Planning a swale

This section of the front yard is currently a buffer of plants along the road. I am planning on creating a swale here instead. 12 ft wide at the widest and 4 feet wide at its narrowest. I am currently making calculations on the appropriate depth and appropriate berm height. Also planning the vegetation to go in the swale and on the berm. Trees and shrubs will go on the berm (ginkgo tree, pineapple guava) and annuals and perennials go in the swale (italian parsley, daikon, bell beans, chard (biennial), valerian, thyme, lavender and more). The plants currently along the road (lavender, lavatera) will be moved to suitable sections of the swale. These plants are drought tolerant plants. This swale will help deal with the deluge of water runoff from the road during the rainy season and focus that to a target tree (ginkgo), which will offer shade from the afternoon sun. The swale will replace a section of lawn with a wider diversity of plants, create visual interest from the road side and the house side, and encourage diversity of insect and bird life.
I'll start digging as soon as the temperature cools to a more reasonable range (80s).