Based on my understanding on how senate works in the US over 200 years, its function should have been to check the national government. Parliamentary motions would be passed only when the 2 houses agree. The idea is to promote give and take in the deliberations of both houses. It also tends to ensure that counties from regions with smaller populations(tribes) can carry more weight against extremist ideas from otherwise more populous counties(tribes).
Its pretty messed that they came up with the notion that it should check governors, who already have MCAs for that role.
Given that its role is now confusing, I think either the senate or the assembly should be scrapped. Scrapping the national assembly would save Kenya a lot more money and headache than scrapping the senate.