Subsurface Drainage:Subsurface Drainage
The SUPERLINK (Ji, 1998) model has been included in GSSHA to simulate subsurface drainage networks. The SUPERLINK model can be used to simulate urban subsurface drainage systems and agricultural tile drains. Networks can have both tile drains and surface inlets. Features include multiple networks, looped networks, discharge back on the overland and to channels. Superlink is implemented in GSSHA versions 5.1 and higher, and supported by WMS versions 8.3 and higher. The SUPERLINK method and its implementation is described in detail in the following document: SUPERLINK TN.
To use Superlink include the STORM_SEWER card with the name of the SUPERLINK pipe network file. The SUPERLINK pipe network file, .spn file, describes the SUPERLINK network, including the pipe network, the connectivity of the network, and physical attributes of drains, pipes, etc. The format of this file is very similar the channel input file, .cif file, used to described the stream network. When simulating tile drains, the connectivity between the tile network and the groundwater modeling grid is specified with the GRID_PIPE card, which is used to define the grid pipe file, .gpi file. This file format is very similar to the grid stream file, .gst file, used to describe the stream network connectivity to the overland flow grid. A SUPERLINK network consists of a two level description of the network. The network and its connectivity are described with junctions and superlinks. Junctions can discharge to streams or to the overland flow plane. A superlink can contain individual pipes connected with nodes. These inter-superlink attributes can be used to describe changes in the pipe properties, or just to add nodes for computational purposes. Superlink is sensitive to node spacing, so it is important to space nodes properly. Users should be careful to place the first computational node code to the junction. As an option to the definition of every computational node, the user can let GSSHA assigned the individual nodes for computational purposes, using the SUPERLINK_C_OPT card. Inlet drains can be placed at both junctions and nodes. Inlets can be allowed to discharge back to the overland flow plane during pipe surcharge periods by using the HIGH_HEAD_RELEASE card in the project file.
SUPERLINK is a fully dynamic, pressurized pipe routing package, and as such requires a properly spaced node network and may be computationally expensive. SUPERLINK is probably best applied for flood storm drainage systems where hydraulic routing is important. In cases where the routing is relatively fast compared to the pipe inflow, such as with tile drains, a simpler link/node method may be appropriate for use. GSSHA includes a simple link/node subsurface routing model that can be used in lieu of, or in addition to, a SUPERLINK network. The inputs for the link/node method are the same as for SUPERLINK, except the card STORM_DRAIN is used in lieu of STORM_SEWER, and DRAIN_GRID_PIPE is used in lieu of GRID_PIPE. Output from every SUPERNODE can be obtained by using the DRAIN_OUTPUT card with an output file name specified. Flows along pipes are accumulated along the drains and inlets and accumulated at each SUPERNODE. A drainage network can be specified with just junction nodes (SUPERNODES) without any interior nodes because there are no computations along the pipes. For this scheme to work, SUPERNODE numbers must increase in the downstream direction and the system cannot fork in the downstream direction. SUPERLINKS and drain networks can be mixed. The networks are separate and the cards described above are used to define the two networks. The drainage network can empty into the SUPERLINK but the SUPERLINK cannot flow into a drainage network. To specify a drain flows into a SUPERLINK node, the outlet type for the drain should be type 666 and the input should be the SUPERNODE number. See the SUPERLINK manual for the details on building the input files.
Pipes in the network are made tiles by defining the hydraulic conductivity of the pipe as anything greater than zero. Flow into the drains is as described by Cooke et al., (2001). Flow into the tile follows the methods used in DRAINMOD (Skaggs, 1980) when using the SUPERLINK_DRAINMOD card in the project file. Tile drains only impact the system when used with the WATER_TABLE card, as described in the section on groundwater simulation using GSSHA. Typically, tile drains are used during simulations of the free water surface, GW_SIMULATION, as described in the groundwater section.
The inputs required to run GSSHA using the Superlink model are described in the following document: SUBSURFACE DRAINAGE REPORT. The inputs required to build a Superlink-based GSSHA model can be specified using the WMS interface.
For more information about defining subsurface drainage information using WMS, visit the WMS Subsurface Drainage help page.
- Cooke, R. A., Badiger, S., Garcia, A.M. 2001. Drainage equations for random and irregular systems, Agr. Water Manage. 48, 207-224.
- Skaggs, R.W. 1980. DRAINMOD Reference Report - Methods for design and evaluation of drainage-water management systems for soils with high water tables. USDA SCS, South National Technical Center, Texas.
- Ji, Z., 1998. General hydrodynamic model for sewer/channel network systems. J. Hydrualic Eng., 124, 307-315.
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