Aguaje de la Tuna


The sediment retention dam at Aguaje de la Tuna has resulted in the degradation of the streambed, to a depth of approximately 8 m, reaching the underlying bedrock.

[VMP] Good morning.

We are here

in the Aguaje de la Tuna,

one of the watersheds that drains

into the Tijuana river,

in Tijuana, Baja California, Mexico.

We are accompanied by

Alberto Castro Garcia,

a hydrologic civil engineer,

practicing in Tijuana.

[ACG] Good morning to all.

I wish to thank Dr. Ponce

and his team of

San Diego State University students

for the opportunity

to present to you a few aspects of

Tijuana's hydrology,

particularly about this creek,

which is referred to as

the Aguaje de la Tuna.

In 1991, there was a heavy storm

in the city,

which produced a flood in this basin,

transporting a large quantity of sediment

to the mouth of the basin.

In 1993, an extraordinary storm event

pounded the city, especially

the Aguaje de la Tuna.

About 400,000 cubic meters

of sediment

were dumped into the delta.

As a consequence

of this situation,

the need was felt to construct

flood protection works,

consisting of channelizations

and sediment retention dams,

like the one shown here.

It is practically at the level

of where I am now standing.

This is the base level

of the first retention dam.

The objective of this dam

was basically to retain sediment.

Originally, the dam was designed

to retain a certain amount of solids.

During the useful life

of the structure,

degradation occurred,

which led to the construction

of a first step.

Ten years later,

another step was built

because degradation continued.

The steady erosion by water continued,

and the erosion depth eventually

reached the underlying rocks,

classified as shales,

as observed here.

[VMP] Here we are located at a distance

of approximately 50 m downstream

of the sediment retention dam.

As you can see,

here the amount of degradation

of the creek bottom

has reached the underlying rock,

which appears to be a disturbed shale.

Here we have an example of

a modern-day geologic, anthropogenic process

in which a small canyon

is being formed

in the rocky streambed

of the Aguaje de la Tuna watreshed.

[VMP] Here we can observe

a curiosity of Nature ---

how the water flowing

in this reach of the

Aguaje de la Tuna,

above the rocky shale bottom,

has been able,

over the past 20 years,

to carve out this feature,

basically a natural dam

of irregular shape,

apparently a spillway,

but with intermediate channels.