How to create daily average from hourly data

Hi guys,

I'm looking at river levels in an area where I may buy property. The data given to me by the local council provides a reading of the river water level every 15 minutes (for several years). If possible I want to create daily averages and plot them in a graph so that I can see the average level for each day.

I've attached a sample of the data running over a few days (The entire data set covers a decade). I need a function for the "average volume" column so that I won't have to enter the data manually thousands of times.

Any help would be greatly appreciated

An Excel Novice