Northern Guam geospatial information server
"Plumbing" of the NGLA
Recharge involves fresh water making its way from the land surface (where it arrives as rain) down through the unsaturated bedrock all the way to the water table. Some of this water percolates through small and poorly connected pores in the rock. Water subject to this vadose percolation can takes months to years to reach the water table. However, a lot of water flows down via rapid pathways that extend from solution sinkholes at the land surface and continue via widened fractures and natural shafts downward to the water table. Water involved in vadose fast flow reaches the water table in minutes to hours. Many solution sinkholes that lead to preferential pathways for water in the subsurface have been developed as ponding basins as northern Guam has been subject to extensive urban development.