Your water is in detention (ponds)

[This is part of a series of posts exploring how a midsized Texas city gets its water. For the first post, click over to see what it takes to fill up a lake.]

In the broadest sense, Abilene has two sources of water: recycled and surface water. Surface water is the water that we draw from the three lakes (Fort Phantom Hill, Hubbard Creek, and O.H. Ivie) as well as the water we scalp from the Clear Fork of the Brazos river. We’ll look at scalping in another post.

How does the water get to these lakes?

Of course rain falls on the watershed of these lakes, but it then has to find its way to the lake. In the case of Fort Phantom Lake, it actually flows through Abilene. While driving around
town, the water (and trash) you see in the ditches and creeks is on its way to your tap.

Abilene_drainage2

Besides creeks and ditches, rain that falls downtown flows into the stormwater sewer system through the drains built into curbs. This water flows straight into the nearest creek to be transported to the lake and thus receives no treatment. This is why you should never dispose of anything but water into sewer drains; it is going straight to your drinking water!

The scenic route

Along the way, the water is diverted in various ways including ponds, detention ponds and riparian wetlands. The latter are the marshy areas often found along the edges of creeks and other water bodies. You might see reeds and cattails along the edges of these places. These wetlands (often ephemeral in this part of the country) provide important ecosystem services to use all. While I’ll let Bill Nye explain it better than I can, you should know that these areas help prevent erosion, fight pollution, provide valuable urban wildlife habitat, and help slow down water to prevent downstream flooding.

Unfortunately, Abilene has removed many of these wetlands in favor of straightening creeks. This is because it is easier to remove trash and treat for mosquitoes in wide straight ditches lined with short grass than in wetlands. It is also an attempt to reduce flooding. Abilene, like many other cities, use detention ponds to slow flood water, collect trash, slow pollution, and other services provided by wetlands. There are approximately 200 detentions ponds scattered through Abilene, though the Abilene Storm Water Department only inspects and maintains slightly under 50 of these ponds.

Detention pond in eastern Abilene before a rainstorm.

Detention pond in eastern Abilene before a rainstorm.

As I will mention in the following video, part of Abilene’s stormwater management plan is to allow water to flow down certain secondary streets, and these small holding areas are crucial to slowing the water down enough to prevent flooding.

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Detention pond after a rainstorm

You might be surprised that there are so many of these ponds scattered across Abilene, since there are so few bodies of water. Many of these ponds are just a few feet deep and spend most of the year as open grassy areas. You may have seen children playing in a detention pond and didn’t realize it was a pond! These ponds provide a place for water to collect during heavy rains to prevent flooding and they slow the flood water down, allowing some trash and debris to fall out of the water before it gets to the lake.

And there is one source of your drinking water. Next week we’ll take a look at another source of water.

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Grab a paddle

A while back I posted an explanation of where and how much it would need to rain in order to fill up Fort Phantom lake. Not accounting for absorption or detention in ponds and other low lying areas it would take a 2.6 inch rain on the entire watershed to fill up the lake, according to my previous calculations. Well, currently Cedar, Elm and Catclaw creeks are out of their banks in places. The following map shows a few rainfall totals for places in the Fort Phantom watershed

7_7Rain

Without data for the western edge of the watershed, it is impossible for me to offer a good estimate of exactly how much water will flow to Fort Phantom lake; however, judging from how little Lake Abilene has risen, I think it is safe to say that portion of the watershed will not contribute as much water to Fort Phantom as the eastern half. As of today (July 7th) the lake is at 45.3%, but click on the link to see the current lake level. Get ready to see a change in the lake level in as the week goes on! And check back here later this week to read about why it can take so long between a rainfall event and a change in the lake level.

Goldilocks wouldn’t like Texas

What a difference a week made for some places in Texas! Parts of Texas experienced massive flooding which resulted in deaths, bridges lost, and at least one dam failure. Many reservoirs experienced dramatic changes in water level, with some becoming full nearly overnight. Possum Kingdom is full and was releasing water into the Brazos, and evacuations are occurring downstream. For the first time since June 2010, the USDA Drought Monitor does not show any severe drought in Texas (and it should be noted that time in 2010 without severe drought lasted only six months.) We have been free of severe drought only 26 months spread out over the last 11 years, and completely free of drought only three months during that same period.

Despite all of this rain and despite the drought relief, for many Texans, it is the same story as last week: The ground is damp, but the lakes are dry. Here is an updated map comparing the new drought index with current lake levels:

The largest red circles represent lakes that are below 25% of capacity, the medium dots are lakes that are between 25 and 50% full, and the smallest dots are lakes which are between 40 and 75%.

A comparison between the USDA Drought Index and Texas Lake Levels.

A comparison between the USDA Drought Index and Texas Lake Levels.

As you can see, while those along the Brazos are wet, people along the upper reaches of the Colorado River are still dry, even if the drought index has shrunken. With another month of spring left, hopefully things will continue to change for those of us in the dry areas; however, in this area the el niño effect often wanes during the summer before returning during winter. In other words, we may have a wet summer in the western portion of the state, or we may not.

Here is a comparison of May rainfall totals for a few select stations across the drought area. For ease of data collection these are mostly airport locations, so the totals may vary slightly from nearby cities. Notice that other than a few large outliers (Austin at nearly 17 inches of rain for example) that some of the dry areas aren’t that far behind some of the wetter areas. This goes back to my previous post about watersheds: it takes rain in a certain area to influence lake levels.

Rainfall totals so far this May (inches).

Rainfall totals so far this May (inches).

Certainly, we are better off today than we were this time last year, but now is not the time to abandon water conservation. In terms of water it seems the state has very few places that Goldilocks would consider just right.

Next week I begin a three part series on how one city in Texas obtains its drinking water. If you enjoyed this post, please surf over to the Instante Mense facebook page and like it.