What can we do to fix these problems.😢

you will have to install landscape fabric and top with mulch or stones

First, I would make a report to BBB about the contractor. I use Round-up or similar weed killer on unwanted vegetation that has already sprouted. You should cover the plants you want to keep (a bucket works when they are spaced out like yours) and don't spray when the wind is blowing or it may creep over to plants not protected with buckets. Here some info to get you started on finishing the dry river bed: https://www.diynetwork.com/how-to/outdoors/landscaping/how-to-install-a-dry-creek-bed. Can you adjust the flow in the drippers that are over-watering or change to a smaller size nozzle? Hope this helps.

First, call the guy back out that installed the decomposed granite and show him where the grass is growing through and see what he has to say and what he will do to fix - on HIS dime! He needs to fix with no money from you. He did not perform the task correctly, it is his responsibility to make good and keep you happy!

Call out a professional landscaper to clear up any irrigation issues you may have.

What is the issue with the dry river bed? What needs to be added?

Warm enough for you today? 89 here in Castaic. Too soon to be this hot! 🌞

The dry river looks okay, but have that irrigation person comeback and balance the system. I’ve done drip irrigation for my veg garden for a few years now. I’m not sure what system they put in...but I have restriction devices that limit the amount the amount of water to be delivered To each plant, I don’t bury mine...to many trees and thier roots. Do you know where he got the supplies? I’m not seeing any drip emitters or water spikes.

Here's a good article on killing St. Augustine.... http://www.thesurvivalgardener.com/get-rid-st-augustine-grass-four-simple-ways/

I can see where the bank has collapsed. The watered areas look pretty good to me. If you don’t live in the desert, I don’t think you can completely eliminate most weeds. You could poison the weeds regularly, but if you do it enough, you might affect the rest of the green growth. Whether you dig up the yard and put down heavy plastic or not, I suggest putting a thick layer of mulch wherever you don’t want weeds and grass. And I would add small pebbles, a ton of them, to the riverbed and up the banks. To avoid digging out the channel again, I would just place some wide pvc or rubber pipe down through the center until you have the smaller rocks in place, then pick up the pipe, leaving the channel. Best wishes. ☺️

Grass growing thru granite ? The most fun way to kill off the grass is to burn it with a propane torch. You can buy a set up that is used for roofing. Just burn them. Fine for the enviornment.

My experience has been that even if you put down a barrier prior to DG, gravel, rock, etc., you will ALWAYS have some type of weed growing that you don't want because the seeds will blow in on the wind or bird dropping will bring them in. The best thing to do is find a spray that works, eradicate it best you can and then just stay on top of it until it is minimal.

Can't see really clearly if the yard has a slope to the one corner.... you might have to install "pressure compensating" drippers.... choose the gallons per hour that you want and install them in the 1/4 inch drip line.... the drippers keep help keep even pressure on the whole line so one part does not get more water than another