Drainage Basins - How They Affect Buying A Home
Potential home buyers take a lot of factors into account when they look for a house, but seldom do they think about its location in terms of geology. It just seems too abstract, too distant. Yet how distant or abstract is it when a flood washes through your house, carrying half of your possessions with it? How distant is a rock or mudslide that buries the house you just bought? This happens more often than you might think.
Floods & Mudslides
In 2011 there were massive floods in the central United States from a combination of high snow melt and intense rainstorms. In 2010 heavy rains and mudslides in Southern California washed tons of debris down from nearby mountains. In 2005 Hurricane Katrina and broken levees devastated New Orleans (which would not exist anyway, had the Mississippi River been allowed to change its course naturally).
These are all occurrences that would not have destroyed so much property, if builders had honored Nature's own water drainage systems and built appropriately. What is a drainage system and how does it function? What does it have to do with buying a home?
Drainage Basin or Watershed
A drainage basin consists of mountains that block rain or snow clouds, and all of the land below them that catches the rainwater or snow melt, stores it in an aquifer, and guides the flow via rivers and streams toward a larger body of water, like the sea. Most drainage basins appear fan-shaped from the air, with numerous runnels made by water flowing down the mountain, and meeting at the bottom to form streams, which gather into rivers that flow to the sea.
Nested Drainage Basins
Small drainage basins (called watersheds in North America) flow into larger ones, which may or may not end in an ocean. The Mississippi River has seven river systems flowing into it, each with their own drainage basins, some more than one.
Those basins that end in a river that flows to an open ocean are called "river basins". The five biggest river basins in the world (by area) are the Amazon (NE South America), the River Platte (SE South America), the Congo (Central Africa), the Nile (NE Africa), and the Mississippi River system (Central United States).
Those that pump out the most water in volume are the Amazon, the Ganga (India), and the Congo basins. All of these river basins consist of collections of smaller basins that empty into them.
Drainage basins don't always empty into a sea. Some end at lakes with no outlets that disappear into the ground or are lost to evaporation (endorheic basins). Angola's southeastern drainage basin flows into Botswana's Kalahari Basin, where it ends at the Okovango Swamps that hosts one of the most diversified wildlife areas in the world. Most of Central Asia's rivers flow into the Caspian Sea - the largest inland body of water in the world.
The pattern of human settlement naturally falls into occupation of a drainage basin, starting with hunting or farming near the center of a basin and fanning out, or discovering minerals in the mountains and spreading down into a basin from there. Communities are formed in the basins, with neighboring basins being considered a separate community - separated usually by higher ground.
The higher ground, which splits the direction water flows into different basins, is called a "drainage divide" (or in much of the world a "watershed"). The map on the right shows the drainage divide boundaries of all the major river basins in the U.S.
Note that the only part of the U.S. that has no rivers is the southwest, mainly Nevada and Southern California - hence the long term struggles for water supply there.
Southern California Drainage Basins
In Southern California, mountains are typically chaparral biomes - a type of highly flammable bush, whose burned oils make the soil waterproof. Typical of that biome is wildfires followed by erosion from rain, then massive mud and rockslides that push everything out of their way, including houses. Although government officials have built debris dams up and down the mountain range to hold the debris back, the dams need continual cleaning out or they get pushed over too.
The entire land between the mountains and ocean is made of eroded material - like a giant beach that sits on rock. All of that rocky, sandy, silty material pushed down by storms from the mountains forms a series of deep aquifers, or water collection basins, which is where Southern California used to get its water, before civilization used most of it up.
In spite of the geologic instability of the region, which includes earthquakes, with mountains continually eroding and floods continually causing mudslides, almost all of Southern California is now city - a massive city with elaborate structures that pipe water in from rivers hundreds of miles away, and other structures that clean up used water in an attempt to refill aquifers blocked by concrete that used to fill naturally with rain.
California's officials feel helpless to stop the flow of civilization, although they are doing the best they can to satisfy its needs. Expansion continues, most likely out of ignorance, with developers building in slide-prone areas and buyers buying what they built.
- Southern California storms save worst for last - Los Angeles Times
The first rumblings sounded like cracking thunder. "When you hear the boulders going 'Bang, bang, bang,' you know there's going to be problems," said Steve Eighart, who lives in Orange County.
Factors in Choosing a Home
Home buyers who choose to live in disaster-prone areas, like Southern California or New Orleans, usually do so because it's beautiful or because property is cheaper there - until a disaster hits. Those who are at all conscious of the trade-off they are making, wisely purchase disaster or flood insurance to back them up, which adds long term costs to the property.
