Great question! And a complicated one!

Beaches form as the result of waves or water currents moving and depositing sand and other loose sediments along the shoreline. Beach erosion happens by the same process, but instead of sand being deposited it is carried offshore. Therefore, the movement of ocean water is what causes the sand transportation and thus beach formation along the coasts. And the waters in the ocean are always moving! That water movement is due to a variety of factors including, Earth's rotation, gravity, wind patterns, temperature and salinity (saltiness) of the water, the shape of the sea floor, and the presence of land masses (such as the Channel Islands).

The Goleta coastline happens to be where several ocean currents converge, or meet and flow together. The California Current flows south, bringing cold Alaskan waters down along the coast. The Southern California Counter-current brings warm waters up the coast from Baja California. There is also warm, saline (or salty) waters brought into the coast from the central North Pacific Ocean from regular tide movements. Off of our coastline, there is also coastal upwelling of nutrient rich waters from the deep ocean. Upwelling is caused by the blowing of wind along the coast, causing surface waters to push away from the coast, which allows the cold, nutrient-rich waters from the bottom of the ocean flow up and replace the surface waters being pushed out to sea. This combination of currents forms one of the most biologically productive ecosystems along the U.S. coastlines. And as these water bodies converge off the coast, they wrap back around to the south (imagine the water converging near Point Conception and flowing around counter-clockwise back into the Los Angeles coastline) due to the coastline shape. As they converge, both the south-flowing and north-flowing waters split and flow around the Channel Islands. This causes a variety of differences in the ocean movements within the Santa Barbara Channel, which does affect the Goleta coastline. I am not a coastal geology expert, so that is about all I can say. But I do know that the Channel is relatively protected compared to the oceanward side of the Channel Islands, meaning that the islands act as a wave blocker. Without the Islands, our shoreline may have less sandy beaches because the waves (especially storm waves) would wash away all the sand.

An equally important factor to consider when thinking about why we have beaches and where they form, is human development. Humans are huge factors of beach erosion by changing the coastline or building artificial barriers to the natural ocean erosion. For example, the airport in Goleta is located where there used to be a swampy lagoon , similar to the Devereux Slough that was recently restored near the Ellwood Bluffs. When humans closed off the lagoon, they also closed off a sediment source into the oceans.

Another example is the break wall in the Santa Barbara harbor. The seawall protects the coast from erosion, but it also disrupts the natural transportation of sediments along the coast. The end result is that it causes increased erosion down drift from the sea wall, meaning it causes beaches to be stripped of their sand. To counter the effects of sea walls, several beaches along the Goleta coastline have massive amounts of sand dumped onto them. You may have seen Goleta Beach under construction in the past as every year engineers try to add large stone blocks along the coast, that are then buried under sand, to prevent erosion.