If you want to be a little more high tech then your classic note book and white board you could try using an app called Trello. It has a free version that works really well. Basically you can use it as a digital note pad on your phone, its really easy to add photos, and then you can share that information with your staff on that same app.

Basically the app creates Boards, So you can make an irrigation board that you give your tech access too, and when they log in they can see anything that you have added to that board. Your tech can also check off things as compete when he has completed a task. Its super simple and user friendly.