Floodplain delineation with Free and Open Source Software ICUD/PDF... · 2 Floodplain delineation...

12th International Conference on Urban Drainage, Porto Alegre/Brazil, 11-16 September 2011

Pina et al. 1

Floodplain delineation with Free and Open Source Software

R. D. Pina1*, N. E. Simões2, 4, J. A. Sá Marques2 and J. O. Sousa3

1 AC, Águas de Coimbra, E.E.M., Rua da Alegria nº 111, 3000 – 018 Coimbra, Portugal

2 Department of Civil Engineering, University of Coimbra, Rua Luís Reis Santos, 3030-788 Coimbra, Portugal.

3 Department of Civil Engineering, Coimbra Institute of Engineering, Rua Pedro Nunes - Quinta da Nora, 3030-199 Coimbra, Portugal

4 Department of Civil and Environmental Engineering, Imperial College London, Skempton Building, South Kensington Campus, London, SW7 2AZ, United Kingdom

*Corresponding author, e-mail [email protected] ABSTRACT inp.PINS is an application developed to automatically link Geographical Information Systems (GIS) and the Storm Water Management Model (SWMM). By using the complex functions available, GIS is extremely useful in characterizing the base input model, and it is also a powerful tool in the archive, access, manipulation and visualization of SWMM inputs and results. With inp.PINS, a methodology based on free and open source software (FOSS) is presented in this paper for the delineation of flood risk maps. The performance of this methodology is illustrated with the results obtained for a study developed in Santa Comba Dão city, Portugal. KEYWORDS Free and Open Source Software; Geographical Information Systems; integration; interoperability; MapWindow; Storm Water Management Model INTRODUCTION According to the Free Software Foundation, free and open source software (FOSS) is a matter of the users' freedom to run, copy, distribute, study, change and improve the software. The development of FOSS is similar to the work of the scientific community, whose results are published in order to help in the development of new knowledge and obtain recognition for the quality of the research carried out. “It is a gift culture, just like developing FOSS, where the basics are taken care of and social status is gained by giving things away, rather than accumulating” (Harvey and Han, 2002). This FOSS freedom allows a fast development, expands the market and supports the rising of new companies to develop new applications, provide technical assistance, teaching, etc. This FOSS movement provides a useful alternative to the closed sources methods and the importance of this movement is demonstrated with FOSS project hosting platforms: nowadays Sourceforge has 2.7 million developers working on 260 000 projects and provides more than 2 million software downloads per day; Codeplex, a more recent project hosted by Microsoft, saw the number of downloads increased nearly 100 % in the last year. FOSS projects are an ongoing process review and its success is based in a continuous Darwinian process of natural selection in the FOSS ecosystem, ensuring rapid development and innovation. The starters of a project are the reviewers at the outset and in most cases retain that position for as long as they maintain an interest in the project (Harvey and Han, 2002).


