When a drop of water falls, where does it go? It all depends where it is in the watershed. A watershed is an area in which all the surface water drains to one place, such as a stream or river plus the land around it that drains into it. Watersheds are like nesting dolls, with each one fitting into the next. For instance, in Birmingham, Village Creek is part of the Locust Fork Watershed, which is part of the Black Warrior River Watershed, which is part of the Mobile River Basin. That means that water that flows into Village Creek ends up in the Mobile River and the Gulf of Mexico.
Those connections between watersheds mean that what we do can have an impact many miles away. Watersheds don’t just contain forests; they also include parking lots, back yards and storm drains. The fertilizers we put on our lawns and the oil that drips from our cars are washed by rains and drain into local creeks and streams and flow into rivers – which we depend on for clean drinking water — and, eventually, the sea.
Alabama’s waterways are famous worldwide for the diversity of wildlife they support. The state has more types of crayfish, fish, snails and mussels than any other state in the nation. Many of the species unique to Alabama are found in the streams in and around Birmingham.
For example, the Cahaba River, which flows through metropolitan Birmingham, is home to more than 131 species of freshwater fish, including 18 found nowhere else. There are dozens more rare mussels and snails and a huge variety of plants, including the elegant Cahaba Lily, which draws crowds when it blooms each spring. At the same time, more than a million people depend on the Cahaba for drinking water, another good reason to keep it clean.
That’s easier said than done, because more than water flows through a watershed. A stream also carries sediment, the nutrients released by decomposing plants and the minerals that dissolve out of rocks. There’s water that we can’t see that soaks into and moves through the ground – called groundwater – until it eventually emerges in streams. So the land the river flows through is also a crucial part of every watershed.
Birmingham claims more watersheds than most cities, thanks to its complicated geology and hilly terrain. That means that streams that may be close to each other as the crow flies may flow for miles before they connect. With that in mind, there are two main watersheds in our area, one on each side of Red Mountain.
On the south side of the ridge, water flows into the Cahaba River, the source for about a quarter of Alabama’s drinking water, which ends when it merges with the Alabama River near Selma. The Alabama then joins with the Tombigbee to form the Mobile River, which empties into the Mobile Bay and the Gulf of Mexico.
On the north side of Red Mountain, water flows into the Black Warrior River watershed, which lies entirely within northwest Alabama. The river begins 20 miles west of Birmingham at the confluence of the Locust Fork and Mulberry Fork. It joins the Tombigbee River in Demopolis; the Tombigbee then continues south and is joined by the Alabama River near Mobile. Although the Black Warrior River isn’t in the city of Birmingham, many of the city’s creeks end up in it, including Turkey Creek, Five Mile Creek, Village Creek and Valley Creek.