Dear Pam:
Anytime roots are lost, a lose of water into the canopy will happen. Be sure the plants are well watered just before the sidewalk construction and immediately afterwards. the farther the root pruning cuts are from the trunk the less impact. Next season plan on feeding the evergreens and be sure to keep up with the water next season at least so the plants can rebuild the roots on the affected side.
Hope this is helpful,
Richard