Tag: runoff

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Let’s “Save it, Don’t Pave it!”

Recently, I saw a phrase on a t-shirt: Save it, Don’t Pave it! (https://aquiferalliance.org). The Aquifer Alliance is attempting to raise awareness of how detrimental concrete can be to the Edwards Aquifer.

We here in Gillespie County need your help with our own aquifer, the Ellenburger Aquifer,  which provides most of the drinking water for Gillespie County. It is in trouble. Recently, a Hill Country Critical Groundwater Depletion Area 1 was declared for the Ellenburger. The drought and normal usage of water has reduced the aquifer’s levels to a point where we must all take efforts to cutback our water usage.

But it rained! And we expect more!! But if there is one thing we all know, the weather is not consistent. Just when you think rain is coming, it doesn’t. Just when you think it will be cooler, it won’t be. The only thing we know with certainty about the weather seems to be that it seems to have a mind of its own. This means we should all consider how best to make cutbacks to our water usage permanent.

One way is to not put down concrete. For years, we have been paving parking lots, walkways and driveways using caliche topped with crushed granite. This construction allows for rainwater to soak into the ground. When water soaks into the ground, it has a much better chance of recharging our aquifer. Concrete, on the other hand, just helps to create runoff which is, by definition, pollution.

Water that falls on lawns tends to run off to roads carrying excess fertilizer and even dog poo. The runoff hits concrete roads and picks up oils, residue from tires, dirt, debris, trash and more. Short or light rains do not always push this runoff down to the river but a frog floater (colloquial term for a whole lot of rain at one time) will. When a lot of water from a heavy rain hits the seasonal creek beds, everything, including the now concentrated pollution, goes downstream to the Pedernales River.

I watch the river and see people fishing, wading, swimming and kayaking in it. Even when you think the River is too low for these activities, folks find a low water crossing and they play in the Pedernales…and, if we’ve had a recent frog floater, they unknowingly play in the polluted water.

More importantly, when you understand that all water in the Hill Country is connected–streams, creeks, river, springs and aquifers, then you know that any pollution anywhere in the Pedernales Watershed is too much. (See “The Journey of Groundwater” https://youtu.be/52Ln-LBr5ZU)

We all need to conserve water in any and every way that we are able for the benefit of all. If you are building a new home or business or upgrading your own property, please put in a permeable surface for your parking areas, walkways and patios. Save it, Don’t pave it!

Deborah Youngblood
Pedernales River Alliance
https://pedernalesriveralliance.org

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What’s a Watershed?

A watershed is a system, land that drains rain and melting snow to creeks and then rivers and eventually, the ocean. Most of us here in Gillespie County live in the Pedernales River Watershed. Near the headwaters of the Pedernales are two areas of land where water drains to a creek and each land area draining to each creek is a watershed. One creek is called the Klein Branch and the other is called the Banta Branch. These two creeks join together and become the Pedernales River. As the Pedernales River flows eastward, there are many more creeks that feed into it. Each of these creeks is a sub-watershed of the Pedernales River Watershed.

The Pedernales River Watershed extends into Blanco County and then on to Travis County, where you will find the mouth of the river at Lake Travis which was formed by damming the Colorado River. The Pedernales River is a sub-watershed of the Colorado River.

Now, pull out a map and trace along the route of the Pedernales River and you can easily see how many communities depend upon this river for water. Ultimately, even Austin depends, in part, upon our River as does a state park, an LCRA park, a national park and numerous county and private parks. These are very good reasons for keeping our River clean.

The kinds of things that can adversely affect our River’s water quality include runoff, littering, excess fertilizer, and malfunctioning sewage systems.

Fast flow of water draining to Grape Creek
Fast flow of water draining to Grape Creek

Runoff includes sediment. Who knew dirt could be a form of pollution? Weird but true. When dirt is washed into the river from large construction sites, it’s just too much of a good thing.

Littering is an easily preventable source of pollution – just don’t do it! And even if you did not, go ahead and pick it up anyway. That’s called being a good citizen. Litter can get into drainage systems and ultimately affect the health of the river.

 

Excess fertilizer can wash out of your yard, into the drainage system, into the creek and on to the river. It can wash out of farms, too. This is called non-point pollution because we cannot always pinpoint where it comes from but you can be sure that when the river is choked with thick, green algae, fertilizer might just be the source. The solution? Plant native plants that love the sandy loam and clay soil around here and you won’t have to fertilize. Put in native grasses instead of turf grasses that need to be fertilized and watered to be pretty.

