Information Management for County Infrastructure

Information Management for County Infrastructure

Bryan T. Claxton
GIS Specialist, Burns & McDonnell
9400 Ward Parkway, Kansas City, MO 64114

In the mid-1980's the Johnson County Board of Commissioners initiated the Automated Information Mapping System (AIMS). AIMS was developed to enable the county to meet the growing mapping and documentation demands of the Kansas State Legislature. In addition to meeting the requirements of the legislature the county realized the overall benefit of having accurate and current maps available to the cities and citizens of the county and AIMS has been growing ever since.

One of the latest endeavors of AIMS was to compile new planimetric data. As a part of the new planimetric data, contours were developed for the entire county. This elevation information could then be used to support stormwater studies. These stormwater studies are being completed on a watershed by watershed basis and submitted to the county in a form that will supplement their enterprise GIS system. Upon completion of a watershed, methodologies were analyzed and passed on to the next study so as to refine the process and run each one as efficiently as possible.

Burns & McDonnell is tasked with completing the third stormwater study, for the Mill Creek Watershed. The study includes a hydrologic analysis utilizing the HEC1 modeling software and a hydraulic analysis utilizing the HEC-RAS modeling software. The study will analyze the 100-year flood plain and determine where changes need to be made to the current FEMA boundaries. In addition to re-mapping the floodplain the county is using the project as an engine to supplement their enterprise GIS system.

Project Philosophy
The underlying philosophy of this study is information management. The county realized the importance of information management and is using projects such as this watershed study to build and supplement their enterprise information management system. In order to make each project a building block in their information management system the county sets up standards and requirements for the project deliverables. The data requirements that the county sets allow them to take the deliverable materials from any project and integrate them directly in with their current information. In this way the county can keep their information current without having to go out and do an inventory of their system. They always have a current baseline and cut out on the need to go back to square one whenever they have a new project. A little bit of initial effort on the county.s part to set up these type of standards and requirements will make the maintenance and operation of their enterprise information system much more efficient and cost effective.

In addition to the information aspect of the project, public involvement and input is given a high priority due to the impacts of flood plain re-mapping. A number of public meetings were held to inform the public of what was being done and alert them to the presence of survey crews that would be collecting field information. In addition to the meetings, a project website was developed. The website is updated on a weekly basis and provides the public a current information source about the project.

Project Phases
The stormwater study can be broken down into five major phases or steps. The initial steps deal with setting up a foundation on which the rest of project will operate and the last step is the delivery of the flood plain analysis for the watershed.

The first phase of the project is to come up with a database design that will house all the data and serve as the central file cabinet for the whole project. The design of the database is partly set by the county's data standards and the need to make sure that the information could be used efficiently for this study as well as any future studies or projects.
The second phase of the project is the collection of all the required data for the stormwater study. This phase included attaining the county's current planimetric data as well as the collection of new field data.
The third phase deals with supporting and developing data for hydrologic stream model.
The fourth phase deals with supporting and developing data for hydraulic stream model.
The final phase is the culmination of all the modeling into new flood plain delineations for the watershed.

Database Design
The foundation of the watershed study is the database that is set up to house all of the information. This database design has to facilitate integration into the county's current GIS database and feed applications such as the stormwater models. To meet this need, the county and Burns & McDonnell decided upon a database developed with SQL Server and Arc/INFOTM with the Spatial Database Engine.

Figure 1 shows the entity relationship diagram for the Mill Creek watershed study. The main linkage for all the information is with the stream network. Since the stream network is the focal point of the database its creation is given a high priority early in the project and will be a valuable piece of information to be added to their information management system.

Data Collection and Survey
The base data used in the study is drawn from the new planimetrics that the county has compiled. These data sources included the roads, hydrology, parcels, buildings, edge of pavement, contours, and water conveyance structures. The new planimetrics have just been completed by the county and provide an up to date baseline of information that is very helpful when doing a watershed study such as this.

