The problem with diverting water is that it goes somewhere else. The issue is that Salisbury is in the way of the ocean. Trying to build your way out of that is not going to work. They could establish an annual sand budget and treat it just like snow removal.
I'm not sure water needs to be diverted, per se. The problem isn't baseline water level but waves, and especially large waves, and sand washing away. It seems like the solutions would involve some combination of:
* Breakwaters, to equalize the water levels and reduce the waves
* A few meters inland, some kind of wall (firmer than sand) which doesn't wash away, so a bigger wave doesn't impact homes
* Perhaps some kind of reinforcement underneath the sand
It might reduce littoral drift a little bit, but as I understand, this would be done the length of a rather long coastline, so that's not really an issue.
I have very mixed feelings about just dumping tons of sand into the ocean each year. That's going to have its own impacts.
You seemingly don't understand the costs and long term effects of what you're asking.
Just dumping sand on the beach is positively cheap compared to the hundreds of millions you're asking for. Also, building a wall near the ocean is possibly the worst idea you could ever do. Please research the interaction between air, water, and sand to learn this is how you make a massive hole that swallows everything. The same is true with breakwaters. Constant refurbishment is needed, and it changes sand flows that affect other people.
This seems like the sort of problem we ought to learn to solve. That's why I'd like us to try things, and I'm happy to have a little bit of my tax dollars involved. This problem will only be more and more common.
If you want a book that directly faces the problem look at "Pitfalls of Shoreline Stabilization: Selected Case Studies".
Of course you'll want to balance that out with books that just talk about the general challenges and successes, in which I'd recommend just looking at books.google.com on writings by the US Army Corp of Engineers. They talk about practical mitigations for different types of erosion.
Most success stories are going to be based on things like using plants/growth to trap and build sand, which typically means lowering human access to the beach and ensuring tall things that interrupt wind flow are not near the beach. For example mangroves in climates that allow them to grow.
There are also plenty of examples poing out by the C of E on things that cannot be solved. If you built a city near a portion of the beach that was eroding long before humankind appeared in to the picture, all you can do is slow that erosion and at great expense. The ocean is far more powerful than you can imagine.
