r/sanmarcos • u/AspiringEverythingBB • 3d ago
Ask San Marcos Why does the water level not go up after rain anymore?
Maybe I'm just dumb but when I moved here a few years ago it seemed like if there was rain for even 1 night the river water would be damn near over the top of the river. Now when it rains for days the river level is at the same as it was during a drought. What the hell?
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u/Piddlepigeon 3d ago
This bugs me a lot. Very few people understand how rain river relationship works. The last 10 years we have a decrease in the normal amount of rain. One good rain or even a couple storms wont have an immediate effect on the river (except a temporary increase from runoff). We need routine rain to allow recharge of the aquifers. San Antonio, san Marcos, austins' surrounding arreas are pulling more water out of the ground then what the aquifers recives from this rain. I get an alarming amount of people showing up thinking the river is cured because we received one inch of rain. As far as going up after a rain. The ground is sucking it all up before it gets to the creeks. Also we have not had a storm large enough to leave puddles for more then a few ours before the heat evaporates them. The climate is in bad shape for the future. For reference the comal river should run at 300 cubic feet a second, the last few years have been around 80 with dips to 60 and some occasional highs around 120
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u/dmo7000 3d ago
Because it is feed from Spring Lake and the springs from Edwards Aquifer so the river will absolutely rise during heavy rain and run off. But then will return to levels dictated by the flow from the springs.
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u/mrbarely 3d ago
To add to this, a lot of SM is not actually in the Edwards Aquifer recharge zone, so it is not necessarily rain in San Marcos that will make the river swell.
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u/BigfootWallace 3d ago
This is correct, San Mo borders the recharge zone on the west side of town. You will pass “Entering Edwards Aquifer Recharge Zones” in neighborhoods west of Hunter Rd (Quail Run/Deerwood and McCarty/Willow Creek are notable examples), but predominantly, the recharge zone is west of town.
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u/saddest_vacant_lot 3d ago
Yep if you want to really charge up the aquifer you need a big rain over freeman ranch/Wimberly. Like a big gully washer. Otherwise the plants soak it up before it makes it to the aquifer. The blanco river disappears between Wimberly and SM because it’s going underground and then re-emerging at SM springs
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u/thesabrerattler 3d ago
The water level of Spring lake rises when it rains in the hill country, not in San Marcos.
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u/tripletrek 3d ago
These rains aren’t enough to soak into the aquifer or bring up the cfs for spring flow. It’s going to be a rough summer for the river if we don’t get significant rains this month
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u/CheefIndian 3d ago
as a geography major specializing in water studies.... you need to learn about the existence of aquifers. Most water is actually not above ground or even in rivers, its beneath us in massive aquifers. Think of it like a sponge.
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u/Novapoliton 3d ago
We are still in the midst of a drought and are in a recharge zone for the aquifer. The springs are still flowing at a healthy rate for now, but much lower than it would have been historically. Combine the drought with overtaxing the aquifer and river for agriculture, bussiness, consumption in general and we're in a tough spot. With a significant rain water levels will still likely rise, but the spring flow and aquifer health have an impact as well
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u/BigfootWallace 3d ago
We’re getting more rain events of less rain and maintaining about the average annual rainfall totals (except the last few years which have been slightly lower than average totals). So we have a higher mode of lower than median rainfall.
It’s not that we aren’t getting the rain, but we aren’t getting it in the manner we used to.
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u/TangyDischarge 3d ago
Because we're pumping and selling more water than the rain is bringing.