When the rain lands on your roof or driveway, you can hear it run through the gutter or watch it run down the street. You might be surprised to see where it goes next. And that knowledge could encourage Pierce County residents to better understand how their daily actions impact local waterways.

Using innovative GIS technology, Pierce County has launched a Web site that enables residents to choose an address on a map and track the flow of water as it leaves their property. This water, called stormwater, picks up pollutants such as yard chemicals, pet waste and car oil leaks as it flows over our yards, driveways and streets.

The site, called Where Does The Water Go? ( http://matterhorn11.co.pierce.wa.us/waterflow/ ), is among new or enhanced online tools that Pierce County operates for the public to better understand the environment around them. The County is unveiling the sites in coordination with GIS Day 2009, a global event that highlights the benefits of global information systems to address planning, emergency and environmental issues.

The stormwater site enables users to pinpoint an address or location on a map, and then GIS technology calculates the direction and flow of stormwater based on topography. It traces the water’s path as it flows to ditches, ponds, lakes, streams, rivers and Puget Sound.

“By better understanding where stormwater runoff goes, Pierce County residents can help prevent water pollution, flooding and other impacts to our local waterways,” said Pierce County Executive Pat McCarthy. “This is a great resource for us all to see how our daily activities affect the natural resources that make this such a wonderful place to live, work and play.”

The stormwater site is just the latest example of Pierce County’s use of GIS technology on behalf of its residents.

The County’s Public GIS site ( http://matterhorn.co.pierce.wa.us/publicgis/presentation/map.cfm?Cmd=INIT ) has been enhanced to include aerial photographs that are adjusted for topography, lens distortion and camera tilt to provide a more accurate representation of the Earth’s surface. Known as orthophotos, these resources provide students, businesses and the general public with greater detail about physical features in their communities.

The County’s GIS Division Web site has been improved to showcase new GIS projects and upcoming activities throughout the region. It also provides links to many of the most-used Pierce County Web sites that feature GIS and mapping.

“Pierce County is a leader among governments in using GIS technology to improve services to its citizens,” said Linda Gerull, interim director of the Information Technology Department. “More than 100 clients subscribe to our pay services, including cities, engineering firms and government agencies. GIS Day is a great opportunity for the public to see real-world applications of this technology.”

These Web sites are launched today by Pierce County in recognition of International GIS Day, celebrated worldwide on Nov. 18. It began in 1999 and is held each year on the Wednesday of National Geographic Society’s Geography Awareness Week. A GIS is a computer-based mapping tool that takes information from a database about a location, such as streets, buildings, water features, and terrain, and turns it into visual layers. The ability to see geographic features on a map gives users a better understanding of a particular location, enabling planners, analysts, and others to make informed decisions about their communities.