TERM PROJECT CE 394K GIS
for Water Resources
Fall Semester 2003
Rodrigo A. Nicolau del Roure
“Rosillo Creek Flood
monitoring and mapping in San Antonio-Texas an Emergency Response point of
view”
Part II
This project was developed by Silvana Alcoz and Rodrigo Nicolau del Roure. It was divided in two parts. Part I was done by Silvana which describes basically our interest in this issue and how we obtained the data needed. Part II by Rodrigo which describes the use of this information and this GIS tool in the emergency response itself.
INTRODUCTION
Only
after floods many people with damaged homes realized they lived in a floodplain.
In many communities, floodplain maps are outdated and inaccurate or do not
exist, making it difficult for local officials to manage floodplain use
effectively.
Let’s start with a basic question, What is a Flood?
According to FEMA, floods are one of the most common and widespread natural disasters. In the United States, most communities have experienced some kind of flooding, after spring rains, heavy thunderstorms, or winter snow thaws.
A flood can be defined as a general and temporary condition of partial or complete inundation of two or more acres of normally dry land area as a direct cause of:
- overflow of inland or tidal waters,
- unusual and rapid accumulation of runoff
- a mudflow
What is a 100-year Floodplain?
“Webster’s” dictionary defines a floodplain as “level land along the course of a stream or river that was formed by soil deposited by floods, may be submerge by floodwaters”. There are many levels of floods: 500-year, 100-year, 25-year, and 10-year. These numbers indicate the likelihood that a particular area will flood in a year's time. For example, a home in a 100-year floodplain has a one in 100 (or 1 percent) chance every year of being flooded. That percentage holds true every year, regardless of how many floods have occurred in previous years, or their severity.
Tropical
storm Allison, Houston, TX, 2001
Floods can be slow or fast rising (flash flood) but generally develop over a period of days (hours or minutes in the case of flash flood). Emergency management and response procedures may include several activities to prevent an emergency, reduce the chance of an emergency happening, or lessen the damaging effects of unavoidable emergencies. Investing in mitigation, such as, engaging in floodplain management activities, constructing barriers, such as levees, and purchasing flood insurance will help reduce the amount of structural damage to properties and financial loss from building and crop damage should a flood or flash flood occur. Finally, but as important as the ones stated before are the response procedures of the emergency teams (Fire, Police, EMS, other City Departments) that assist people and property endangered by floods.
This project has as main objective to show the importance of the use of early warning tools such as NEXRAD complemented with GIS to predict, model and map flood areas and its application to enhance and safely manage emergency response teams.
MODEL INTEGRATION FRAMEWORK FOR FLOODPLAIN MAPPING OF ROSILLO CREEK
The idea is the integration of GIS and a model of a particular geographic characteristic or phenomena of interest. In this case, a spatial framework is used to represent multi – model and GIS integration of the hydrologic and hydraulic components of the San Antonio Basin Modeling Project, specifically for this semester project, the Rosillo Creek (as part of the Salado Creek pilot basin study of the whole project), have been defined (preliminary), designed and implemented. This is possible because a technology such as GIS allows for the analysis of the spatial component of the data to possibly reveal trends, relationships and patterns. A GIS allows for the integration of this graphical data, often in the form of maps, with descriptive or attribute information from a wide-variety of existing databases. Therefore, a GIS becomes much more than a mapping tool, as it is often considered. It is a database that can be queried and manipulated as any other database management tool but one with the additional advantage of displaying data in a more understandable format. Another significant advantage of this type of data management and display is that critical relationships between these varying data are often only recognizable when displayed in a geo-referenced framework. With the advances in computer science and microprocessor technology the different software have been able to facilitate the share of data between them and the graphic results.
Basically for the model framework we look for a system that will integrate geospatial data, rainfall data and calibration data. All this combined in a way that the different hydraulic and hydrologic models share results linked through archydro, will set the boundaries of a model system and this model system will allow to manage floodplains and forecast floods as well as to become a tool to enhance capital improvements in planning and help in regional water resource planning.
