Search the Community
Showing results for tags 'pit'.
Found 2 results
Q: I'm doing some checks on the transfer from my 2D domain into my pit and pipe network. The pits use a depth-discharge inlet curve. The model is direct rainfall and has a 0.5m grid cell size. The problem is that the depth at the pit and and the flow that should be entering the network from the curves does not match what is in the pipe directly downstream. Whats going on here? A: The solution here was that there was a "Pit Default Road Crossfall == 0.1" command in the .ecf The command Pit Default Road Crossfall increases the depth at Q pits based on the crossfall slope of the road cross-section. This approach aims to account for changes in ground elevation that occur at a finer scale than the 2D cell resolution. TUFLOW calculates the water depth that is used by the Pit Inlet Database using an adjacent side triangle depth approach, instead of the actual cell flow depth. Use of this command can improve the ability to capture water from 2D cells into pits feeding the pipe network. Especially for larger cell sizes, the shallow depth that can occur in the cell can be unrepresentative of the depth at the entrance to the pit, therefore restricting the amount of flow entering the pit. The larger depth using an equivalent triangle will push more water into the pit providing a more realistic representation of the pit’s capture. Below is a specific example on how the crossfall depth is calculated. The maximum depth reported at the pit channel is 0.009m. This results in a flow of 0.0054 using the curve. However, the flow reported in pipe downstream is 0.0017. This 0.009m depth is across the whole 0.5m cell. This results in a vertical area of 0.0045. Refer to the attached figure Now, we apply the crossfall factor. Its set to 0.1, which is a rise/run ratio of 1:10. The area stays the same and this results in a depth of 0.03 This crossfall depth results in a flow of 0.017 using the curves. This matches what is reported in the model csv and eof files.
Question: I am receiving different opinions about the flow transfer rate regarding flow from the 2D terrain to a 1D subsurface element. Group 1 says that flow is transferred from 2D terrain to 1D catch pit using the weir equation. Group 2 says that the user can enter the capture rate using a depth (m) to hydraulic capture (m^3/s) chart. All flow will be tranferred from the 2D terrain to the 1D catch pit according to the parameters of the chart. Which of these two groups is correct? How does TUFLOW transfer flow from 2D to 1D? Answer: In TUFLOW a pit channel is designed to convey water to/from a 2D overland domain to a 1D pipe network. There are multiple options available for calculating flows, these are: Depth-discharge curve ("Q" type pit)Weir flow ("W" type pit)Rectangular culvert ("R" type pit)Circular culvert ("C" type pit, this one is rarely used)For more information on setting these up please see the Chapter in the TUFLOW manual on Pits and Pit Channels. Regards TUFLOW Support Team