Wednesday, April 15, 2009

Creating a river habitat

Scientists working to make a spot where fish flourish

Julia M. Dendinger News-Bulletin Staff Writer; jdendinger@news-bulletin.com

Belen Although the temperatures have crept into the low 70s recently, at 40 miles per hour on an air boat zipping up the river, things are a bit nippy. Anders Lundahl, a hydrologist with the Office of the State Engineer, sits easily in the bow of the boat and points out now barren sand bars.

He can't say anything over the roar of the giant fan propelling the flat-bottomed boat until it comes to a halt.

"It looks pretty barren now," Lundahl said. "But you would be surprised how quickly native species like the willows come back."

For the last month, personnel with the Interstate Stream Commission (ISC) under the Office of the State Engineer, along with Wilco Marsh Buggies and SWCA Environmental Consultants, were out on the river working on habitat restoration for the silvery minnow, an endangered species.

From April 15 through mid-August, the river is "hands off" until migratory bird season ends.

This work is the first phase on the Isleta reach, or the part of the river from the Isleta diversion dam south to the San Acacia diversion dam.

The project is backed by a federal nexus of agencies that are part of the Middle Rio Grande Endangered Species Act Collaborative and funding for the nearly $800,000 project comes in part through the New Mexico Water Trust Board and the collaborative,

The large sand bar that the boat is anchored to had a decidedly trammeled look to it. The soil has been churned and chopped by the treads of the excavator, and spindly stumps are all that's left of small trees.

Lundahl again emphasizes that what is happening is a good thing - really. As the level of some sand bars is taken down by two to three feet of excavated dirt, the work is strategically creating suitable habitat for the endangered silvery minnow.

"What we have here is a double-edged sword," the hydrologist says. "For years, the Rio Grande was a braided river and very unstable. As people settled in the area, they stabilized the flow."

A braided river exhibits channels that split off and rejoin each other to create a "braided" appearance.

As more people began to make the areas along the river their home, they began to contain the flooding and prevent the water from wandering. "We have done a really good job at making this a water delivery system," Lundahl said. "It carries a lot of water very quickly for irrigation and to meet our water compact agreements with Texas."

But as the river became deeper and faster, something else was happening. Without regular over banking, or flooding in the common parlance, one small fish was struggling to survive.

The silvery minnow, often thought of in hostile terms by farmers along the river, became an endangered species and the state was forced to do something to ensure its survival.

At first, Lundahl said, biologist thought the fish preferred to spawn in the deeper waters. "They thought that they spawned and then the eggs drifted downstream," he said.

As the minnow has been studied, scientists are now finding that for spawning and recruitment the minnows prefer slower, shallower, warmer waters that are found in overbank and backwater areas along the river.

"In 2005, we had a lot of inundation of the flood plain and they saw an increase in the minnow population," Lundahl said. "They saw a correlation - the more water in the river, the more flood plains are created."

Now work is being concentrated on trying to help the river get back to a more "wild" state so that habitat that was created naturally decades ago can once again form for the minnows.

As the sand bars are lowered, the vegetation along the banks that is taken out is used to create weirs that run perpendicular to the river's flow to create backwater habitat. The removal of the vegetation takes out a lot of nonnative, high water usage species such as the Russian olive and salt cedars, thus giving native willows a fighting chance to reestablish themselves.

And by putting the vegetation and small trees into the river's waters, Lundahl says, biologists believe that may also increase the food supply for the fish.

"They have come to think that the lack of wood in the river may have lead to depletion in the food supply for the minnows," he said. "They know some diatoms and other organisms start on the wood and because the river has become so swift, the wood is swept downstream and not deposited along the way."

When it comes to habitat restoration there are two general camps on the subject, Lundahl said. There is the process-based approach and form-based method.

Form-based is literally creating forms you want to use to create good biological and hydrology interaction, Lundahl said.

"The process based is to remove a small portion of a sand bar and let the river do the rest," he said. "The river is now so stable that the 'process' doesn't happen. The fish are struggling because of the stabilization."

Moving tons of dirt and excess vegetation to extend the minnows' habitat isn't something that is done on a whim, Lundahl said. There is anywhere from six to 12 months spent studying the area to be worked and then designing the changes scientists want to see implemented.

"As soon as we touch the water, we are subject to the federal Clean Water Act," Lundahl said. "We are under the same compliance requirements as everybody else. We're the state, so we are held to the highest standards."

Because the silvery minnow is an endangered species, if there is enough "take" or loss of the little fish, the federal government can come in and regulate and manage the protection of the fish, Lundahl said.

"By doing projects like this, it is less likely that the federal government will come in," he said. "These are non-water solutions. By establishing a good riparian habitat for next spring and establishing a strong population, we won't need to release water into the river.

"This will be sustainable and won't require the release of leased water to keep the river wet. That will also reduce costs by not requiring the state to pay for those leases."

Lundahl said the project is trying to implement some of the Middle Rio Grande Conservancy District's (MRGCD) methods for keeping the river wet. At drainage ditches along the river, the MRGCD has put "snags" where their ditches meet the river. The flow in those spots causes scouring, digging depressions beneath the snags that hold water.

By maintaining these "perennial pools," there will be a source of water available for the river and the minnows during dry seasons.

In the area south of Belen where a bosque fire raged in 2007, while most of the decimated trees have been removed, several were simply pushed over and left with exposed root balls for the inundation of the river.

As the flow rates increase and the water comes over the banks, it will encounter seven acres of subtly tiered land. Preparing for flow rates of 1,500 cubic feet per second, 2,500 and 3,000, the newly bladed area looks like nothing to the naked eye.

But Lundahl knows where each level is and has high expectations for the project, even if no one knows the outcome yet. "We think we know what they fish need and want," he said. "We're pretty sure we are interpreting our observations correctly. But ... it's all a learning process."

Part of that learning process has included some pretty high tech tools, Lundahl said. By using a LiDAR or Light Detection and Ranging unit from an airplane, the state was able to obtain a digital model of the entire Isleta reach that was accurate to within 12 inches.

The LiDAR sends out light and then measures how long it takes to return to the source. "With the LiDAR, we have a much more accurate model and elevation than we would surveying on foot," Lundahl said. "We even know the elevation of the vegetation and can create models that predict flow, erosion and deposits. Those models let us plan for work on the entire reach. There is work to be done for a very long time."

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