Development of Application Tools for Burying and Sizing of Subsurface Drain Tiles

Anamelechi Falasy^* and Richard Cooke
^*Correspondence: Anamelechi Falasy, Department of Agricultural and Biological Engineering, University of Illinois, Urbana-Champaign, Illinois, USA, Email:

Keywords

Tile burying systems • Pipe sizing distributions • Elevation depths • Pipe estimations • Drainage coefficients • Spreadsheet exports

Introduction

Agricultural subsurface drainage systems are extensively implemented in agricultural fields to eliminate surplus water, transforming poorly drained soils into fertile cropland, and ultimately bolstering agricultural profitability. As a result, vast swathes of the Midwestern US have been converted into highly productive agricultural areas [1-5]. Subsurface drainage entails the installation of a network of underground pipes (commonly referred to as tiles) positioned approximately 1–2 meters beneath the soil surface. These pipes facilitate the gravitational drainage of water, directing it towards a primary drain or surface water body. Through engineering calculations, the required tile size for the drainage system is determined based on the anticipated volume of water to be conveyed. By regulating the water table at a depth of 1–2 meters below the ground surface, drain tiles promote the development of robust crop root systems and mitigate the adverse effects of excessive water on crop growth, all while operating within the designated capacity of the drainage system [6,7].

An advanced knowledge of drain materials and installation techniques is important for accurate depth placement and sizing of drain tiles in subsurface drainage design, to achieve sustainable development of both irrigated and rainfed agriculture [8,9]. A variety of guidelines and software applications have been developed for laying out, burying (setting depths and slopes) and sizing drain tiles in subsurface drainage systems. Currently, drainage contractors typically use proprietary design packages. Three software packages are discussed below:

When paired with Trimble's WM-Drain^® solution, the Trimble WM-Subsurface™ design software constitutes a comprehensive toolkit encompassing surveying, analysis, design, installation, and mapping for both surface and subsurface drainage. This integrated solution guarantees the optimal placement of 3D drains, resulting in increased crop yields through the management of ponding, enhancement of root depth, extension of planting seasons, and reduction of nutrient loss. The Trimble WM-Subsurface Farm Drainage Software™ emphasizes the ideal positioning of tile and surface drains in surface and sub-surface drainage water management endeavors, enhancing field drainage and boosting crop yields [10]. Key functionalities include the software's ability to “tie laterals to mains, create parallel lateral spacings, and clip drainage lines”, the verification of the pipe network's successful drainage to the main outlet using the drainage line creation tool. The WM-Drain solution further employs an automatic pipe sizing tool to calculate recommended pipe sizes and estimate total costs and materials, facilitating the production of optimal drainage designs while reducing overall expenses [11]. AGPS-Pipe Pro™ facilitates the laying of drainage pipe or tile [12]. This program captures the topography of a tile line and utilizes this information to calculate the elevation and grade of the pipe, controlling the plow blade during the laying process. TileLogic MC™ primarily aids in drainage installation, field survey, and mapping. Additionally, it is equipped to perform virtual burying and sizing calculations for extensive projects with multiple drainage networks [13].

Other software packages that have been developed and used for research and educational purposes include DrainCAD [14], LANDRAIN [15], MACDRAIN [16], and SUBDRAIN [17]. These software packages predate Microsoft WINDOWS and/or the widespread use of Geographic Information Systems (GIS) for drainage design.

Each software tool offers specific features and functionalities that cater to different design requirements and project scales. When selecting a software tool, it is essential to consider project specific requirements, the level of complexity needed, the software's compatibility with the existing design workflows, and the expertise level needed. These software programs offer drainage design modules that incorporate hydraulic calculations, allowing engineers and designers alike to determine the appropriate elevation depth for drain tiles and generate accurate pipe sizing, slope determination, and overall system layout based on design criteria and site-specific conditions. The complexity and sophistication of these tools has limited their widespread adoption due to the level of expertise required. Moreso, although many other researchers and engineers have developed low-cost techniques for subsurface drainage design and installation, their methods still require a high level of expertise to utilize.

