CIVE 633 - ENVIRONMENTAL HYDROLOGY
SALINITY MANAGEMENT (REISNER)

INTRODUCTION

A few hundred million years ago, the waters of the ocean were still fresh enough to drink.
The salts are all in runoff, leached out of soil and rock.
The runoff concentrates in rivers, which end up in the ocean.
On March 24, 1992, the concentration of salt along the coast off San Francisco was about 35,000 ppm.
What is changing is the concentration of salt in some of the world's rivers.

HISTORY

In the seventh century B.C., the Assyrians built the first inverted siphon, a feat of hydraulic engineering at that time.
The Hohokam, in Arizona, left 700 miles of irrigation canals.
Something arounnd 1300, the Hohokam vanished, reason unknown.
Egypt survived uninterruptedly for thousands of years.
All of the great civilizations were irrigated ones.
Cities grew with irrigation; work became more specialized.
The desert was a healthy place to live; no malarial swamp, no raging cold.
Canals could silt up or wash out with floods.
There was another enemy; something subtle, unseen, subversive.
This was salt!

IRRIGATION

Irrigation is a profoundly unnatural act.
There are hundreds of dead saline lakes.
In the U.S. West, many soils are classified as saline or alkaline (due to endorheic paleodrainage).
The process continues: salts are picked up, fresh water evaporates, more salts are picked up, more fresh water evaporates.
Out of 120 million ac-ft of irrigated water, 90 million evaporated (evapotranspiration); the remaining 30 million contained virtually all the salt (Na Cl).
At the Pecos river, the salinity is 720 ppm; thirty miles beyond, the salinity is 2020 ppm, almost entirely due to irrigation.
The Arkansas river contains a trace of salts near its headwaters; 120 miles downstream, it contains 2200 ppm.
The Colorado river has the worst salt problem (because it drains a paleoendorrheic basin).

DRAINAGE

Drainage becomes the most difficult aspect of irrigation.
Salts built up in the root zones.
You can drain the fields, or build desalination plants, but you are left with the saline wastewater or pure salt to dispose.
Salinity is the monkey on irrigation's back.
The amount of lands going out of production due to salinity now surpasses the amount of lands being brought into production with new irrigation.
The Sumerians (present-day Irak) struggled with salinity.
They had to switch from wheat to barley because wheat is less salt-tolerant.
Sodium ions tend to be absorbed by colloidal clay particles, deflocculating them.
This leaves the resultant structureless soil almost impermeable to water.
In general, high salt concentrations obstruct germination and impede the absorption of water and nutrients by plants.
Groundwater becomes extremely saline.
Iraq feeds itself mainly through oil exports.
The solution is better management, careful management.
Certain crops can take high salinity levels.
Cotton can take 5900 ppm.
This shows that you can use water on one crop, then on one that tolerates salt better, and so on.
The cost of Yuma's desalination plant is $300 million.

THE WELLTON-MOHAWK SCHEME

The Wellton-Mohawk region in Arizona is plagued by poor drainage (and a lot of salt, drained by the Colorado and deposited near its estuary)
In the 1960s, the USBR installed an elaborate drainage system to carry the waste-water away.
The salinity of the Colorado river in Mexico shot from 800 to 1500 ppm.
We promised Mexico 1,500,000 ac-ft of water a year, which they are getting.
The compact contained no guarantees about water quality, only water quantity.
In 1974, a new agreement was reached to deliver to Mexico water with no more than 115 ppm higher than measured at Imperial Dam (879 ppm).
Salinity levels of 1000 ppmn or more are a violation of international law.
The simplest way was to buy out the Wellton-Mohawk farmers and retore the land (keep the salt in the profile).
Retiring the Grand Valley of Colorado, another prodigious source of salts, would be further insurance against the problem.
The UBSR solution was a reverse-osmosis desalination plant.
Energy costs could easily push the Yuma plant to 1 billion over 50 years.
UBSR is purifying water at $300 an ac-ft so that upstream irrigators can continue to grow crops with water that costs them $ 3.5 an ac-ft.
Better irrigation management could mitigate the problem.
Laser-leveling field and escalating crops to match salt tolerance.
Salinity levels at Imperial Dam could reach 1150 ppm by the year 2000.
This is bad news for the Mexicans and for Los Angeles. We use the water too.

THE SAN JOAQUIN VALLEY

In the San Joaquin valley, the perched water does not have a chance to mingle with the relatively pure water downstream.
The more the farmers irrigate, the higher it rises.
The water planners wanted to build a master drain to carry the perched water out of the valley.
The State Water Project would make no sense without a drain, because it would add water to the perched water.
No drain exists to date.
The San Luis Drain was built, but it has nowhere to go until the master drain is built.
Solving the drainage problem would cost 4-5 billion!
The USBR created an artificial marsh at Kesterton to write off debt as wildlife benefit.
In 1982, biologists began to observe damaging effects on overwintering birds at Kesterton.
The culprit was selenium, a rare mineral, toxic in small doses, that occurs in high concentrations in southern Coast Range soils.
These soils formed the Westland Water District, which drained its irrigation return flows into Kesterton.
The solution is to drain, but the people of the Bay Area applied the NIMBY rule.
The San Joaquin valley farmers asked for water and they got it, asked for subsidies and got them, and now they want to use the Bay as a toilet.

ASWAN DAM, EGYPT

In Egypt, through time, the floods carried away the salt, and deposited a fresh layer of silt.
In the 1960s, the Egyptian government built a high Dam at Aswan, with Soviet help.
Now the springs floods are gone, the nutrient-rich soils no longer come, the Nile sardine fishery is gone, the reservoir is silting up rapidly, irrigation canals are being scoured by the silt-free water released by the dam, and the salts have arrived.
The Egyptians have been irrigating madly, and the water table has been rising, increasingly poisoned by salts.
Egypt was in an estuary, and flood flushing helped move the salts out.
Now, without floods, and with more salt, they are doomed.
Pillsbury wrote:
There is not enough waste water flow left. The lower rivers should be allowed their natural function which is to export the salt to the ocean. Otherwise, today's productive land will become salt-encrusted and barren.

My commentary:

A river's natural function is to carry salt and sediment to the ocean.
For this, they need "enough water" to serve as the carrying medium.
Anthropogenic consumptive use of water (irrigation evapotranspiration) takes away a portion of this water.
If the river cannot carry the salt, the salt will remain behind, degrading the land and its landscape.
Domestic water supplies are small compared to irrigation (usually about 1 to 10 ratio).
One solution is not to irrigate, but this is obviously not feasible.
Another solution is to pay for desalination, at whatever cost, and learn to use the byproduct.
Pure NaCl salt can be sold, so it is not a total economic loss.

Saline flats at Guerrero Negro, Baja California Sur.

NaCl is used as means to safely transport its elements, Cl and Na, over long distances.
Fresh water salinity polluters need to pay for their actions.
These are usually farmers, and traditionally they have refused to pay.
A U.S. example: The Imperial Irrigation District (IID) and the Salton Sea.
IID refuses to bear responsibility for cleaning tha Salton Sea.
Imperial valley produces winter crops, so all society benefits.
Now 200,000 ac-ft of water from the Imperial Valley will be transferred to San Diego.
Can the Salton Sea be cleaned, or restored?

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