Nurse roots?

Imagine a Los Angelean suburban back yard about 3 miles from the sea. Sod was laid 30 year ago, but irrigation was stopped a decade ago. A mature liquid amber, a strawberry tree and some older shrubs survive. Now we are transitioning from dead lawn/non-native weeds to native plants. The soil is mostly compacted clay and the whole property is on a slight slope. We want to keep rainwater runoff and moisture from gutters on the soil, but swales are hard to dig because tree roots crisscross near the surface. Instead of digging down, can we do shallow, wide swales and make berms of the displaced earth mixed with fallen branches and leaves?

We’ll be adding a chip drop as soon as we’ve set up the swales. We are currently watering the soil and weeding out the sprouting grasses. We’ve planted a test Ceanothus, native iris, CA sunflower. Thoughts?