This is the first of two additional questions that have Biblical references.
Q: Why did Jehovah Part the Sea for the Israelites to cross it but stopped the Egyptian Army by drowning them?
A: The Sea was never parted to help the Israelites escape the Egyptians by Jehovah, it was a rare physical occurrence that helped the Israelites escape.
A storm had created a long sand bank, which was only visible when there was a low tide. This sand bank was high enough to allow the Israelites to wade across a section of sea from one shore to another. The Egyptians were following them but were late in crossing and did not make it to the other side before the tide came in. The water flowing over the sand bank created strong undercurrents which swept the Egyptians off the sand bank. Most were not able to swim and therefore drowned.
From the position of the uneducated observer it would have appeared that God had saved the Israelites and drowned the Egyptians.