The dimensions of storage coefficients is:

Concepts:

Storage coefficient:

• The water yielding capacity of the confined aquifer can be expressed in terms of its storage coefficient.
• Storage coefficient or storativity is the volume of water released from the storage per unit decline in Piezometric head, per unit area of the aquifer(not from the entire aquifer). 
• It is a dimensionless parameter. 

Coefficient of transmissibility (T):

• The rate of flow of water through the entire medium of unit width under a unit hydraulic gradient is termed the coefficient of transmissibility.

Specific Retention (Sr):

• Specific retention of a rock or soil is the ratio of the volume of water a rock can retain against gravity to the total volume of the rock.
• In coarse gravels, the size of the pores is large, due to the large size of pores, water holding capacity against gravity will be less. Hence the specific retention will also be less.

\(\left( {{S_R}} \right) = \frac{{{Volume\;of\;water\;retain\;against\;gravity\;(V_{RG})}}}{Volume\;of\;soil} \times 100\)