2 Floodplain delineation with Free and Open Source Software

FOSS examples can be found in areas like GIS and hydroinformatics. FOSS for Geospatial (FOSS4G) have been promoted by the Open Source Spatial Foundation (OSGeo) whose mission is to support the collaborative development of open source geospatial software, and promote its widespread use. This Foundation takes an important role in promoting FOSS4G and ensures high quality projects that are becoming very important, such as GRASS and QuantumGIS. EPANET and SWMM are two examples of public domain software, developed by the United States Environmental Protection Agency, which became very important and well known in the hydroinformatics field. Besides the fast development achieved by the community and the great amount of testers, this way of working also takes care of social issues by providing advanced modelling capabilities for everyone. Nowadays, an important issue is to work with all this software together and take advantage of each one’s capabilities. The integration of various software and the interoperability allow an easy exchange of data taking advantage from each software functions. FOSS projects are usually based on standards for enabling interoperability between different applications from different developers. Users usually find difficult to transform data coming from GIS to SWMM and vice-versa. The need of an interface that couples SWMM and GIS is obvious: the use of these two software packages separately means losing capabilities, or even data, leads to inconsistencies and doubles the work. This field has been explored by proprietary software, although the availability of such an instrument as FOSS can be useful to spread the use of this tool, allowing the community to run, copy, distribute, study, change and improve the software, in order to obtain the best from the two environments. Water management agencies also embraced the use of FOSS, since various components can be linked without the need to contract the original developers of such software components. With the current trend of developing integrated models of hydraulics, hydrology and environmental systems, the development of such platforms becomes even more desirable. (Verwey, 2005). This paper presents inp.PINS, an application developed to automatically link Geographical Information Systems (GIS) and the Storm Water Management Model (SWMM). GIS is a powerful tool in the archive, access, manipulation and visualization of SWMM inputs and results. An methodology based on FOSS (link between GIS and SWMM) is presented for the delineation of flood risk maps. The performance of this methodology is illustrated with the results obtained for a study developed in Santa Comba Dão city, Portugal. GIS AND SWMM GIS is a general term related to the use of geographically referenced information and provides a common platform in which people and data interact. GIS offer a viable framework for the simulation modelling integration since the modelling of a system includes space, together with time, as a common denominator (Cesur 2007). There are GIS projects available as FOSS, known as Free and Open Source Software for Geospatial (FOSS4G), for example: Grass, QuantumGIS or Mapwindow. SWMM is a dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas (Rossman, 2009). Developed by the United States Environmental Protection Agency, SWMM is a public domain software, widely used throughout the world for planning, analysis and design related to stormwater runoff, combined sewers, sanitary sewers, and other drainage systems in urban areas, with many applications in non-urban areas as well. Aims of the integration between GIS and SWMM GIS have been recognized as a powerful tool to integrate and analyse data from various sources in the context of comprehensive floodplain management (Correia et al. 1999).


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inp.PINS was developed to link GIS and SWMM by taking advantage of GIS and its complex functions, to better characterize the model and to better analyse modelling results. As shown in Figure 1, inp.PINS can be used to generate SWMM input file (.inp) with the information gathered from GIS files and, after the SWMM analysis, inp.PINS builds shape files (.shp) with the data collected from the SWMM results file (.rpt).

Figure 1. inp.PINS working diagram.

The link between SWMM and GIS is advantageous not only to create models and visualize the results, but also during the calibration and validation processes. With this methodology, new scenarios and model developments are easily explored and analysed. Through the use of inp.PINS, additional archive, access, manipulation and visualization capabilities for SWMM modelling are achieved. The integration of the SWMM data in the GIS environment offers several possibilities: spatial analysis, topology tools, geostatistics, satellite and aerial photograph image analysis. inp.PINS inp.PINS is designed to link SWMM visual objects, and their characterization, with GIS. Based on object oriented approach, inp.PINS works on a flexible way, since the pointers that link object characteristics are defined by the user. inp.PINS was developed under VB.NET, using MapWinGIS ActiveX control, and it is organized in three main modules:

i. inpMaker – to create *.inp files based on GIS data; ii. inpFlood – to build *.shp files with results from SWMM combined with Digital

Elevation Model (DEM); iii. inpTools – functions to help managing GIS data: create nodes from links, find extreme

link nodes, subcatchments connections. inpMaker and inpFlood are two independent MDI Child forms and inpTools is available in the main menu of inp.PINS (Figure 2). Common controls (File, View, Help) and status bar completes the Graphical User Interface for an easy use and XML project files can be saved and opened with all configuration data.

