Trend Analysis in flow/dry rivers in arid/semi-arid climates

[Malequinn]

Hi,

Please assist me with an approach or framework for applying time series trend analysis on a river discharge for a very weird river. The river has alternating phases or flowing and zero flows. i.e can flow for 40years, dry for 30years, flow again for 30 years, dry again for 20 (dry I mean literally zero flowws. This is all in annual temporal scales. 

Or trend analysis does not apply to such data?

Thanks