Walls – Fixing wall with constant moisture over the years

From the pictures it looks like the cracks may only be in the stucco, and the underlying structural wall may be unaffected. It's hard to tell without actually inspecting the wall, but my guess is that these cracks are only skin deep. However, you will want to treat them to prevent them from spreading.

Here is a good article about Cracks in stucco.

Here are some excerpts from the article.

All buildings are subjected to a variety of stresses in various forms and this stress is often transferred to the plaster stucco membrane.

Stucco is not and never was intended to be a structural material.

Cement stucco is a relatively thin, brittle shell over a framed structure and can crack if the stresses are transferred and overcome the strength of the plaster membrane.

SHRINKAGE STRESS

All Portland cement shrinks as it cures. Controlling and minimizing that shrinkage is critical to minimizing cracks

Shrinkage cracking tends to have a map-like cracking pattern.

OUTSIDE SOURCES

Structural loads, lateral force racking, thermal changes, wind, lumber shrinkage and seismic events are all examples of outside sources of stress.

HOW HARMFUL IS A HAIRLINE CRACK?

a hairline crack does not automatically mean the stucco is faulty, failing or will not function for the service life of the building.

MAKING REPAIRS

Once the decision is made to make repairs, there are several options.

Option 1: Treat the joint with the same finish material.

Option 2: Paint the wall or ceiling after treating the crack with an acrylic paint or paint designed for stucco.

Option 3: An elastomeric paint coating.

Option 4: Recoat the wall from architectural break to architectural break with the same finish material.

Option 5: A new basecoat and mesh over the wall area.

1 Cubic foot of water equals 62.48 pounds - the trick here is calculating the lateral pressure, but doing a little googling I found the following formula:

R =(62.4)(L)(H squared)/2 (R = pounds force)

The force water exerts is equal both sideways as vertically, so using this calculation we can determine the force that will be exerted against the wall at its lowest exposed point by using the long width of the pond as L and 13" (call it 1.1)

62.4*30*(1.1 ^ 2) all over 2 = approximately 1,133 pounds over 1 square foot of lateral force at ground level, which translates to a pretty measly 7.865 pounds per square inch (1,133/12/12). (If my math is right, and I think it is a TAD low because if you imagine a column of water 1 inch square and 30' high that's 360 inches of water which is 360 cubic inches which is about a gallon and a half, and a gallon is 8 pounds (pints) ("a pint's a pound the world around")

Since your cement block is filled with gravel and rebar and you've got 1k lb concrete between the two wall layers - I'm reasonably certain that your wall strength combined is sufficient. However, to be ABSOLUTELY certain, you should consult with a structural engineer who can do all the complex engineering calculations that go into figuring lateral, axial and compressive strength of concrete, etc...