These features form sills separating Bass Basin from the adjacent ocean basins. The Delaware Basin is the most important of these three basins. Fringing stands of tall vegetation by water basins and rivers may include helophytes. Pollution in stormwater runoff collects in retention basins. Geomorphologists and hydrologists often view streams as being part of drainage basins. Short duration precipitation is more significant to flooding within small drainage basins. Within these primary drainage basins are approximately 60 smaller basins, or subwatersheds. Evapotranspiration is a significant water loss from drainage basins. This dense water then flows into the ocean basins. Storm drains may discharge into man-made excavations known as recharge basins or retention ponds. They have a geographical link with regional boundaries being based largely on drainage basins. Physical process models of complete drainage basins are even more complex. The EAR also cuts through old sedimentary rocks deposited in ancient basins. There are many river basins and gentle slopes as well. The majority of these lavas erupted or flowed into the depressions associated with impact basins.