Rains, the Watershed and Pollution -- Part 1
From the MBNEP Volunteer Monitoring Program
This rainy season has begun with a real downpour, and it's not even winter yet. The rainfall brought the dusty, dry lower reaches of Chorro Creek back to life, and is more than welcome after back to back drought years. But it's a mixed blessing for everyone concerned with clean water: while the rain falls as pure water, it doesn't stay that way for long after reaching the ground. The clean look and feel of our towns after a good rain comes at a price.
In this two-part article, we'll take a look at how and why rain can be linked with pollution problems, as well as what can be done to help assure that an increase in rainfall doesn't degrade local water quality. Part one will look at watersheds and how geography plays a role in this process. In part two, we'll dig deeper into what the pollution threats are and how we can solve them.
To understand how rain can play a part in pollution problems, it's important to understand what a watershed is.
Simply put, it's the area of land that drains into a common creek, stream, river, estuary, ocean, or other body of water. Every square inch of land drains somewhere, usually through a network of increasingly larger streams and creeks. Watersheds vary in size drastically. The Mississippi-Atchafalaya River Basin, the third largest in the world, drains part or all of 31 mid-western states and two Canadian provinces. The Morro Bay Estuary watershed, on the other hand, consists of just 48,000 acres including the community of Los Osos, part of Morro Bay, Cuesta College, and the California Mens' Colony.
The geography of a region dictates the boundary of the watershed, creating something like a bowl with one side open to the creek, river, estuary, or ocean. High points like mountain ridges, hill tops, or even a slight elevation rise create separation lines between watersheds. With a little practice, it's easy to identify these real-world geographic equivalents of the line on a map.
In the Morro Bay Estuary's watershed, a matrix of smaller creeks direct runoff into Chorro Creek, draining the region around Highway 1 known as the Chorro Creek subwatershed, while Warden Creek and Los Osos Creek drain the Los Osos valley. Both join the estuary at the salt marsh abutting South Bay Boulevard.
When the rain is pouring down, it's not difficult to imagine how something unsavory (imagine your pollutant of choice) deposited almost anywhere in our watershed will inevitably make its way to the nearest creek or storm drain, and from there down to the estuary. With our long dry season, pollutants may stay put for quite awhile, but once the rains start they're quickly flushed downstream. Rain rinses the watershed clean but concentrates the pollutants into the estuary. The end result is that anything occurring within the large land mass of the watershed will affect water quality, and very small pollution events, even things as seemingly inconsequential as over-fertilizing your lawn, failing to pick up pet waste, or a small motor oil spill, combine to create serious problems.
At the Estuary Program, a great deal of our work in preserving and restoring the estuary happens in the watershed and not just the estuary itself.
The Environmental Protection Agency considers a watershed approach "the most effective framework to address today's water resource challenges. Watersheds supply drinking water, provide recreation and respite, and sustain life. More than $450 billion in food and fiber, manufactured goods, and tourism depends on clean water and healthy watersheds."*
In part two of this report, presented in the December issue of the Journal, we'll look into the specific kinds of pollutants impacting Morro Bay and other watersheds, and what we can do to keep our waters clean.
*From the EPA's Watershed website. This site is a great resource to learn more about watersheds.
More information on this and other estuary related topics can be found at the Morro Bay National Estuary Program website.
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