Hi Caitlin, one very effective solution to this problem would be to use a waypoint capable drone. These use GPS coordinates to return to the same point in space and repeat the same photograph (or video) over and over. This could be done over days, weeks, months or years as long as you keep the waypoint stored on the drone. Multiple waypoints can be used to take several shots from different positions. This also has the advantage of taking photographs from anything up to 400ft up which would give a much better overall view of a flood or management scheme. Positioning accuracy would typically be around +/- 1.5m horizontally and +/- 0.5m vertically. The cameras on a good quality drone would also be vastly better than a mobile phone and are stabilised so they don’t blur the photographs and video isn’t jumpy.
There are a number of applications out there that can stitch photographs like this together to create timelapse effects. The software that comes with DJI drones can also produce numerous other effects such as slow-motion video, panoramic photographs, Point-of-interest shots (e.g. moving the camera around while keeping the same spot in the centre of the frame to give different views of it) etc.