As indicated by the inquiry,

Normal dislodging by an individual = 0.04 m3

Normal uprooting by 500 people = 500 × 0.04 = 20 m3

Subsequently, the volume of water brought up in lake = 20 m3

It is likewise given that,

Length of lake, l = 80 m

Expansiveness of lake, b = 50 m

Stature = h

Volume of water brought up in lake = 80(50)(h)

20 m3 = 4000h

h = 0.005 m = 0.5 cm

Subsequently, raise in the tallness of water = 0.5 cm.