The additional data that is required for the study deals with the exact specifications of the water conveyance structures. This information must be surveyed in the field and loaded into the database. A criterion was set by the county that all structures having a contributing area of 160 acres or greater would be modeled. In some cases engineering judgement and field knowledge are drawn upon to extend past the 160 acre criterion to characterize known trouble areas. The location of the structures that meet this criterion is identified with the GIS using ArvViewTM, with the 3-D Analyst and Spatial Analyst extensions. The entire watershed is broken down into six main sub-watersheds to make Stream Network Table data collection easier and facilitate multiple tasks being done at the same time. In some cases engineering judgement and field knowledge were drawn upon to extend past the 160 acre criterion to characterize known trouble areas.

Once all of the locations that need to be surveyed are identified field crews go out and survey each water conveyance structure. At each structure pertinent information is collected dealing with bridge or culvert face dimensions, upstream face cross sections, and road decks. In addition to this survey data, digital photos of each structure are taken and logged with a unique identifier to that structure. The attributes collected at each structure are defined in the database and collected so that they can be loaded into the database with minimal effort.

As the water conveyance structures are surveyed new benchmarks are set throughout the watershed. A total of 153 new benchmarks are set in the Mill Creek watershed. The benchmarks will be beneficial to the county for the stormwater study as well as in future construction and surveying endeavors. The stormwater study provided an opportunity for the county to set these benchmarks when it might not have been feasible to do otherwise. This is one more example of taking advantage of a project to supplement an information management system.

Hydrologic Data Development
As the field survey work is being completed the data development to support the modeling is going on in the office. The hydrologic modeling for this study is done using the U.S. Army Corps of Engineers Hydrologic Modeling Center model HEC1. This model is used to determine the flows in the stream network throughout the watershed. In order to feed this model Arc/INFOTM and ArvViewTM are used to manipulate the county's planimetric and elevation data.

The first step in generating the data for the HEC1 model is to take the hydrology from the planimetric data and create a fully connected stream network. This was started during the process to determine which water conveyance structures would need to be surveyed. At this point, though, the stream network extents that were determined from the initial 160 acre criterion are pulled out and cleaned. The cleaning of the stream network involves heads up digitizing a stream centerline in Arc/INFOTM for every portion of the network that had a width greater than 10 feet. This is necessary because the planimetric hydrology file contains water edges for every stream with a width of 10 foot or greater and not a stream centerline. Coupled with this fact was that whenever the stream went through a conveyance structure or underground it was not captured in the hydrology file. The result of all this work is a stream network that is fully connected and topologically correct for the entire watershed. The stream network will be delivered to the county as an Arc/INFOTM coverage so that they will not have to go through this exercise of heads up digitizing the next time they do any type of stormwater project for this watershed.

With the stream network complete, focus is turned towards the analysis of the watershed terrain. As mentioned earlier, ArvViewTM Spatial Analyst and 3-D analyst were utilized to help determine what water conveyance structures should be surveyed. In order to do this a triangulated irregular network (TIN), flow direction grid and flow accumulation grid is developed for each of the 6 sub-watersheds in the Mill Creek watershed. The development of these data layers is done with the Hydro tools extension for Spatial Analyst. In addition to the grid files a point file is created for each sub-watershed that contained the location of the desired pour points. The pour points are set at water conveyance structures and major stream confluences. Additional pour points may be set other places to split up a large sub-basin or better delineate a particular area. The pour points and grids are used with an avenue script to delineate the sub-basin area contributing to each pour point.

Once all the sub-basins are delineated the integral data that will be used by the HEC1 model is extracted. The bulk of the remaining data generation deals with the determination of the runoff curve number for each of the sub-basins. Some of the other data that is developed includes: maximum flow path lengths and slopes, closest rain gauge station to each sub-basin, and stream centerline lengths and slopes.

