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4. PLRM Modeling Capabilities
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The following discussion highlights the modeling capabilities for the PLRM; organized into sections representing the PLRM Interface and each element of the pollutant load simulation (i.e. HSC, PSC, and SWT).
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PLRM Interface
The following are current capabilities of the PLRM Interface:
- Simple and intuitive data entry architecture
- Graphic representation of a project area
- Multiple catchment simulation
- Pre-processed Tahoe-specific input data and default input parameters that facilitate ease of use and consistency
- Flexibility for user override of default input parameters
- Summarized output for hydrology, pollutant loading, and storm water treatment
- Comparison of multiple scenarios to compute pollutant load reductions
- Automated flagging and reporting of user variations outside recommended ranges for sensitive input parameters
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Hydrology and Hydrologic Source Controls (HSC)
Hydrologic simulations in the PLRM include the following capabilities:
- Snowfall and snowmelt
- Effects of directly and indirectly connected impervious area, including routing directly connected areas to pervious areas
- Private property BMP implementation
- Infiltration and evapotranspiration, including accounting and reporting of volumes
For the hydrologic computations in the PLRM, pre-processed input data sets and default input parameters are provided to represent Tahoe Basin conditions. Pre-loaded input data sets include:
- Long-term meteorological data sets of precipitation and temperature at hourly intervals
- Snowmelt and snow management parameters
- Evapotranspiration parameters
- Hydrologic properties of soil from the Tahoe Basin Soil Survey (NRCS, 2006)
Pollutant Generation and Pollutant Source Control (PSC)
Pollutant generation in the PLRM is based on the product of average annual runoff and land use based characteristic runoff concentrations (CRCs).
Two separate methods are used to represent the implementation of PSCs, which can reduce the CRCS for 1) public right-of-ways (Road Methodology), and on 2) predominantly private land uses (Parcel Methodology). Capabilities for simulating pollutant generation and PSC implementation in the PLRM include:
- Road Methodology – a standardized approach that integrates physiographic characteristics, pollutant source control efforts, and pollutant recovery to predict the likely road condition and associated CRCs
- Parcel Methodology - a simple method to estimate improvements in CRCs from private property BMP implementation consistent with current regulations
Storm Water Treatment (SWT)
The reduction in pollutant loading achieved by a SWT facility depends on the portion of runoff treated and the extent of treatment achieved. The modeling approach calculates the percentage of runoff captured by the SWT from user entered design information and long-term simulations of hydrology. Runoff captured is assumed treated to a characteristic effluent concentration (CEC). Runoff that is bypassed is assumed to equal influent concentration. Current capabilities for SWT in the PLRM include:
- Representation of volume based and flow based SWT facilities based on key design criteria (e.g., water quality storage, drain time, water quality flow rate, infiltration rate, etc.)
- Representation of treatment trains
- Pre-loaded defaults for CECs based on Tahoe Basin data sets supplemented by data from the International BMP Database
- Flexibility for user specified CECs to represent advanced or innovative treatment
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