My yard is on the downhill side of a street with no curbs, so a lot of water comes into my garden every time it rains. One solution would be to put in a curb but that will just run the water down to the neighbor's garage which is not a nice thing to do, and rainwater can be a good thing as long as I can control where it ends up. An alternative solution is to try to direct and absorb the water using swales and raingardens. Swales are just shallow ditches that are strategically placed where water needs to be sent from one place to another. To absorb the most water, dig your swale on contour, parallel to the slope, placing the displaced soil on the lower side of the ditch to form a berm.
At the top of my yard, I have dug a shallow ditch parallel to the slope and planted sedges in it. The sedge loves the water that gets trapped in the swale and helps to slow the flow as it comes into the garden. Since one swale didn't seem to catch all the water, I dug three more at about 5 foot intervals parallel down the slope. The top one fills up and flows into the next. The ditches slow the flow to prevent erosion and hold a little water absorbing it into the soil. The top swale also catches a lot of trash that runs off the street, so I go out and pick that up after every rain. Below my swales my garden is constricted as it goes around my porch, so I built a series of three small rain gardens to catch, infiltrate, and direct the water as it continues down the hill. We are about halfway down the garden now, so the water has been significantly slowed and during a short rain it has been trapped to absorb into the soil.
However, in the spring there is still more water coming off the street and all my swales and rain gardens are overflowing so I made two more swales to bring the water across away from the porch and into another two larger rain gardens. This spring all this was still not enough to catch all the water, but I still call this success. My garden paths and patio are above water and not washed out. The rain goes from one part of the garden to another without washing out all my plants. I have trapped and absorbed a significant amount of rain to sustain my native plants through the summer. I am putting the rain to work for me, and all of my contouring has added character to my garden.
Plants that grow well in swales are:
Palm sedge, Carex muskingumensis
Golden groundsel, Packera obovata
Christmas fern, Polystichum acrostichoides
American beak grain, Diarrhena obovata
Fox Sedge, Carex vulpinoidea
Common spikerush, Eleocharis palustris
Lizard's tail, Saururus cernuus
Soft rush, Juncus effusus
Cardinal flower, Lobelia cardinalis
Wild strawberry, Fragaria virginiana