A recent development in subsurface drainage theory that could potentially lead to the development of optimized drainage systems is the disaggregation of what was formally called the drainage coefficient into three coefficients, the Kirkham Coefficient (KC), the Drainage (or Design) Intensity (DI), and the Drainage Coefficient (DC) [4]. Drainage systems can be optimized by uncoupling the flowrate used for determining lateral depth, spacing, and sizing (That is: DI); and the flowrate used for the sizing of sub-mains and mains (That is: DC). Subsurface drainage systems are typically designed with the DI and the DC set to the same value. Hither to Skaggs RW, et al. [18] the terms have been used interchangeably to represent the same drainage rate [19-21]. The DI represents the steady state drainage rate (cm/d) at which water can flow through the soil profile to the drain when the water table, positioned midway between parallel drains, aligns with the surface. Conversely, the DC quantifies the hydraulic capacity of the system, indicating the maximum rate (cm/d) at which the outlet can remove water from the site through the drains. Together, these two coefficients (DI and DC) delineate crucial subsurface drainage rates that delineate the hydraulics of the system at a fundamental level. They are instrumental in characterizing various processes required within the system, as illustrated in Figure 1. Skaggs RW [4] suggests that for an optimal system performance the values should be uncoupled, with the DC being at least as large as the DI. This implies that the Drainage Coefficient (DC) should be greater than or equal to the Drainage Intensity (DI) to prevent any decrease in drainage rates and effectiveness. In most existing software packages DC is the same DI. One notable exception is Landrain in which it is possible to have a DC that exceeds DI by specifying an “overdesign” factor for mains [16,22,23] (Figure 1).

Figure 2 provides a schematic overview of the drainage design process, spanning from initial planning to installation. The outlined steps include: 1) gathering background information on soils, topography, and crops, 2) evaluating the need for drainage, 3) assessing the availability of a suitable outlet, 4) specifying design parameters like intensity, depth, and spacing, 5) planning the layout for laterals and mains, 6) structuring pipes into a topologically sound network, and 7) determining appropriate depths, grades, and sizes for drainage pipes. To streamline this process, we've developed GIS-based tools known collectively as the "Illini Drainage Tools" (IDTs). These tools are divided into three groups, each serving a specific purpose: the first aids in layout and digitization, the second focuses on network development, and the third is dedicated to pipe installation, including grade and depth determination (burying), as well as sizing. This paper specifically introduces the final set of tools, crucial in simplifying the burying and sizing processes of drainage networks (Figure 2).

We have developed a set of public-domain QGIS-based tools for burying and sizing tile network the eliminates the drudgery of manually calculating pipe sizes based on terrain, depth, and drainage coefficients, distributions in subsurface drainage systems. The goal was to provide a no-cost, user-friendly toolkit to bury and size drainage pipes in which DC can be specified by pipe function, pipe size, or specified for each individual pipe. Additionally, the tools offer a cost estimate for the sized pipes and provide output in several formats suitable for input into drain installation machines. In this paper, we showcase the capabilities of these new tools, and use them to bury and size a subsurface drainage system for a field at the South Farm of the University of Illinois in Urbana-Champaign.

Materials and Methods

Design and development of tools

Geographic Information Systems (GIS) have proven to be effective tools in the design of subsurface drainage systems, as evidenced by various studies [24-29]. The integration of GIS enhances the precision of drainage pipe design by offering a visual representation of the terrain and supporting data-driven decision-making processes [30,31]. This includes activities such as monitoring channel flows, mapping stream networks, and creating contour lines. The Quantum Geographical Information System (QGIS), chosen as the open-source GIS software platform for these processes and tool utilization [32], allows for the development of new plugins in the Python 3.10 programming language (http://python.org). QGIS provides online support through forums, tutorials, and documentations (http://www.qgis.org). Using these plugins or extensions, QGIS enhances its functionalities and introduces new features without altering the main software program, thus expanding its capabilities. QGIS is publicly available, widely taught in scientific institutions, and its source code is freely accessible. It has a large community of developers and is compatible with various operating systems, including Mac OS X, Linux, Unix, and Microsoft Windows. Many applied scientists continue to leverage the QGIS platform to develop plugins tailored to their specific fields of interest. For instance, the platform was utilized to create a set of QGIS-based tools designed to facilitate the layout of drainage systems [33].