Figure 2. inp.Maker module (left) and inp.Flood interface (right).



inpMaker

inpMaker has a TreeView on the left with all the SWMM objects and a property grid on the right to define the link shape file pointers. The columns fields of a selected shape file are linked to each object characteristic. All the necessary data to create an *.inp file can be edited by the user, such as default values and options or title or notes that can be inserted in the bottom text box. inpMaker has the ability to generate cross sections (XS) from a DEM grid for channel links, defined as IRREGULAR shape conduits in SWMM. The location of the XS can be defined by the user with a polyline shape file, otherwise inpMaker builds the XS at the midpoint and perpendicular to a line defined by their extreme vertices. Overbanks can also be defined with a polyline shape file that intersects the XS shapes.

inpFlood

inpFlood analyses the SWMM *.rpt data file combined with the cross section data from the *.inp file (if exists) and/or DEM grid to generate flood plains. This procedure is illustrated in Figure 3, and starts by reading the nodes maximum water depths from *.rpt data file. Then, the conduits are divided in sections displaced with a distance "di". For each of these sections, water depth is interpolated from the upstream node to the downstream node, and analysis of the conduit geometric XS (for IRREGULAR conduits shapes) and/or DEM grid at that XS (for ALL conduits shapes if a DEM grid is given) takes place to define the floodplain limits. The geometric XS is placed along the conduit for each "di" point and its elevation is changed linearly by the conduit upstream and downstream invert level. If these two options are selected inpFlood will give the smallest flood plain between cross section and DEM result. Only conduits are analysed, no matter their shape – DEM analysis will take place to define flood plains for non IRREGULAR shape conduit.

Figure 3. inpFlood algorithm.


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CASE STUDY After several flood events and according to the Directive 2007/60/EC of the European Parliament and of the Council of 23 October 2007, the authors worked with the Santa Comba Dão City Council in developing flood risk maps and flood management guidelines to support urban planning. Ribeira das Hortas Catchment Ribeira das Hortas Catchment is located in Santa Comba Dão Municipality, Portugal, and discharges to Dão River. Santa Comba Dão city is in the downstream part of the catchment and the River Ribeira das Hortas crosses the downtown area (Figure 4).

Figure 4. Ribeira das Hortas Catchment.

Ribeira das Hortas is a 14 km2 catchment that discharges to Dão River. It has a rural area at the upper zone and an urbanized one downstream, with high slopes (Table 1).

Table 1. Ribeira das Hortas characterization. Area 13.96 km2 Perimeter 25.5km Maximum Elevation 348 m Minimum Elevation 122 m Average slope 5.7% % impervious area 40% Time of concentration (Kirpich) 110 min

Methodology The FOOS4G used was QuantumGIS and MapWindow with several plug-ins: TauDEM, developed by David Tarboton (Utah State University) and GRASS, initially developed by US Army Corp of Engineers and now a project of the OSGeo. The automatic link between GIS and SWMM was provided by inp.PINS. Figure 5 shows the DEM with the stream network designed and the slope map, generated by GIS, necessary to run the SWMM model.



Figure 5. Digital elevation model and network drainage system at the left and slope

analysis at the right. The initial data needed to build the SWMM model are the physical catchment characteristics – area, length, width, slope, pervious areas, and the hydrological and hydraulic catchment characteristics – Gauckler-Manning-Strickler coefficients, depression storage and infiltration parameters. All this data was calculated with the help of GIS. QuantumGIS was used to build the digital elevation model and perform the slope analysis, based on the topographic information provided by the city council, and for converting aerial photos in binary image for impervious areas calculations. After that, TauDEM was used for catchment delineation and drainage system design. GRASS was used as a QuantumGIS plug-in for geostatistics applied to each sub-catchment. Typical Gauckler-Manning-Strickler coefficients were used for the land type and use observed and depression storage was characterized according to Butler and Davis, 2004:

( )s

k=d

where, k – coefficient depending on the surface type (0.07 for impervious surfaces and 0.28 for

pervious surfaces) (mm) s – ground slope.

Horton infiltration parameters are presented in Table 2 (Butler and Davis, 2004).

Table 2. Horton infiltration parametes. Maximum infiltration rate (mm/h) 75 Minimum infiltration rate (mm/h) 3 Decay constant (1/h) 2

The SWMM model was calibrated and validated with knowledge from similar studies and by comparing the results with data from flood registered events.


