Make Riven's Q cooldown start after the third Q
Right now the Cooldown is 13 seconds but it might as well be 5-6 seconds because she can use her first Q, then zone you ever 3 or 4 seconds with another Q, stun you, disengage, and then her Q is back up again. This gives her way too much lane control. Not to mention that fact that at 40% CDR Q's cooldown is 7.8 seconds, meaning if she waits the full time between Q's her Q has NO cooldown
You can even reduce the CD from 13 to 10 to compensate, at least that way she has a window of vulnerability
You made this change to Jayce's hypercharge so he couldn't abuse his damage, now do it to riven to tone down her oppressive laning