WEATHER BLOG: Why Watershed Levels Are Lower Than You Might Think

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Most people would assume that our aquifers simply fill up after rain. But that doesn't happen.

Corpus Christie, Texas. Many people think that the rains in August and September will make our tanks nearly full or fuller than they really are.

Here are our current watershed figures: Throttle Canyon is 34.4% full, Lake Corpus Christi is 88.7% full, and the combined watershed level is 49.5%.

We get a lot of questions about how it's possible that Lake Corpus Christi is close to capacity, but overall water levels don't seem to reflect this. To answer why, we need to do some math. It's not bad, I swear.

Corpus Christi Lake has a capacity of 256,062 acre*ft, while Chok Canyon has a capacity of 662,820 acre*ft, 2.5 times the volume. The reservoir (sum of two) is 918,882 acre*ft.

Since they are not equal in volume, this is not a 50-50 split. We cannot average the two to find the water level.

By dividing the power of each contributor by the total power, we find out how much each source contributed. This means that Lake Corpus Christi provides 27.9% of the groundwater, while Choc Canyon provides 72.1%.

So if Lake Corpus Christi (LCC) is 100% full and Choke Canyon is 50% full, our reservoir will not be 75% full (50% LCC + 25% Choke Canyon). Instead, we must use percentages to get the actual weighted average, which will give us 63.9 percent of the total water.

We use our original numbers today. Lake Corpus Christi is 88.7% full and Chok Canyon is 34.4%.

Lake Corpus Christi = 27.9% x 88.7% = 24.8% in the watershed Hawk Canyon = 72.1% x 34.4% = 24.7% in the watershed

Added together, we get 49.5%, which is the current level of the combined lake. See, it's not that hard!