- #Et output different from pcswmm to epaswmm how to
- #Et output different from pcswmm to epaswmm manuals
- #Et output different from pcswmm to epaswmm manual
Only the latter area allows for rainfall losses due to infiltration into the soil.įigure 1-3. Each Subcatchment can be further divided into three subareas: an impervious area with depression (detention) storage, an impervious area without depression storage and a pervious area with depression storage. An idealized Subcatchment is conceptualized as a rectangular surface that has a uniform slope and a width W that drains to a single outlet channel as shown in Figure 1-3. SWMM is a distributed model, which means that a study area can be subdivided into any number of irregular Subcatchments to best capture the effect that spatial variability in topography, drainage pathways, land cover, and soil characteristics have on runoff generation.
#Et output different from pcswmm to epaswmm manual
Example 2 in this manual will add a conveyance system of swales, channels, and culverts to this model. Because this is an initial estimation of the discharges at the outlet of the catchment under its current and future conditions, no channelized flows will be defined and only runoff as overland flow will be simulated. Two models will be built: one that represents the catchment in its current undeveloped condition and one that represents the catchment after it is fully developed. These were supplemented with design guidelines published by the Denver Urban Drainage and Flood Control District (UDFCD) (UDFCD, 2001). Most of the parameter values used in this example were taken from tables published in the InfoSWMM H2OMap SWMM InfoSWMM SA Users Guide. The design storms used here will be for a 2-hour event with return periods of 2, 10, and 100 years.
#Et output different from pcswmm to epaswmm manuals
The approach typically employed in stormwater drainage manuals will be used, which is to compute the hydrologic response of the catchment to a series of synthetic design storms associated with different return periods. The objective is to estimate the stormwater discharges at the catchment’s outlet and compare them to the ones generated prior to urbanization. The developed site will drain to a stream through a culvert under the street located on the southeast side of the site, which is considered to be the outlet point of the catchment. However, the residential lots will be graded toward the street at a slope of 2% so they can drain easily. This implies that future streets will, in general, follow the natural slope.
With the exception of the depressions located in the parkland area, no major changes in topography are expected. Figure 1-2 shows the proposed development for this site. This undeveloped area is primarily pasture land that has a silt loam soil type. To meet environmental sustainability objectives, similar criteria are being applied to total runoff volume as well.įigure 1-1 is a contour map of a 29 acre natural catchment area where a new residential development is planned. Many local stormwater ordinances and agencies require that new developments limit peak runoff flows relative to those under pre-development conditions. Models of this type are very common in practice. Flow routing of runoff through the drainage pipes and channels contained within the catchment is addressed in Example 2. It illustrates the process of spatially dividing a catchment into smaller computational units, called Subcatchments, and discusses the characteristics of these Subcatchments that InfoSWMM H2OMap SWMM InfoSWMM SA uses to transform rainfall into runoff.
#Et output different from pcswmm to epaswmm how to
This first example demonstrates how to construct a hydrologic model of an urban catchment and use it to compare stormwater runoff under both pre- and post-development conditions.
Post-Development Runoff in InfoSWMM and InfoSWMM SA