A rower training to race will usually engage in regular, intense sessions on the erg or on the water. A rower training for health may row with less intensity, moderately, every day.
Suppose the rower for health decides to race. Does the level of intensity have to increase all the time or can she continue at a moderate pace?
It depends on the rower's goals. If the goal is to participate in a race, to try it, to experience the event and meet others, it is not necessary to train as if you are trying to win. Even at major events like the Head of the Charles, there are competitors out there who have trained in that way. They may be slower, but they are participating.
If the goal is to see how well you can do, you will want to ratchet up the intensity of some workouts. Do not plan to row easily at all times before an event and then have the ability to row the course at full power.
On the other hand, the moderate training you have done year round can provide a solid aerobic base on which to build as you begin to train to compete. Build on it with interval work. See how your body responds to shorter bursts of harder rowing. Watch day to day and week to week as your strength and wind improve.