Low water production

I have 4 sandpoints at about 23' all connected to one pipe equal distance apart. I have a 1 hp Flotec pump and the size of the pipe is 1 1/4. For the first 5 mins. I get about 15 gpm then after that production slides off to about 6 gpm. What is the problem do you think? I need to have at least 14 gpm for lawn watering. What is the usual time alotted for watering lawns?
Thanks
Bob

Your wells are only supplying that much water. You may need to put in 4 more to almost double the production. Where is the water level in these wells?

There is no usual time to water a lawn, it depends on how much water is needed and how much is applied.

bob...