Currently, there are no free and easy-to-use compact GIS toolkit with built-in functionality in the QGIS processing toolbox or elsewhere, that uses an input file of a topologically sound and unidirectional vector line layer to bury and size subsurface drainage network systems, and as well as provide possible costs associated with sizing, using different pipe materials, and requiring minimal level of GIS expertise. To address this gap, the following four tools have been developed, namely:

• Tile Burying System [J]: used to determine the elevation depths for burying the drain tile network
• Network Pipe Sizing [K]: used to determine the pipe sizes for respective tile segments in the network
• Sized Pipe Estimations [L]: used to estimate the prices of sized pipes in the network
• Tile Spread sheet ReadOut [M]: used for exporting attribute features to transferable formats

The construction of these new tools involved the utilization of Plugin Builder 3.2.1 [34] and Plugin Reloader 0.9.1 [35]. Qt Creator 5.0.2 [36] was employed for the development of the Graphical User Interface (GUI), while the associated functionality was implemented using Python 3.8 along with the QGIS3/Python standard libraries (gdal, math, numpy, datetime, and os). Comprehensive installation instructions and the source code for these tools are available at: github.com/FVW-Services/Illini-Drainage-Tools/blob/main/README.md

Application and testing

To assess the tools, we utilized a well-structured tile network for a field on the University of Illinois's South Farm (Figure 3). All the data layers essential for tool testing are available online and can be accessed through the Illinois Drainage Guide at https://publish.illinois.edu/illinoisdrainageguide/.

Results and Discussion

Implementation results from tools

These four tools, featured in this paper, represent the final options in the dropdown menu of the installed IDTs package suite in QGIS, which can be obtained from the official QGIS plugin repository. Previous discussions have encompassed the functionalities and capabilities of the initial nine tools within the IDTs [33]. The final set of tools introduced in this paper is designed for independent use. They are applicable to any vector line layer representing network distribution in QGIS, provided it contains the following essential fields: (a) a sequence determining the burial order in the drainage network, (b) initial elevation points for all segments, (c) terminal elevation points for all segments, (d) the distance between the elevation endpoints, (e) a unique segment ID assigned in ascending order, (f) a segment ID indicating link connections between segments, (g) a top-down tile ordering for the segments, and (h) cumulative flow lengths for all adjoining segments. Once these fields are present and applied to the first two tools, as outlined in the paper, the remaining two tools seamlessly utilize their outputs and inputs, with minimal additional requirements from the user.

Tile burying system

The application tool, Tile Burying System [TBS], with interface in Figure 4, was developed to determine the minimum size of each section of the drainage main that can carry the upstream design flow in the system. This tool uses the output from the Network Flow Lengths [I] [33] tool as the input file and is a follow-up tool from the IDTs plugin. However, any line layer with the required input fields, shown in Figure 4, can be used. The tool has minimal input requirements; a line layer of tile network with its routing reference fields, and the specification of maximum and minimum required buried depths and slopes. There is an option for burying each pipe with a uniform slope (underlined in red in Figure 4). The default option is for a pipe to have a range of slopes, mirroring the topography of the soil surface. The GUI for this and all the other tools in the IDTs is comprised of a main window with two different input sections (A, B) and a usage information window (C). Section A contains the input parameters that are essential for the tools to work, while Section B defines the output data files resulting from running the tools (Figure 4).

