Running in pool to allow young females (14-16 yrs old) to train and avoid pounding of running of track/roads

pool running is great for the purpose you seek. Have them build up the time they can do, starting with 10 minutes or so. I was once told not to do more than 45 minutes or else it turns into a strength workout. You can mimic running workouts by time: eg: if you want to do intervals go by time (eg: 8 x 90 seconds instead of doing 400s on the track) A belt can be helpful so that you don't have to worry about staying afloat but I learned without one and like going without for developing core strength. Different body types benefit differently from the pool running: weak in the quads may struggle at first but in the long run grow stronger. A girl with no muscles may find not have as much resistance in the water as she lifts her legs and not be able to get as much of a workout as someone with more muscle mass to move through the water (I am told that going in with a pair of old running shoes gives more resistance but haven't tried it myself)