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Tue, Nov. 12

Agua Fria River crossing in danger of flood damage

A routine maintenance job at the Prescott Street crossing of the Agua Fria River in Dewey-Humboldt has caused a big headache for the town in its attempts to remedy the situation before the monsoon season hits in July.

The town contracts with four different companies to do routine maintenance work that includes cleaning the debris out of the culverts under Prescott Street, a low water crossing at the Agua Fria River. The crossing remains dry for most of the year, but heavy rains can result in flooding and closure of the road.

Grady's Excavating cleared the dirt, sand and debris out the culverts during the first week of March, and inadvertently deposited some of the dirt and sand in the form of berms upstream that narrow the channel.

Council members are concerned that heavy rain would cause an increase in velocity and depth of water flowing into and over the crossing with potential damage to the road and culverts, and possibly to residents' property along the river.

Recently the town council asked the town engineer to investigate clearing the dirt berms and vegetation upstream from Prescott Street in order to reduce flooding in the lower portion of the town. This would widen the channel, broadening and slowing the flow of the river, Mayor Earl Goodwin said.

He doesn't know with whom the town contracted to do the clean-up work or why the company piled the dirt in the riverbed.

"The problem turned out to be where the dirt was placed when they cleaned it out last time. We just want to get that dirt placement removed," Goodwin said.

He said he thinks the work was done while the town was in between hiring a new Public Works Inspector who would normally provide more direction to the workers.

Town Manager William Emerson reported back to the council at Tuesday's council meeting that Paul Gilmore with W.C. Scoutten, Inc., town engineers, determined that any modifications to the river bottom would necessitate obtaining a development permit from the Yavapai County Flood Control District.

In order to acquire the permit, a civil engineer must report on location and depths of excavations, location of trees and banks and their protection or disposal, hydrology and sediment aspects to the planned modification, erosion and channel degradation, water surface profile studies and quantitative sediment analyses.

The town would also need the agreement of three property owners along the river at Prescott Street.

"The town engineer concluded that such work probably would require extensive permitting and coordination, making a quick solution difficult," Emerson said.

One way around the lengthy permitting process is to qualify the modification work as an emergency.

Gilmore did not state in his report whether he thought the situation qualified as an emergency. Ultimately, it is the County Flood Control that makes that determination, Mayor Earl Goodwin said.

The mayor said he wants the town engineer to make a determination by April 15 whether the dirt berms constitute an emergency. The town could then ask the County Flood Control to rule on an emergency status, and if so, the town could hire someone to remove the excess dirt and gravel upstream as a temporary fix before the start of the monsoon season.

In the meantime, Richard Eis, Dewey resident and engineer with the Prescott National Forest, told Emerson he could start within two or three weeks and take care of the problem at a cost of $12,400 per week for up to four weeks of work, totaling $49,600.

Eis said in an e-mail to Emerson that Yavapai County Flood Control could issue a development permit for "routine maintenance." He proposed consulting with Ken Spedding, the Yavapai County Flood Plain administrator, on what would constitute "routine maintenance."

Eis recommends removing about 6,000 square yards of vegetation and about 10,000 cubic yards of material over a distance of 1,000 feet upstream and about 100 feet across the riverbed, depending on the determination of "routine maintenance."

Garry Rogers, whose property is about 400 feet upstream, said this makes no sense.

"Clearing the vegetation could increase rather than decrease flood danger and resultant damage," Rogers said in a three- page letter to the council.

The principal effect of vegetation, he said, is to slow flood water.

"Slower water carries less material and is less erosive, and more of it is absorbed as it flows across the floodplain," said Rogers, a former professor of physical geography.

Not all council members had a copy of Rogers' letter in front of them, but others in the audience reiterated what he said.

"When you remove vegetation, the water washes more soil down that will plug everything up," said resident Jack Hamilton.

Carol Williams, whose family owns seven acres adjacent to the river, said it was the 4.5-foot bridge and culvert that cause the flooding.

"That's the problem. Before that, the riverbed was kept clean. We used to drive through that creek bed all the time," Williams said.

One resident, Mark Sinclair, who also lives adjacent to the Agua Fria, blamed the abundance of willows growing in the river bottom for causing a narrowing of the channel and allowing the water to back up. Three years ago, Sinclair said he lost $3,500 in personal property, including a horse, during floods.

"It got within 17 inches of flooding my house," he said, adding that he also is concerned about people crossing the river before the Yavapai County Sheriff's deputies set up the barriers.

Rogers suggested that the town council have a hydrologist look at not only the crossing but also at the changes made in the landscape upstream that have affected the flow of water.

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