Network pipe sizing

The application tool, Network Pipe Sizing uses the output from the TBS tool as the input file to determine the proper sizing in the entire distribution of tile network, upstream to downstream of the subsurface drainage system. The tool mainly relies on the values of the Tile Order, Cumulative Flow Lengths, Burying Slope and the Manning’s roughness, n for the selected material type for determining the pipe size in each line segment. Its input requirements include a vector line layer of tile network with its routing reference fields, the burying slope, the specification of drain spacing, the type of tile material and the drainage intensity. A significant part of the tool is highlighted in section B, for advanced parameter setting options for specifying the tile spacing and for specifying how the Drainage Coefficients (DCs) used by the tool are generated. These advanced options provide flexibility for expert designers and experienced contractors. The user interface for this tool is shown in Figure 5.

The tool offers two flexible options for specifying the tile spacing (a) single: for assigning a uniform spacing value for the entire tile network, and (b) multiple: for assigning different spacing values for different segments of the tile network (Figure 6). In addition, three options are provided for generating and using DC values (Figure 7). The fir st option is the DC values been determined and assigned internally by the tool, using the input parameters. This is the default option. The second option is the DC values for each individual tile segment in the network, assigned based on their respective orders. This involves specifying the DC values, starting from the lowest order to the highest and separating the values with a comma. The third option is the DC values selected from a newly created field, “SELF_DCF”, in the vector layer containing assigned drainage coefficients for each individual tile segment in the network line.

Figures 6 and 7 show a GUI snippet for the two advanced options for specifying the tile spacing and for generating and using DC values. Both options illustrated in Figure 6 are tedious and require advanced knowledge (Figures 5-7).

Sized pipe estimations

The tool, Sized Pipe Estimations with interface shown in Figure 8 was developed for generating possible prices for the different pipe sizes determined using their frequencies and total lengths. The tool also renders the vector line layer into different sized pipes and then estimates the cost based on the values provided by the user in the special CSV file called “prize_table”, as shown in Figure 9. The estimations are done simultaneously for all four (4) types of pipe materials featured in the Network Pipe Sizing tool, namely: Single-Wall, Smooth-Wall, Clay-Wall, and Concrete-Wall. These estimations give insight on the possible economic implications of using different pipe material types. This tool is sequel to the Network Pipe Sizing tool since it uses its output as input layer (Figure 8).

Figure 9 provides a visual representation of the "prize_table" screen display. The default pricing for various pipe types and sizes is set at $1. This file provides a structured format for users to input and customize pricing information, ensuring accurate and tailored estimations based on specific pipe types and sizes. Users can modify the values in the CSV file to reflect the prevailing costs and currency of their respective locations, enhancing the adaptability and relevance of the pricing estimates. The link for downloading this file is provided in the C (usage information) section, in Figure 8 (Figure 9).

Tile spreadsheet readout

The tool, Tile Spreadsheet ReadOut, with interface shown in Figure 10 was developed for splitting the tile network distribution using its unique segment ID and then exporting into separate spreadsheet files, with each corresponding to a tile segment in the network. This tool has the capacity to export the attribute table of any type of vector shapefiles into comma delimited (csv), Excel (xlsx) or Text (txt) files. This format allows for the seamless transfer of this information to a drain installation machine (Figure 10).

Experimental testing results from tools

Once executed, the four tools produce their respective output layers. The primary source codes responsible for the execution of these tools are found in the Python files, namely:

• py,
• py,
• py, and
• py.

These files are responsible for generating and managing the Graphical User Interfaces (GUIs) on the front end, while the interactive GUIs in QT designer mode showcase the function keys of the tools. Test data, along with instructions for utilizing these tools—including a step-by-step PowerPoint file and a video guide—are available in the Illinois Drainage Guide at publish.illinois.edu/illinoisdrainageguide/illini-drainage-tools.

