Small harvesting structure over a bench

Our Community Allotment: https://permies.com/t/262302/Plot-community-forest-garden finally got our accessible bench installed, eight months after we started planning.

We're increasingly getting Spring & Summer drought, and torrential rain in Autumn & Winter.

We have no space for a shed, but there is a little storage space under the bench. So we urgently need to plan a rainwater harvesting system, and a well-designed & safe rain shelter for the new bench.

My initial thoughts are beyond my skill level: four strong posts, at least 2m high after being sunk in the ground, with a gently angled canopy stretching at least 15 cm beyond the footprint of the bench on all sides. Then a gutter along the back, feeding a securely lidded waterbutt.

But it then occurred to me that a simpler interim would be a tarpaulin for the bench. Coincidentally, the bench is right in front of our rhubarb patch which prefers to be well watered.  The simplest thing would be a roughly secured tarpaulin, and carefully lift the front to direct the gathered water over the back of the bench, if it's rained.

Then a development of the tarpaulin system would be a pair of poles, one sunk either side of the front low side of the bench where you sit.  With the back of the bench as the other support, this would create a simple angled cover to direct rain off the bench backwards towards the rhubarb patch.

We have hazel in need of coppicing to provide the two poles.

There's a good chance someone in our community has an old tarpaulin-style sheet they no longer need and would be happy to donate 'to a good cause'.

We finally have an 80% chance of (stormy) rain forecast next week, the remnant of former Hurricane Erin.  So we have a chance to immediately test the simple system next week.  I just need to source a suitable "tarpaulin-like" cover for the bench.

A tarpaulin with minimal support seems both less of a potential safety issue, as well as much less technically challenging to install!

Any constructive (!) thoughts welcome.

Image: AC sitting on the accessible, durable community bench

Ac, where are you located?

I think using a tarp would be a good quick solution - if you can get hold of one.
There are a few ideas on this thread that may be helpful: https://permies.com/t/161325/Creating-large-shaded-area-affordably. It's about creating shade, but using sheets of canvas, so similar enough I think.

I like the idea of using your hazel poles to support it. I managed to bend mine into a dome roof for my pallet shed, so you may be able to make an arch - although that would shed water all round rather than just backwards of course. The difficult thing will probably be tying the tarp on. Tarps usually don't have many hole round the edge, so you may find it a bit gappy at the front and need to make extra holes.

Many thanks for the pointers .. the uneven support for a longer-lasting tarp is really useful information.