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Showing posts from December, 2008

SWMM 5 Pond Infiltration

You can model the pond infiltration indirectly by using either:

1. a Pump Type 4 (the classic SWMM 4 solution to this matter), in which the Pump simulates the pond depth - infiltration rate function,

2. alter the SWMM 5 Evap Factor for a pond so that you have seasonal or monthly variation in your infiltration loss simulated as an increase in Pan Evaporation or

3. You can use the newer SWMM 5 Outlet structure and use either a functional or tabular relationship to simulate the infiltration loss as a function of pond depth.

If you search the CHI Knowledge database you can also find some suggestions from Mike Gregory (and others) about modeling infiltration loss from a pond. I would recommend items 2 and 3 because "An outlet curve in SWMM 5 has the same functionality as a SWMM 4 Depth related pump ( Flow versus Depth) but it has the great advantage of being explicitly designed to have multiple functions; does not have the appearance of being an ad hoc solution (as a pump simulating infil…

SWMM 5 Variable Time Step

SWMM 5 Variable Time Step

In the SWMM 5 Simulation Options/Dynamic Wave Options is the Variable Time Step Frame which contains the Adjustment Factor Percentage. The Adjustment Factor is a multiplication factor on the CFL condition.

The effiect of changing the Adjustment factor can be seen in the following graph. As the value of the adjustment factor changes from 75 to 50 to 25 the time step used in the program decreases because the time step gets further away from the CFL time step condition.

SWMM5 Normal Flow

Option "Define Supercritical Flow By" does inside the SWMM 5 engine. The options are called Slope, Froude and Bothin the GUI and in the engine of SWMM 5. A few other variable definitions you need to know to understand this explanation are: (1) Y1 for the upstream link depth, (2) Y2 for the downstream link depth, (3) Q for the flow in the link, (4)Qfull for the full Manning's equation flow or normal flow for the link based on the bed slope, (5) Froude1 and Froude2 for the Froude Number respectively of the upstream and downstream ends of the link, (6) n for Manning's roughness, (7) Yfull for the maximum depth of the link and (8) Qnormal for the Normal Flow equation flow based on the upstream area of the link (A1) and the upstream hydraulic radius (R1).

In the SWMM 5 engine these options are used after the dynamic wave equation flow is estimated using the St. Venant equation. The option that you choose is only active for those links that have a flow greater than 0, links…

Smaller Storms Drop Larger Overall Rainfall In Hurricane Season

Smaller Storms Drop Larger Overall Rainfall In Hurricane Season

ScienceDaily (Dec. 11, 2007) — Researchers have found that when residents of the U.S. southeastern states look skyward for rain to alleviate a long-term drought, they should be hoping for a tropical storm over a hurricane for more reasons than one. According to a new study using NASA satellite data, smaller tropical storms do more to alleviate droughts than hurricanes do over the course of a season by bringing greater cumulative rainfall.

A new study that provides insight into what kind of storms are best at tackling drought in the southeastern United States. The study focuses on a decade of first-ever daily rainfall measurements by a NASA satellite carrying a weather radar in space. The study's authors believe the same insights can be applied by meteorologists and public officials to other regions where daily satellite rainfall data and storm tracking data are available.

In the wake of Hurricane Katrina, meteorologis…