Lucky you. there is a shortage of bees and these mining bees are very valuable. They do not sting by the way.

Please don't try to get rid of them as they are very valuable pollinators and do no harm whatsoever. The clouds of them are probably associated with mating behaviour later in the season.
Read what is said about them at the University of Rhode Island website:

"Mining bees, or digger bees, (familys Andrenidae & Anthophoridae) nest in burrows in the ground. Unlike the honey bee, mining bees are "solitary" bees. They do not form long-lived colonies, nor do they live inside a single, well-defended nest controlled by one queen bee. Instead, each mining bee female usually digs her own individual burrow to rear her own young. Large numbers of these bees may nest near one another if soil conditions are suitable.

Mining bees are not aggressive and seldom, if ever, sting. The presence of numerous bees flying close to the ground, however, may constitute a nuisance for some people. Sometimes large numbers of males will fly about the same spot for several days in a mating display.

Mining bees range in size from about the size of honey bees to much smaller. The larger bees are furry and usually darker in color than honey bees. Some are brightly striped, while others are a shiny metallic green. Mining bee burrows may be located wherever there is exposed soil and good drainage. They are frequently found nesting in banks, such as along road cuts or any type of excavation, but may also be in level ground as well. The holes are about 6 mm (1/4 inch) or less in diameter. They are sometimes surrounded by a small mound of soil that the bee has brought up to the surface. Burrow structure varies according to species, but often there is a vertical tunnel with smaller side tunnels that terminate in a single cell.

The female mining bee stocks each cell with pollen and nectar she collects from flowers and then deposits an egg on the food mass. The larva hatches and consumes the stored pollen and nectar. When mature, it becomes a pupa, or resting stage, and finally becomes an adult bee. The adult bees overwinter below ground in the burrow site. During the next spring or early summer the adults emerge, mate, and the females begin burrow excavation. Mining bee populations can fluctuate dramatically from one season to the next."

End of quote

Wish we had a colony in our garden!

Many thanks for your info re miner bees. I now have a better understanding of them