Two options present themselves for determining existing conditions run off curve numbers. One option is to use a landuse coverage to determine the percent impervious areas or alternatively, use the planimetric data to determine a percent impervious. The latter of the two options is chosen because using the planimetric data will provide a more accurate account of the actual impervious areas in the watershed. Therefore, the coverages containing roads, buildings, driveways, and edge of pavement are combined to yield a true impervious area coverage for the entire watershed. With the impervious area coverage built it is then combined with the soils data to determine an existing conditions run off curve number for each sub-basin.

The planimetric data is also used to develop a set of representative percent impervious tables for the Mill Creek watershed. The tables give percent impervious values for each landuse in the study area and can then be used in determining the future conditions run off curve numbers. This is necessary since only landuse will be available to determine future conditions information. This method will calibrate the percent impervious values to the historical development trends in this watershed and will be better than using a set of default book values. The tables will be provided to the county as a deliverable so that they will be able to reproduce everything that was done in this study as well as provide the information to anyone who does future studies in this watershed.

Hydraulic Data Development
The second step in the modeling of the watershed is to take the flows from the hydrologic model and put them into a hydraulic model. In this case, the hydraulic model used is the U.S. Army Corps of Engineers Hydrologic Engineering Center. HEC-RAS. The HEC- RAS model takes the geometry of the watershed and combines it with the flows extracted from the HEC1 model to determine areas of flooding. This model works in conjunction with the GIS very well and has a long reputation as being dependable.

The data that HEC-RAS requires is basically just a 3-D representation of the watershed area and flow values. In order to get this geometry information, a package of arc macro language (AML) macros has been developed by ESRI and HEC that extracts this data. The package is called HEC-GeoRAS and the version used in this study operated within Arc/INFOTM. The HEC-GeoRAS package uses a digital terrain model and Arc/INFOTM coverages to create a text file that is formatted such that the HEC-RAS modeling software can import it. A lot of time and effort is saved by using GIS tools to generate the geometry files instead of doing it all by hand and this method allows the model to be reproduced at any time because it can be extracted from the information in the enterprise database.

A detailed discussion of the HEC-GeoRAS package will not be included here, but rather a quick overview of what was needed to run the package. If a more detailed discussion of the HEC-GeoRAS package is desired the software and documentation are available at the HEC website ( http://www.wrc-hec.usace.army.mil/ ). The three pieces of data that are mandatory when generating a geometry file are the digital terrain model, stream centerline and the cross section cut lines. In addition to these three things the overbank locations and the flow path locations may also be added into the geometry file.

For this study the hydraulic modeling will be done on a sub-watershed basis just as the HEC1 modeling was done. Upon completion of all of the sub-watersheds they will be combined into one larger file that will incorporate the entire Mill Creek watershed. Each of the sub-watersheds has a set of coverages that are used for HEC-GeoRAS. The coverages are developed through a combined effort of the GIS team and the hydrologic engineers on the project. The cross section cut lines, over bank locations and flow paths are all heads up digitized in ArvViewTM and then converted to Arc/INFOTM coverages for use in the HEC-GeoRAS package.

Mapping the new flood plain
The culmination of all the modeling efforts is the mapping of the 100 year flood plain for the watershed. The study has not reached this stage currently but will rely on the HEC- GeoRAS software package once again, to provide the tools necessary to map the new flood surface. Once the new flood plain has been mapped it will be submitted to FEMA for review and eventually, update of the current flood plain maps. These new flood plain boundaries will also be added into the county's information management system and will be available for many different planning applications.

Conclusion
The primary goal of this watershed study is the mapping of the 100 year flood plain but the real benefits of the study are much greater than just the mapping of the flood plain. Granted, whether the information management aspect of this project is present or not the flood plain analysis would still be done but the county would be short changing themselves because of all the opportunity they left out on the table. Johnson county has chosen to grab every opportunity they can to work towards a future goal of enterprise information management for all systems in the county. They may not be where they want to be right now but are using opportunities like this watershed study to work towards their goal. A little for thought in the mid 1980's and looking at all the opportunities in each project they need done has set the county up with a information management system capable of aiding in any number of activities.