Aren't logs and such also used to create waves on rapids rides? Although they can be dangerous in the event of an emergency pump shutdown.
Logs are bolted to the channel base so as to disrupt the flow of water going over them, creating 'rapids' in the process. They are not dangerous in the event of an emergency shutdown as long as no more boats are sent around the circuit after the pumps stop. The boats flow at the same pace as the water, so should the pumps fail, the boats currently on the circuit will be fine. The water does not travel faster than the boats, so the water level could not drop for boats already on the circuit should the pumps be shut off.
The wavemakers, as Intamin calls them, are machines with a large sheet of steel pivoted at the top, connected to a crank, gearbox, and then motor. The crank turns the rotational motion of the motor into a back-and-forth movement, which then swings the steel sheet back and forth. This is submerged in the water, so it moves a large volume of water back and forth, creating large waves that are not fixed into a location like the 'rapid' waves from the logs. It gives the effect of a turbulant lake or a rough ocean, with very choppy waters in the wave pool areas. These machines are usually perpendicular to the water flow and channel direction, meaning the waves come at you from a right angle to the direction the boat is travelling.
Thorpe Parks wavemaker is still operational, I believe. As are many others on many rapids around the world. They were one of the most popular additional features sold on older-generation Intamin Rapids rides.
Congo River Rapids is one of the few with three associated wavepool areas where the channel width widens quite substantially to slow the water flow in order to maximise the effect of the wavemakers.
It would be great if these were turned back on. I see no reason why they can't. Parks are just scared, I think. Not surprising.
Just to quickly address the claim the ride seemed faster. This is just your memory playing tricks on you. The speed of the water is determined by 4 factors and 4 factors only. Gravity, the gradient of the channel and the width of the channel and the volume of water travelling down the channel. Non of these have changed.
There is no speed option to turn the speed up and down. It is one speed and one speed only. Determined by physical limitations such as concrete and gravity. To change the speed in any meaningful way, major alterations would be needed to the rides channel.
As I've said a few times previously, the last updated legislation (which was essentially updated twice after the Draytons incident, may I add) relaxed the original, harsher rules placed upon these rides. The original post-Drayton legislation basically said that anything that can encourage guests to stand should be removed. The new one is now much more in line with how they were before the Drayton incident, even going so far as to acknowledge that features such as water cannons (one of the worst things for guests standing) will be on these attractions. The tone has changed from removing everything that could encourage guests to stand to understanding that guests will stand as a result of the rides features and managing those risks better when they happen. Far, far better, in my opinion.
I guess that before HSE had all the facts around the incident, they imposed harsh rules just in case the cause of Drayton's rapids was much more serious. After the conclusion of the investigation, it was clear what caused the incident, thus going forward, risks can be managed better, hence them pretty much reverting to how the rules were around rapids rides before the Drayton incident.
Anyway, the TLDR basically means Alton has nothing physically in place preventing them from operating the wavemakers.