Source:
PPT presentation, CE 394K Fall 2003, Prof. D. Maidment, University of Texas at
In the case of the San Antonio River Basin Modeling Project and in particular in the Rosillo Creek pilot study, spatial linkages were proposed using GIS representations of stream networks and water features of the region. Hydrologic models, specifically HEC-RAS and HEC-HMS were linked using DSS (HEC-DSS in this case) which is a “library” or as the mnemonic indicates, a Data Storage System. This DSS allows linkages, storage, retrieval and manipulation of information “connecting” this utility programs. Finally, through ArcHydro, they determine water surface elevation and flow as a function of rainfall and consequent runoff. This is possible because ArcHydro provides a structure for storing geospatial and temporal information, facilitating the linkage of this data with the hydrologic models mentioned before
A schematic showing the interrelations between HEC-HMS and HEC-RAS
Source:
PPT Presentation CE 394K GIS in Water Resources Fall 2003, Prof. D.Maidment,
University of Texas at
The Model works like this (in simple words):
- Precipitation information is captured and stored by NEXRAD. This data is in the form of text files. Time series are created and transferred to geodatabase tables with ArcHydro format. At the same time, HEC time series tables are stored and connected to HEC-DSS.
- The time series records associated with NEXRAD are mapped in ArcHydro into each watershed. The corresponding watershed will have rainfall – runoff and this data will be transformed using HEC-HMS into water flow.
- HEC-RAS enters into play. Linked through HEC-DSS, it uses the flow information to determine cross sections and elevations. These results are relayed to ArcHydro which again will map the data to the corresponding watershed.
- The elevations (in xml format) and corresponding cross section are used for interpolation and generation of water surface TIN. This water surface TIN is related to the flood plain boundary and converted to raster format. The raster is then intersected with the terrain raster to determine water depth (in raster format also). Finally, the depth raster is converted into a polygon and allows the generation of the flood inundation map.
All this process is called Map 2 Map. Schematically it looks like this:
Source:
PPT Presentation CE 394K GIS in Water Resources Fall 2003, Prof. D.Maidment,
University of Texas at
NEXRAD
NEXRAD stands for Next Generation Weather Radar and was established in 1980 to replace aging radars across the US. The NEXRAD is also known as the WSR-88D (Weather Surveillance Radar 1988 Doppler).
NEXRAD is used to warn the people
of the United States about dangerous weather and its location. Meteorologists
can now warn the public to take shelter with more notice than any previous
radar. There are 158 operational NEXRAD radar systems deployed throughout the
United States and at selected overseas locations. The maximum range of the
NEXRAD radar is 250 nautical miles. The NEXRAD networks provides significant
improvements in severe weather and flash flood warnings, air traffic safety,
flow control for air traffic, resource protection at military bases, management
of water, agriculture, forest, and snow removal. (Source:
www.noc.roaa.gov)
A main
characteristic is NEXRAD’s ability to detect wind patterns in storms and
provide real time rainfall amounts are revolutionizing the way we keep up with
and ahead of rapidly changing weather. Each NEXRAD
radar generates dozens of data types, including higher resolution reflectivity
data, storm total rainfall amounts, wind speeds and direction, wind gusts and
much more, including early tornado detection capability. This accurate detection of circulations
associated with tornadoes and other severe weather phenomena increase advance
warning, and the specificity of such warnings to help save lives and protect
property.
This is how it works: NEXRAD Doppler radar processes the radar's reflected signal to determine the location and intensity of precipitation (reflectivity products or feed back from Doppler radar’s signal), the wind speeds toward and away from the radar site (radial velocity products) and many other products. This information goes directly to computer systems, which create easy to read color displays of the NEXRAD information for each individual radar, and combine information from all radars to create mosaic displays.
(1):AccuWeather's Real-Time Regional NEXRAD Radar images show you where the
storms are right now, and how intense they are; (2): To see how much rain is falling from the storms, consult
1-Hour, 3-Hour, or Storm Total Precipitation NEXRAD graphics.