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The GIS was integrated with the SWMM model taking advantage of the inp.PINS capabilities. All the characterization process was developed in the GIS environment, and the results were used to build the *.inp file. After the SWWM analysis, inp.PINS was used again to integrate modelling results into the GIS. Flood plain delineation results The flood plains obtained by the methodology presented (Figure 6) are in accordance with the data collected from the flood events registered: for 5 years return period no flood problems occur, but for more than 10 year return period important buildings are affected, such as the city council and the fire-station. Therefore, flood management guide lines were developed and a solution to mitigate flood problems was proposed based on the Sustainable Urban Drainage Systems concept.

Figure 6. Flood plain delineation result.

DISCUSSION AND CONCLUSIONS The project presented here was developed according to the EU Directive 2007/60/EC. Taking advantage of FOSS, it establishes a methodology based on the ‘best available technologies’



not entailing excessive costs and ‘best practice’ were taken care for flood management guide lines development and for the flood mitigation solution proposed. The methodology presented, which is based on inp.PINS, reveals to be an efficient way to integrate GIS and SWMM. The interoperability achieved is very effective for the analysis required, since the process leads to a better characterization of the model and better analysis of the modelling results, taking advantage of the GIS and SWMM capabilities at the same time. FOSS have advantages the advantage of allowing the development of tools adapted to the user’s needs, in addition to reduced costs (or even total exemption) for the acquisition and maintenance of licenses, as illustrated by the application inp.PINS. Developed with the aim of integrating GIS with SWMM, inp.PINS is presented at https://sites.google.com/site/inppins/ and is available on the MapWindow official website (http://www.mapwindow.org/). inp.PINS is a tool for all SWMM users, who can now afford from all GIS advantages with a FOSS. The open source community is able to improve the capabilities, and also to make it even more flexible. inp.PINS is now available for interoperability between SWMM and GIS, but further work can extend this methodology to EPANET, depending on the users expectation and suggestions. The project is now driven by the community needs (in the first six month of the project the software was downloaded more than 300 times and the help web page was visited more than 400 times, by almost 50 countries from all continents). The main limitation of this project is related to the developments of EPA software, whose standards must be well defined. SWMM and EPANET can also be improved by the FOSS community. Standards must be defined for the guaranteed success in the hands of the community who will help on its developments and also on testing it for growing up in an efficient and fast way. Standards and shift developments will provide developers the means to do what they have wanted and the desire to do even more (Kopp, 1996). ACKNOWLEDGEMENTS Nuno Simões acknowledges the financial support from the Fundação para a Ciência e Tecnologia - Ministério para a Ciência, Tecnologia e Ensino Superior, Portugal [SFRH/BD/37797/2007]. REFERENCES A. Verwey: Hydroinformatics Support to Flood Forecasting and Flood Management. Proceedings of “The

Fourth .Inter-Celtic Colloquium on Hydrology and Management Water Resources”, Guimarães, Portugal, 2005.

D. Butler, J. David: Urban drainage. ISBN 0-203-14969-6, 2º edition, 2004, Taylor & Francis. D. Cesur: GIS as an information technology framework for water modeling. Journal of Hydroinformatics, 9.2,

123–134, 2007. F. Correia, M. Saraiva, F. Silva and I. Ramos: Floodplain management in urban developing areas. Part II. GIS-

based flood analysis and urban growth modelling. Water Resources Management, 13, 23-37, 1999. H. Harvey, D. Han:The relevance of Open Source to hydroinformatics. Journal of Hydroinformatics, 04.4, 219-

234, 2002. L. A. Rossman: Storm water management model - user’s manual. Version 5.0, 2009, U.S. Environmental

Protection Agency, Water Supply and Water Resources Division, Cincinnati, OH 45268. MapWindow Open Source Team: MapWinGIS reference manual. 2007, URL: www.mapwindow.org. S. Kopp: Linking GIS and hydrological models: where we have been, where we are going? Proceedings of

“HydroGIS 96: Application of Geographic Information Systems in Hydrology and Water Resources Management” Vienna, Austria, 1996.

Floodplain delineation with Free and Open Source Software ICUD/PDF... · 2 Floodplain delineation...

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