The successful testing of this toolset, as demonstrated in the application example depicted in Figure 3, suggests its high efficiency in swiftly accomplishing objectives with simple "one-click" actions, particularly in the processes of burying and sizing drainage networks. Additionally, the tools facilitate the rendering, estimation, and exportation of costs for various pipe material types and sizes. Upon running all four tools consecutively, the outcome comprises exportable outputs detailing buried elevation depths, nominal pipe sizes, and price estimations for the entire network distribution, as outlined below:

In Figure 11, a representative log report screen is displayed following the execution of the TBS tool. This screen provides information on the success of the routine, the duration of execution, and details such as the name and location of any generated output files. Comparable reports are generated for each of the four tools (Figure 11).

Figures 12 and 13 depict attribute tables and corresponding screen displays that showcase diverse outputs resulting from the execution of the Tile Burying System [TBS] tool. In Figure 12, a comparison is drawn regarding elevation depth values across different field terrains, highlighting the distinction between burying with a constant slope and without. When buried with a constant slope, the tile layout adopts a relatively straight line, whereas it conforms to the terrain's shape when no constant slope is applied, as depicted in Figure 12. Additionally, the numbering in Figure 13 illustrates that each line segment is buried before any upstream segments of it (Figures 12 and 13).

In Figure 14, the screen display following the execution of the Network Pipe Sizing tool is presented. The symbology rendering visually represents the distribution of various pipe sizes within the network, progressing from upstream to downstream in ascending order. This ensures that each pipe segment is sized before any downstream segments of it. The output fields from the attribute table encompass the Drainage Coefficient (DC), system flow, and both actual and nominal pipe sizes (Figure 14).

Field-testing validation of tools

To assess the effectiveness of the recently implemented tools, we conducted a validation by comparing the outcomes from a proprietary software package with the results generated by the new tools. While the software is said to be DOS-based software was run on Windows using a DOS emulator (DOSBox). We further developed another Plugin in the QGIS platform to convert the output from the software into a shapefile so that it can be displayed in a GIS environment. This comparison specifically focuses on the burying slopes and estimated sizes of pipes, utilizing identical pipe installation parameters for a subsurface drainage layout system implemented at a field in Piatt County, Central Illinois, for which the layout was provided by a local drainage contractor. The resulting outputs are shown in Table 1 below.

In Table 1, both the existing software and the new tools show a consistent value for burying slopes with no apparent differences. In general, the actual and nominal pipe sizes generated by the new tools are sometimes a size smaller than the corresponding pipes generated by the existing software. These discrepancies are relatively small in magnitude. Across the dataset, instances arise where identical burying slopes yield differing actual and nominal pipe sizes between the two methods, suggesting a systematic difference in the design capabilities and strategies employed for subsurface drainage system design by the two systems.

Despite variations, both approaches maintain a degree of consistency in burying slope and pipe size distributions, hinting at shared underlying design principles or constraints. However, unique combinations of burying slopes and pipe sizes in each method imply adaptability to diverse drainage scenarios or specialized functionalities. While variations in burying slopes and pipe sizes may suggest optimal combinations for effective drainage, it's crucial to recognize the inherent variability between different subsurface drainage design software and a design contractor methodology. Each contractor's approach is influenced by factors like experience, field variability, and client preferences.

Figure 15 shows the variations in the estimated nominal pipe size recommendations in the outlet segment for the subsurface drainage layout design between the two methods: proprietary software package (in BLACK) and the implemented the new tools (in WHITE). Both methods provide the same value for burying slopes, however there is a noticeable difference in nominal pipe sizes between the existing software and the new tools (Table 1). The nominal pipe size provided by the new tools (12”) is smaller compared to that from the existing software (15”). Similarly, there exists a slight difference of 1.73 between the existing software and the new tools (Table 1). The actual pipe size generated by the new tools (11.15”) is smaller compared to that from the existing software (12.88”). These slight variations towards the system outlet suggest potential areas for optimization in drainage system design. This comparative visualization serves as a valuable reference, aiding in understanding the differences between the two methods and informing decision-making in drainage system implementation (Figure 15).