Source:
www.accuweather.com
NEXRAD Doppler radar data is gathered at a high resolution out to a farther distance from the radar site than conventional radar data, .6 by .6 of a mile resolution out to 143 miles for NEXRAD Base Reflectivity data, as opposed to similar resolution out to only 66 miles for conventional radar. And NEXRAD data depicts 16 data levels, as opposed to only 6 data levels that were available with conventional radar.
NEXRAD
Doppler radar is also much more sensitive than conventional radar, allowing
users to see meteorological phenomena never before visible in radar data, such
as blowing dust and dry frontal boundaries that have no associated
precipitation. (source: www.acuweather.com)
NEXRAD DATA FOR ROSILLO CREEK PILOT MODEL STUDY
For the study case, the flood inundation polygons correspond to the following storm events:
FloodPoly1: 01 Jul 2002 at 0400 through 01 Jul 2002 at 2400
FloodPoly2: 14 Jul 2002 at 1700 through 15 Jul 2002 at 1400
Both storms had duration of about 20 hours each. Below are two tables showing some of the time series captured for these events.
For more details open: nexrad timeseries table 1.xls
For more details open: nexrad timeseries table 2.xls
ROSILLO CREEK – NEXRAD MODEL OUTPUT
Now lets get into the interesting part, the results of the model. The model was run by Oscar Robayo, a PhD Student working in the Center for Research in Water Resources at J.J. Pickle Research Campus, The University of Texas at Austin.
Using the geodatabase created by running the model and using ArcMap from ArcGIS we developed a series of maps to understand the results. From the City of San Antonio web page we downloaded files (shape file format) for:
- City limits
- Mayor Highways
- Minor Highways
- Streets
- Streams (rivers, creeks)
- Airports
- Police Stations
- Fire Stations
- Public Schools
- Hospitals
- Orthophotos of the surroundings of Rosillo Creek
CREATING THE FLOOD MAPS
Using ArcMap we can configure our
maps. First open ArcMap. Choose “A new empty map” on the window that pops up.
Add data by clicking on 
.
This will open a window that allows the search of files in layer format
(primarily) and datasets.
Selecting the layers that are of most interest we define our base map.
Now lets take a look to the area of study. Rosillo Creek watershed is located on the east side of the City of San Antonio. If we wanted to know more about the land use, zoning or population density we can find that information on the U.S. Census Bureau web site (this was explained in Part I).
Area
of study and detail To
enlarge click here
To enhance comprehension of the area and have even more details we can incorporate orthophotos. To do so we can download these orthophotos from the Texas Natural Resources Information System web site. The greatest advantage of using orthotphotos is the actual visualization of buildings, streets and other landmarks and features that in reality exist in the area if interest.
Zoom in to area of interest.
To enlarge click here
From the model we have two results, one for each storm event. We can input the data obtained to create the corresponding maps and the model flooding that that was predicted. Using our base map we only have to add the layers resulting from Floodpoly 1 and Floodpoly 2. Adding the layers we have the following maps:
FloodPoly 1:
Click here to enlarge Click here to enlarge
FloodPoly 2:
Click here to enlarge Click here to enlarge
100 YEAR FLOODPLAIN COMPARISON
Most of the data for cities and insurance companies to deal with flood management, mitigation and planning comes from FEMA. Most cities and insurance companies use floodplains for this purpose. The 100 year floodplain for the City of San Antonio is the following:
Click here to enlarge
To compare the results of the model and the 100 year floodplain we overlap layers and build a comparison maps.
PolyFlood1 and 100 year floodplain:
Click here to enlarge Click here to enlarge
PolyFlood 2 and 100 year floodplain:
Click here to enlarge Click here to enlarge
In this first case, it can be seen that in some bridges over minor and mayor highways, the model assume them as blockages. This is a true assumption when flooding occurs. It has to be noticed though that this event was a strong storm, but was in the range of a 10 year flood considering its rainfall and runoff. Therefore, the contours delineated by the model and added to the base map shows a difference compared to the FEMA 100 year floodplain.