If you want to avoid those costs and keep your new house safe, these are some of the things to look into, depending on the area where you are interested in buying:
- Potential flooding events - How often does it naturally flood in the area? What are the hills like? Is there a danger of rock or mudslides when it rains a lot? How far out from the hills do the slides go? How long does it take for floodwaters to subside?
- Ground instability from earthquakes, slides, or subsidence (sinking from groundwater drainage) - Such events can crack the foundation and/or walls of your house, if not destroy it entirely.
- Disjointed handling of watershed issues - One or more communities or manufacturers making decisions that affect communities downstream. Better to have one overall body managing the entire watershed with input from those affected.
- Increasing development and too much pavement - Increased flooding and stormwater runoff, loosened soils, and an aquifer blocked from refilling by rain.
- Bacterial contamination of local water sources (cryptosporidium, etc.) - What activities are carried out near the river or stream? Is house or building sewage discarded there or is it sent to a special facility?
- Pollution of local water supplies from mining or oil residues, discharge from manufacturers, or agricultural runoff - Not only does pollution destroy stream life, but it can also contaminate the drinking water and make you unhealthy.
- Unclean streets, with garbage collected at storm drains - This shows a general lack of caring for the watershed and potential ignorance of problems that could arise.
- Regular passage of rail cars or trucks carrying oil or other contaminants - Such contaminants often leak into the groundwater.
- Road conditions - Are they well kept? In which areas are they run down and how did they get that way? How long does it take for road maintenance crews to respond to calls?
Research Weather Events
Past weather events can tell you a lot about an area, it's potential threats, and the way officials have dealt with the results. You'll want to know what happened, when it happened, how extensive it was, who was hurt by it and where they were located, and how officials responded.
A prevalence of minor, rather than major events, with responsive officials who cleaned up quickly afterward is a good sign. Best yet, you're looking for locations to live that are away from disaster prone areas. Where can you get this information?
Real Estate Agent - Your agent should know the types of housing available in all areas of the city or town where you want to live. They'll generally know road conditions and may know many of the officials you will want to talk to. They should also be able to help you with information about weather patterns, although they may not be wholly honest, if they want to sell you a particular place.
Watershed Authority - This is usually somebody in city government, like a land use planner (who will at least know who to go to), or it may be a regional flood control body. If the department is large and has many specialists, that tells you the frequency and types of weather events are probably high. Look for a phone directory and analyze based on it. Then call someone with your list of questions.
Environmental NonProfits - The Internet is usually the best place to find information on local environmental nonprofits. If the information you are looking for is not on their website, they will generally be eager to talk with you in person. They can be a fount of useful information.
Local News Outlets - Here is where you can find the best news about traumatic events resulting from weather extremes or drainage basin collapses of any kind. Calling the front desk will usually get you an answer faster than doing a search on the Internet. Plus you can ask for more information that might not be in the news reports - like their personal experience of the event.
Home Insurance Company - Insurers are an excellent place to get information about disasters in watersheds, since many homeowners receiving damages will have filed claims. Call your own company or look in the yellow pages to see which companies are most active in that area. Find out what the claims are generally for, how extensive they are, and where they are located.
Your Personal Experience
Have you ever been in a serious natural disaster?
Homeowners Flood or Disaster Insurance
Some people deliberately choose not to do this kind of research, assuming that they can get disaster insurance that will cover anything that might happen. Sometimes that is true, but if your insurance company has any inkling that you were warned ahead of time and ignored it, they will refuse to pay.
Locating a house directly in the path of regular flooding will be suspect. Building in the middle of a fire zone will be suspect. Refusing to relocate when local officials have repeatedly warned of an upcoming rock slide will definitely generate a refusal to cover damages, as did happen in Southern California a few years ago.
Insurance companies like to make money from your premiums and do not like to be ripped off. They are committed by law, however, to following through with legitimate claims, so do the work necessary to choose your location well. It will save you hassle with them, if you should need to file a claim later, and also save you the hassle of cleaning up a destructive mess that didn't need to happen in the first place.
Meanwhile, if you have followed the steps above before picking a home to buy, you will likely have already identified the safe places to live. Even though you might not get the prettiest or cheapest place, at least to won't have to worry about losing your new home to a disastrous event you could have avoided.
- Science for Kids: Watersheds | USDA Forest Service
- Explore Your Drainage Basin in Google Earth
Input your geographical location and let Google Earth show you your local drainage basin.
- USGS Water Resources: About USGS Water Resources
Water resources information from the US Geological Survey.