While acknowledging the capabilities of the proprietary software package in handling the burying and pipe sizing operations for the subsurface drainage system, the software system runs on an older version of operation system which may pose a challenge to a new designer. Moreover, it is apparent that the program lacks the flexibility offered by the newly introduced tools, as illustrated in Figure 5. The new tools present a notable advantage by enabling users to apply different drainage intensity values to various segments within the layout, whereas the proprietary software restricts users to applying a single value. Another noteworthy benefit of the new tools is their efficiency in performing burying and pipe sizing operations, accomplishing the tasks in less than 10 minutes. In contrast, the proprietary software requires over 2 hours for the same operations, depending on the complexity of the subsurface drainage system layout. This substantial time difference underscores the efficiency and speed gains achieved through the utilization of the new tools. Furthermore, the economic aspect is a key consideration. The new tools provide a more cost-effective determination of the pipe sizes, allowing for the use of smaller pipes compared to the larger diameter pipes recommended by the proprietary software. This not only contributes to potential cost savings in material but also reflects a more optimized approach to the sizing of pipes within the subsurface drainage system.

The four tools discussed in this paper, part of the Illini Drainage Tools (IDTs), represent the concluding phase of a three-step design process for drainage systems within the QGIS software platform. This final stage focuses on creating application tools to facilitate the burying and sizing of drainage networks, following the preceding two stages that involve drainage system layout design and the establishment of topologically sound, unidirectional flow tile networks [33].

When utilizing the Tile Burying System [J] and Network Pipe Sizing [J] tools, depicted in Figures 4 and 5, it is advisable to carefully define the input requirements to accurately reflect the topography of the field. This ensures the tools effectively bury and size the entire tile network distribution. Additionally, for users employing the advanced options in the Network Pipe Sizing [J] tool, adhering to the instructions provided in the information window is recommended.

The outcomes presented in this paper are confined to the results derived from burying and sizing drainage networks using input files generated with the IDTs. The output prices presented by the Sized Pipe Estimations tool provide estimates for the potential costs of sized pipes across four material types featured in the Network Pipe Sizing tool: Single-Wall, Smooth-Wall, Clay-Wall, and Concrete-Wall. While actual pipe prices may vary between vendors and states, these estimates offer valuable insights for planning and decision-making purposes.

The development of these tools has undergone numerous revisions and enhancements based on feedback from test users. This iterative development process remains ongoing, and we welcome input and ideas for further improving the tools. We also encourage users to test and apply these tools with data beyond the provided samples.

Conclusion

This suite of tools offers a straightforward and user-friendly method for burying and sizing drainage networks, utilizing a geometrically aligned and unidirectional vector line data file with cumulative flow length parameters. The case studies demonstrate the tools' effectiveness in successfully burying and sizing the entire tile network distribution. The outputs not only provide valuable insights for making informed cost-benefit decisions based on system recommendations but also offer a practical guide for designing subsurface drainage systems. This is particularly beneficial for farm owners and inexperienced contractors embarking on new drain installations, streamlining the otherwise intricate process of reaching economic conclusions using a GIS platform.

Author Contributions

Conceptualization, A.F. and R.C.; Methodology, A.F. and R.C; Software, A.F.; Visualization, A.F.; Validation, A.F. and R.C.; Formal Analysis, A.F. and R.C.; Investigation, A.F. and R.C.; Resources, A.F. and R.C.; Writing—original draft preparation, A.F.; Writing—review and editing, A.F. and R.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data to this communication can be found online at https://publish.illinois.edu/illinoisdrainageguide/illini-drainage-tools.

Supplementary Data

The “Prize_Table datasheet for inserting the pipe prices can found online at

https://drive.google.com/file/d/1CJ5yFAuIZeRE1vOX1FEWkeTbSHunxtId/view?usp=sharing.

Acknowledgments

We would like to thank the graduate students of ABE 459 (Drainage and Water Management) whose anonymous reviews and comments shed light on the routine performance and thus improved the quality of this communication.

Conflicts of Interest

The authors declare no conflict of interest.

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