Has anyone considered a rain garden? We have one at the garden center, but it is mostly full of weeds. It was actually built on higher ground. The water actually collects in the herb garden and since it can stay wet awhile, I had to brick over one section and put some of the plants in large planters instead. I do like the idea of building a catchment basin in the low spot, but since my low spot in the yard is not where it would be convenient to have a pond. I have tried to actually dig a channel from my back to the front of my yard just to keep the patio from flooding when it rains hard.
I remember a program once in the Mideast about how land is farmed in the desert. They need a lot of land to collect water. The land is contoured and the field is actually planted in the low spot where the water collects. Apparently this is the way the land has been farmed for centuries. I remember they called the area Fedans instead of acres or hectares.
I have two rain barrels. Right now they are overflowing. I have a third barrel that still needs to be set up and I want to get a fourth. I have never actually emptied my rain barrels, but I use the water in a five gallon bucket and dunk my orchids in it to water it instead of pouring the water over the top. 10 gallons of water will go a long way that way for at least 50 orchids. I use about 15 gallons of water for my potted roses, bamboo, croton, gardenia, and Ohia Lehua. I only water them every 4 days if I remember. Sometimes I go too long and they start to wilt. Good thing I have them by the front door, so I have been able to rescue them before they die. I may have to put them into bigger pots so they will dry out slower.
Happy gardening in Hawaii. Gardens are where people grow.