to 24 hours for input, calculation, or output; the basic time step is hourly. Although QHM is a continuous simulation model, it can be used for event simulation.
- Input data - precipitation, temperature, and flow - can be in one of several common formats.
- Duration of the simulation period is limited only by available disk space.
- QHM output includes time series, graphics, and statistics representing input and output data.
- Model calibration is facilitated by the ability to compare total flow volume and sediment loads, maximum and minimum flow rates and pollutant concentrations, and concentration frequency statistics for a specified period.
- QHM can be customized for specialized applications by arrangement with the developers.
QHM offers an important planning and design tool to watershed managers and designers of stormwater quantity and quality control systems.
QHM is capable of continuous simulation of:
Simulation can represent a period of indefinite length (limited only by available disk space). The model can be used on a discrete event or multi-event continuous basis.
- Surface runoff and base flow
- Detention pond routing
- Reservoir routing
- Soil freeze-thaw
- Snowmelt and snow removal/disposal
- Evaporation and evapotranspiration
- Pollutant generation and routing
- Stream erosion potential
Constituents that can be simulated are: stormwater runoff (flow rate and volume) and, optionally, none or any combination of: one pollutant exhibiting first-order decay or characteristics simulated using a rating curve; sediments (in up to 5 size fractions) characterized by discrete particle settling; and instream erosion indices based on cumulative excess boundary shear stress.
Appropriate flow and pollutant records obtained elsewhere (monitoring or other simulation models) can be routed through ponds or river reaches by the model.
Components of a physical system that can be simulated are:
A system comprised of any combination and any number of the above components can be simulated provided that each component of the system and the system as a whole can be described as "one-way" or "non-feedback."
- Detention ponds
- River reaches which may have junctions and bifurcation (flow splits)
Looping networks, or ponds where outflow depends on water depth in the receiving channel, are examples of situations which might not be well represented in this model. A typical application appropriate for QHM would be a dendritic river network with channels adequately represented by uniform flow conditions.
QHM Frequently Asked Questions
1. What water quality parameters are represented?
QHM can represent a pollutant that exhibits first-order decay or characteristics that can be represented by a rating curve; sediment, characterized by size fractions; and in-stream erosion indices based on cumulative excess boundary shear stress.
2. What system of units is employed?
Input files must be metric except for USGS flow files which use English units. Output is metric.
3. What about calibration?
The CALIBRATE command in QHM will compare simulated and recorded flow or pollutant data series and calculate comparative statistics. Other output options can also be used for visual and statistical comparisons.
4. What is the simulation time step?
The basic time step is one hour, but simulations can also be carried out using time steps of 5, 10, 15, 20 and 30 minutes, and 24 hours.
5. QHM is a continuous model; can it simulate a single event?
Yes. QHM can be used as an event model if desired.
6. Is there a limit on the duration of simulation?
No. The duration of a QHM simulation period is limited only by the availability of input data and available disk space.
7. What are the input data requirements?
Sample input data files are provided with QHM. Most simulations require precipitation and evaporation data files, in standard formats. Temperature data is required for winter simulation. Physical characteristics of system elements must be described, e.g., depth-area curves for ponds and reservoirs. Some parameters must be estimated based on prior knowledge or experience, or are calibration variables. Recorded flow series can be provided as an input to a simulation run, or for model calibration. QHM can convert a data file from one standard format to another and remove "missing data" codes that are not recognized by the program.
8. Is information about model calibration parameters available?
QHM documentation provides some information and cites references related to calibration parameters. Sample input files provided with QHM may indicate the range of values that might be expected for a specific parameter, recognizing that the values may differ for another climatic or geographic region.
9. What is the input data structure?
In addition to the numerical data that is entered in prescribed formats, the QHM input file format allows the user to annotate the file with descriptive comments. Sample input files are provided with QHM.
10. What is the format of QHM output?
The QHM output file echoes information from the input file and summarizes simulation results. Program options allow listing or plotting of some output data and statistics in the output file. Complete flow or water quality series can be output to designated ASCII files. Statistics that can be generated about simulated or recorded data series include: total flow volume, maximum and minimum flow rates and pollutant concentrations, concentration frequency statistics, and number and duration of exeedances of specified flows and concentrations. Output results can be presented in one of two graphic formats.
11. Can the user access the program code?
No. QHM documentation describes the algorithms on which the program is based with appropriate references. For specialized applications, customized modifications of the program can be prepared.
12. What documentation accompanies QHM?
QHM includes an on-line user's manual and is accompanied by a hard copy version of the manual and technical notes that summarize, with references, the theoretical basis for program algorithms.
13. Is QHM user-friendly?
QMH has been designed to be user-friendly. The user's manual includes appendices that provide step-by-step guidance through basic applications, and sample input and data files illustrate basic file structure and can be used in sample runs. (The user is expected to be familiar with the hydrologic and water quality concepts on which any water management model is based.)
14. To what extent has QHM been tested and applied?
QUALHYMO, the program from which QHM is derived, has been tested and applied over the past 15 years in the U.S., Canada and Europe. Program documentation includes references to some of this work. Development of QHM has included extensive testing and practical applications of initial versions of the program.
15. What about upgrades and revisions?
Development of the QHM program has benefited from the knowledge, experience, and advice of dedicated users over the past 15 years. Users are encouraged to share their problems and advice which will provide the basis for further improvements to the program. Registered users will be informed of problems, solutions, and QHM upgrades.
486/Pentium running Microsoft Windows 95/NT and at least 2 MB of free RAM.
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Τελευταία Ενημέρωση 27 Ιουλίου 2004 - Last Revised on July 27, 2004
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