Compare the two houses in terms of roles:
Chapter Eight - The Legislature
Article 95. Role of the National Assembly(1) The National Assembly represents the people of the constituencies and special interests in the National Assembly.
(2) The National Assembly deliberates on and resolves issues of concern to the people.
(3) The National Assembly enacts legislation in accordance with Part 4 of this Chapter.
(4) The National Assembly --
(a) determines the allocation of national revenue between the levels of government, as provided in Part 4 of Chapter Twelve;
(b) appropriates funds for expenditure by the national government and other national State organs; and
(c) exercises oversight over national revenue and its expediture.
(5) The National Assembly--
(a) reviews the conduct in office of the President, the Deputy President and other State officers and initiates the process of removing them from office; and (b) exercises oversight of State organs.
(6) The National Assembly approves declarations of war and extensions of states of emergency.
Article 96. Role of the Senate(1) The Senate represents the counties, and serves to protect the interests of the counties and their governments.
(2) The Senate participates in the law-making function of Parliament by considering, debating and approving Bills concerning counties, as provided in Articles 109 to 113.
(3) The Senate determines the allocation of national revenue among counties, as provided in Article 217, and exercises oversight over national revenue allocated to the county governments.
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4) The Senate participates in the oversight of State officers by considering and determining any resolution to remove the President or Deputy President from office in accordance with Article 145.Apart from removal of the President I do not see anywhere else where the Senate plays an oversight role over the National Assembly!