As mentioned, the Boron 3G will use more battery power than the LTE version.
However, since you've already mentioned using an external timer, this wont impact you as much.
The Self Discharge for Li-On Cells is going to hurt you for a 1-year deployment without recharge.
That can be easily overcome with a tiny Solar Panel, or switch to Primary Batteries.
Here's a trial I performed with both examples (Li-Po +Solar & Primaries Only) using a TPL5111 and Boron LTE.
Summary of Results:
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The 0.5 watt Solar Panel maintained the Li-Po ~90% Charge with a 5 minute Cycle interval (Startup, Cellular Connection & Publish). SoC ranges from 93% (daytime) to 85% (early morning before sunrise)
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The 3xAA performed 10,000 Cycles before depleting the batteries (equals ~1 year @ 1 hour Cycle interval).
The downside to using the Enable Pin is the Boron performs a full handshake for each cycle.
(Hourly cycle interval might cost you $1 per month over the minimum Cellular Bill.)
The benefit is you don't need to wait for Sleep Modes, or depend on them.
Since your project is outdoors, I would add a tiny Solar Panel.
Keep in mind a ultrasonic sensor will need to have a measurement range much larger than your expected water level range. It gets mounted to a bridge that's a good bit higher than the max water level expected. IE, your 3 meter range of water may require a 10 meter sensor depending on it's mounting location. That's the reason I'm going with the 35' range MaxBotix sensor I mentioned.