Polyflood2 has a smoother contour, resembling the 100 year floodplain, but in a smaller scale of course.
In both cases some streets become overcome by high water. This is clear in the north section of the creek, because it is more developed than the south part.
Both models predict and delineate floods according to their own data input. As mentioned before, in the first event, the mapping shows some anomalies. Even though bridges are barriers, it is not very clear why water spread out alongside and didn’t form the characteristic inverse “V” shape that would be expected.
CONCLUSIONS & FUTURE WORK
The results were presented in the last two sections of this work (model output and comparison of floodplains). We can conclude that the model does work and gives a satisfactory result in terms of mapping. Most of this mapping was done using ArcMap, but this same process will be an output of the model (program) itself in the future (that is its objective, “map 2 map”). This action will save time and tedious and long work.
For emergency response this model can be invaluable. With the incorporation of new technology in assisting emergencies, such as E911 communication centers (enhanced 911), GPS systems and MDC (mobile data computers) on board different emergency vehicles and better and more reliable communication devices, Geographical Information Systems can be a perfect complement.
The information available on the internet and other Data sources can aide on the preplanning of emergencies (as stated by Silvana in Part I), information such as population densities and other demographics, land use, special sites (hospitals, schools, etc). Routes for emergency response can be preplanned, as well as establishing which department or departments should respond (police, fire, street and bridges, etc).
In case a flooding is occurring, preplanned routes and different responses can be monitored by the corresponding emergency center (911 or OEM centers) and as this tool, NEXRAD-GIS(ArcHydro), works in real time, the mapping of the flood can be done in real time (with a small delay), allowing to correct the response routes if they become flooded, increasing the efficiency in the use of the resources and moreover, increasing the safety of the emergency responders (“The rescuers are not suppose to be rescued”).
Source: Austin Statesman American
This project helped us work with ArcGIS and ArcHydro. apply tools that were seen in class as well as used in some of the exercises. We were able to research for data needed for the project and manage it in a way that could be used to explain and present our main objective, show the value of incorporate GIS tools in the planning of emergency response when flood occurs.
As future work we could analyze the same problem having as target Onion Creek in south Austin. The City of Austin (COA) is currently transferring to the new E911 system, along with a set of other improvements in emergency response (GPS, MDC for emergency vehicles). The Watershed Protection Development Department of COA has great knowledge, resources and data for a similar project or to test it under other specific geographic conditions. All this could be of good interest to set a formal implementation and use of the model.
Some of the results (floodplain maps) should be analyzed more carefully to determine if there is any flaw in the model. This comes specifically from the results of Polyflood1 and its results.
ACKNOWLEDGEMENTS
• Professor David Maidment, UT
• Oscar Robayo, UT-CRWR
• Ross Clark, City of Austin Watershed Protection & Development Review Department
• Christine Thies, City of Austin Fire Department GIS-Planning Office
• Each and every member of Class Fall 2003, CE 394K GIS in water resources
REFERENCES & RELATED WEB SITES
Getting to know ArcGIS desktop, Robert Burke, Laura Feaster, Carolyn Groess, Eileen Napoleon, Tim Ormsby, ESRI Press, 2001
ArcHydro, GIS for Water Resources, David R. Maidment (editor), ESRI Press, 2002
Floodplain Mapping Using HEC-RAS and ArcView GIS, Eric C. Tate, M.S.E., Graduate Research Assistant, CRWR Online Report 99-1, CWRW University of Texas at Austin, 1999
Emergency Management Basic Plan,
City of San Antonio, Texas, USA,
www.sara-tx.org San Antonio River Authority
www.srh.noaa.gov/radar/radinfo/radinfo.html For more info about NEXRAD
www.fema.gov/hazards/floods FEMA flood web page
www.ci.austin.tx.us/watershed/flood.htm COA Watershed Protection
Development Review, “Flood Control and Safety”
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