Baron's Creek below the Sewage Treatment Facility Outfall
Baron’s Creek below the Sewage Treatment Facility Outfall

A big source of pollution is malfunctioning sewage systems. Reality check, we need our septic tanks! But we CAN make sure they are working correctly. If the grass over your septic tank and drain field is nice and green, your septic system may be leaking. A septic system’s drain field that is working properly usually looks pretty rough. Investigate to find out what is making your grass so unexpectedly and beautifully green.

Another source of pollution comes from treated wastewater. Sewage treatment facilities clean sewage and then release the cleaned water into creeks and rivers. The only problem with that is a huge problem: the water contains phospates and nitrogen, the same nutrients in fertilizer. Algae love it and a creek of river contaminated with treated wastewater will become clogged with green algae in short order. The correction to this is to clean wastewater to make it potable or to use the treated wastewater to water golf courses, lawns, and other non-food sources.

Bottom line, the Pedernales River watershed is a system that includes you. Doing your part to keep the Pedernales River Watershed clean will help keep our River clean.

 

 

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Runoff

The Water-Cycle
The Water Cycle

When it rains,  runoff is the water that does not soak into the ground; it is the water that runs downhill, into the manmade drainage systems. It is the water that runs to the creeks and rivers to the oceans. It is the water that is not soaked into the earth, and does not recharge the aquifer. Runoff tends to move rapidly carrying with it trash, sediment and debris.

Surface runoff enters the downhill flow almost immediately flowing to the surface waterways. Sub-surface runoff leaches into the soil and moves laterally without joining the water table, to the stream, rivers or ocean is known as sub-surface runoff. Rainfall which infiltrates into the soil and meets the water table and flows to the streams is very slow is referred to as delayed runoff.

Runoff is generated as long as the rainfall intensity exceeds the actual infiltration capacity of the soil. The soil, like a sponge, can only hold so much. Runoff stops when the rate of rainfall drops below the actual rate of infiltration. In other words, when the rain slows down to a rate that is slower than the absorption rate of the soil, runoff drops.

Factors Affecting runoff rate include

Climate factors:

  1. Types of Precipitation: It has great effect on the runoff. When it rains runoff starts immediately. When it snows, the snow does not immediately result in surface runoff.
  2. Rainfall Intensity: If the rain comes down faster than the soil can absorb it, runoff happens. If the rain comes down slowly, runoff happens when the soil cannot absorb any more water. If it rains a lot then a lot of runoff is generated.
  3. Duration of Rainfall: If the rain continues over a longer period of time, runoff happens because the soil cannot absorb all of the rain.
  4. Rainfall Distribution: Runoff from a watershed depends on where the rain falls. If rain falls near the outlet of watershed, runoff will be more.
  5. Direction of Prevailing Wind: If the direction of prevailing wind is the same direction as the drainage system, it results in peak low. A storm moving in the direction of stream slope produce a higher peak in shorter period of time than a storm moving in opposite direction.
  6. Other Climate Factors: Other factors such as temperature wind velocity, relative humidity, annual rainfall etc. affect the water losses from watershed area.

Physiographical Factors:

  1. Size of Watershed: A large watershed takes longer to drain than smaller watershed and vice-versa.
  2.  Shape of Watershed: Shape of watershed is generally expressed by the term “form factor” and “compactness coefficient”. Form Factor = Ratio of average width to axial length of watershed. Compactness Coefficient: Ratio off perimeter of watershed to circumference of circle whose area is equal to area of watershed. Two types of shape:
    1. Fan shape – tends to produce higher runoff early
    2. Fern shape – tends to produced less runoff
  3.  Slope of Watershed: The slope controls the time of overland flow and time of concentration of rainfall. Slopping watersheds result in greater runoff due to greater runoff velocity and vice-versa.
  4.  Orientation of Watershed: This affects the evaporation and transpiration losses. The north or south orientation, affects the time of melting of collected snow.
  5.  Land Use: Land use and land management practices have great effect on the runoff yield. An area with forest cover or thick layer of mulch of leaves and grasses contribute less runoff because water is absorbed more into soil.
  6.  Soil moisture: Magnitude of runoff yield depends upon the initial moisture present in soil at the time of rainfall. If the rain occurs after along dry spell then infiltration rate is greater, creating less runoff.
  7.  Soil type: In filtration rates vary with type of soil.
  8.  Topographic characteristics: Undulating land has greater runoff than flat land.
  9.  Drainage Density: The longer and wider a watershed area the greater the runoff
  10.  Storage Characteristics:
    1. Depressions
    2. Ponds, lakes and pools
    3. Stream
    4. Channels
    5. Check dams in gullies
    6. Upstream reservoirs or tanks
    7. Ground water storage in deposits/aquifers

Runoff is part of the water cycle. It cannot be eliminated. We can slow it down so that the water can soak into the soil, reduce erosion and sediment displacement.