Avoid over-use of 'and' and 'but'
Occasionally, it is fine to use 'and' and 'but' at the start of a sentence, but more formal linking words and phrases such as 'moreover' and 'however' are often more effective and more precise.
Less formal:
(1a) River flow increased from 4.5 m3/s to 25 m3/s between the dam and the basin outlet. But river discharge in the lower basin fluctuated only insignificantly.
More formal:
(1b) River flow increased from 4.5 m3/s to 25 m3/s between the dam and the basin outlet. However, river discharge in the lower basin fluctuated only insignificantly.