Drainage is usually interesting. If I had drainage like that that was vegetated and working, I wouldn’t mess with it.

For background, I live in a canyon that is a little over seven hundred acres in a ranch that is a little over nine hundred. One inch of rain in the canyon results in 58 acre feet of water. When the soil is saturated that is a lot of run off. I’ve put in a couple thousand feet of four foot CMP, probably a thousand feet of two foot ADS, thousands of feet of swales and probably close to a thousand feet of open ditches. I have put in a few hundred feet of French drain. The secret is to make a gravel burrito with heavy filter fabric and bury it. Exposed filter fabric will rot. Gravel that is not surrounded by something to keep the fines out will fill up with fines and become much like dirt but more of a pain in the neck to mess with.

If I had a super compelling reason to mess with what you have, I’d consider using a laser, digging a trench that daylights at the bottom of the existing swale just before it leaves your property, installing a French drain using 12’ wide heavy filter fabric and large, washed rock (river rock or crush in the ballpark of two inch size), filling the fabric so that when you folded it over the top you’d have about a foot of overlap, then using landscape staples to hold it until you covered it. I’d fold the landscape fabric and close both ends like a burrito. On the outlet end, I’d butt a short piece of culvert pipe against it and cover letting the the other end of the pipe daylight. I’d still leave a very slight swale over the top of the burrito and set drainage grates (with downspout pipes if needed) connecting to the top of the burrito to get the surface water down to the burrito quickly. This works, I used it to dewater a spring that was raising hell with the backstop to my range. It is also a lot of work with some not inconsequential materials cost. I’d never do it for a backyard swale like that. Heck, I put a swale in the yard at the house, not that aggressive, but a swale. I think we get a lot less rainfall than you do.

Talk to the city/county before doing anything. There could be an easement in that area specifically to address drainage which would preclude you from messing with the area at all.

My neighbor back in NC wanted to flatten his front yard...there is a ditch to remove water, and it’s in the right of way.

He called the DOT and a guy came out and looked at it and what neighbor wanted. Told him how to do it. Ie placing concrete pipe to the end of his property and fill it in and to grass it so the dirt wouldn’t run off.

My neighbor on the other side did the work. Took a day and a day for the sod.

You probably need to get permission from someone.

Almost 100% positive there is no drainage easement.
We have a really wide yard and that is the biggest spot for the kids to play but has a big dip.
Pretty much everything already drains to all the rear neighbors yards.
It is hard to tell in the picture but the left side by the fence is actually slopes toward the right.

Guess I’ll check with the Clerks office whenever they open again.

Then do what smlsig suggested minus the beer.

I'll guess that was put there for a reason by whoever designed your neighborhood. Definitely should research whether that's a good idea.

Doing something 'because it's your property' that causes thousands of dollars damage to your neighbors by circumventing the drainage plan definitely won't make you popular and could cost you a few law suits.

If you're in a HOA you definitely need to check.

Do you reside in a flood plain? Does the swale exist on both sides of your property? Is there a creek or waterway nearby that would catch the drainage? Be cautious before changing the natural flow of water . Google: altering the natural flow of water for some further insight.

Don't do it.

It's there for a reason.

Once rented a property, couple acres. There was a depression just like yours that ran the length of the back fence, the full length. I hated it because it was next to the fence and if you wanted to approach the fence, the top of it was now at eye level.

The depression ran south, then turned west and ran to the road. Hated it, too.

About 100 feet away (about equidistant from each depression) was a large mound of dirt. Perfect.

Shovels, wheelbarrow, rake. Spend about two days working my ass off getting it all filled in. Raked it smooth - man, it was artistry.

A few weeks later, had a big overnight rain. Look out my front door and the entire property is under about 10" of water. WTF?

The water was on the porch a few inches deep, and about 3" from the floor lip into the living room. We're talking near disaster.

Took me a bit to figure out it was man made (my new swamp and mosquito breeding pond). The water wasn't going anywhere, either. Maybe for days. Life has to go on - and walking in several inches of water to check the mail, dealing with constant wet dog because he was outside half the time...you get the idea.

Had to get busy NOW. No choice.

Shovels and wheelbarrow.

Took about four days, maybe five, and now it was all wet and weighed a lot more. Felt like digging a WWI trench. About killed me. But the water was gone - and I now understood that depression ran many thousands of gallons of water annually out to the road and onward to the canal system here.

There are things in your life you do - that you never forget.

Oh, and that mound of dirt had probably been there since the property was apportioned, because someone a lot smarter than me knew to dig ONCE.