IT IS STRONGLY RECOMMENDED THAT YOU DON'T DRAIN WATER FROM YOUR POOL DURING HEAVY RAINS AND FLOODING CONDITIONS.
Lowering your pool's water level will not have any related impact on the height of the water level in your backyard. Your backyard has moving water flowing through it and even taking 15,000 gallons of water from it will have not impact on the water flowing into your backyard behind it.
The amount of water you remove is extremely small compared to the amount of rushing water that is associated with flooding conditions in your backyard and property.
Any amount of water you remove from your pool will be filled back up within moments when your backyard breaches over your pools edge.
Pool pumps also do not move enough water to drain water fast enough to lower your backyard water level.
IMPORTANT SAFETY REMINDER:
DO NOT EVER GO OUT IN THE RAIN OR FLOODING CONDITIONS TO TURN YOUR PUMPS ON OR OFF. USE YOUR MAIN BREAKERS OR INDOOR CONTROLLERS TO TURN EQUIPMENT OFF OR ON.
POOL PUMPS ARE IN DIRECT CONTACT WITH THE VERY WET GROUND AND THE ELECTRICITY IS BONDED TO THE GROUND BACK TOWARD THE POOL.
ANY WATER THAT GETS INTO THE MOTOR HOUSING CAN BE VERY FATAL TO ANYONE AROUND THE EQUIPMENT.
* Remember to keep the sides of your house/gates open so that backyard water can easily flow to the front.