Automated Design of Urban Wastewater Systems SUBMITTED BY

Automated Design of Urban Wastewater Systems SUBMITTED BY Kenneth Johnson Texas A&M University CVEN 689: Applications of GIS to Civil Engineering Instructor: Dr. Francisco Olivera May 9, 2005 Abstract The operation of today’s wastewater systems requires ongoing planning, maintenance, and management. Planning of these systems involves a thorough investigation of the intended use and site. It is common for surface water runoff to be separated from urban wastewater. The following investigation focuses on the design on new urban wastewater systems. The need for new pipelines arises as a city grows and the extension of sewer systems becomes increasingly important. Site investigation is then explored for economic and safety concerns. Movement of wastewater through a sewer system is preferably done by gravity forces. Optionally, lift stations are used whenever gravity forces can not be applied. These pumps or lift stations should be avoided when possible due to their relative expense and unreliability. The following project illustrates the automated process of extending a wastewater system. Land Use Cost Raster Methodology A cost raster based on the type of land use must be created firstly to point design pathways away from existing structures. The cost values associated with the land use remain low for allowable construction directions while much higher values are to be assigned to the existing buildings and roadways. Another cost raster is created based the slope of the terrain. As mentioned previously, gravity will provide the flow through the pipelines in most cases. Flow uphill consists of transporting wastewater opposite the slope of the terrain. Given a point of interest, where the pipeline will extend to, a correlation is made between the intended direction and slope direction. An equation is used for three possible cases of gravity flow given directions based on degrees. The figures below illustrate the process to achieve an allowable gravity flow raster. In the allowable gravity flow, the green cells represent uphill flow from the point of interest. Correlation Equation ([Slope ] + 90 >= [Flow] and [Slope ] - 90 <= [Flow]) OR ([Slope] + 90 - 360 >= [Flow] and [Slope] - 90 - 360 <= [Flow]) OR ([Slope] + 90 >= [Flow] – 360 and [Slope] - 90 <= [Flow] - 360) Elevation Aspect Allowable Gravity Flow Straight Line Direction The relative cost of lift stations and demolition of an existing structure is factored in to the raster calculator to produce a total cost raster based on the given point. Finally, a cost weighted allocation is created to find the optimum existing portion of the wastewater system that the new pipeline will tie in to. This allocation is based on relative cost values of distance, slope, and land use. Results The following results for a given location produce an allocated raster to determine the best location. The results are based on a straight line cost weighted distance with some preliminary assumptions for cost values. Land use and slope are the main factors of the final allocation. As shown, the optimum location is to the portion of pipeline identified as 311. Conclusion An automated process can be achieved using a Visual Basic approach while following these guidelines and correlation equation. Other alternative design approaches may include a correlation of usage which will determine the optimum size of the pipeline to be installed.