It's not about time or miles exclusively.

You could go out and stroll for 6 or 7 hours with nothing and you wouldn't exhaust your glycogen simply because at that level of exertion, you'll be burning mostly fat.  You could jog for 30 miles and not exhaust your glycogen if you jogged easily enough.

As you sit there reading this, your fuel is coming almost exclusively from fat.  Your body burns fat preferentially because even those with very low body fat percentages will have something like 35,000-50,000 calories of fat in their bodies as compared to maybe 1,500-2,000 calories of glycogen.  As the intensity of your exercise increases, so does the percentage of your energy coming from glycogen.  At some point, nearly all of your energy will be coming from glycogen.  However, if you run so intensely that nearly all of your energy comes from glycogen, you probably won't be able to exhaust your glycogen supplies.  Why?  Because you'll be over your lactate threshold and that will cause you to slow long before you run out of glycogen.  Thus, you only run out of glycogen in events that last a while and in which you are running at a fair degree of intensity.  A marathon is the perfect distance to cause you to crap out.  Bear in mind that elite runners will be running a marathon somewhere around 80-85% of VO2max.  Most of us will be closer to 70-75%.  My guess is that people who are running slower than 11:00 or 12:00 per mile are closer to 60% and thus in no danger of glycogen exhaustion during a half marathon.

Having said that, there are enormous individual variations in glycogen storage.  As with everything, there are genetic differences.  Beyond that, a trained athlete may be able to store twice as much glycogen as an untrained person and people who have only been running less than a year would fall into the "untrained" category even if they do have enough endurance to finish a half marathon.  It is possible, even at their 60% VO2max exertion level, that they could run out of glycogen.  I have my doubts but it is possible.

One last consideration.  Many people take in way, way more than they need in a half marathon.  The problem with this is that your body preferentially shuts down the blood flow to your digestive system in favor of your exercising muscles when you race.  Take a bunch of gels and it is entirely possible that you'll experience severe gastric distress and I can promise you that the severe gastric distress will slow you down much, much more than some perceived fatigue.

...Hydration in a half-marathon depends mostly on the weather.

Hydration will likely depend on the duration of the race more so than the distance - plus the weather and probably some other things. Not everyone is doing their HM in 1:35. Some of our local ones with hills may take over 3 hrs, even for the fast folks. And a newer (new to running) or older (age) runner, even on a fast course, may easily be out there over 2 hrs.

oops - should have read the rest of the thread first to see this was already addressed.

I think it's most about time and not miles.

Seems that more runners think in terms of miles though rather than time.  Since the timing clock is not always found on the course but rather the mile markers are, people know that they will cover a mile in X minutes so a 10 minute/mile racer knows they will hit the 45 minute mark somewhere between mile marker 4 and 5 so they plan to look for the aide station around that point to take a gel going in to the aide station.  I'd rather have a plan to take a gel every 5 miles at 5, 10, 15, etc than be thinking in my head alright 45 minutes, 1:30, 2:15 oh wait was the last gel at 1:20 or 1:40.

Keep it simple.  Run more, think less.

Personally I think 2 GUs for a half is excessive but stick with the way you have been training.  As for taking a GU every 45 minutes well that advise comes from the makers of the gels who's master plan is to sell more gels.  You might find you can delay taking the first and not need the second gel.  I do not recommend taking a gel and washing it down with G-ade as that will likely set off a sugar bomb in your stomach.

I am guessing that you are close to race day so if that is the case now is not the time to be experimenting but rather fine tuning the race plan.  After the race make your experimental refinements based on how the race went.

I think your plan is good as a starting point-- you have (at least) one long run left so you can try it out to some extent in training.  It's always different at race pace but you should be able to get some idea of what your stomach will and won't tolerate.

I take two GUs during a goal HM and I'm faster than Kristin, so to me, the plan looks OK.  I wouldn't do Gatorade if I'm doing GU, though, and I would stick with water during those miles.  But I don't think it will hurt your stomach so long as you keep drinking water.

+1

another thing some people don't understand is that you have to drink water with GUs for it to work.

If you are carrying a hand held or *gulp* a fuel belt, dissolve GU in water and put it in your bottle instead of carrying gels.

 

One more thing. The beverage Venomized is suggesting with his avatar might not be the way to go prior to a race.

However, I can say from my Boston experience that beer during a race ain't half bad.