Assuming that a river bed level does not change and the

Assuming that a river bed level does not change and the depth of water in river was 10 m, 15 m and 8 m during months of February, July and December respectively of a particular year. The average bulk density of the soil is 20 kN/m³. The density of water is 110 kN/m³. The effective stress at a depth of 10m below the river bed during these months would be

1. 300 kN/m² in February, 350 kN/m² July and 320 kN/m² in December.
2. 100 kN/m² in February, 100 kN/m² July and 100 kN/m² in December.
3. 200 kN/m² in February, 250 kN/m² July and 180 kN/m² in December.
4. 300 kN/m² in February, 350 kN/m² July and 280 kN/m² in December.

Effective stress below riverbed does not depend upon the depth of water above bed level