New riffle below the former Florida drop structure. Click this photo to link to the annotated album Ronnies River Reports. (The water intake structure for Overland Golf course is in the upper right.)
Ronnie Crawford. – Unofficial River Conscience of the Florida Ave/Overland Stretch. 5/20/2015
Ronnie’s River Reports will be winding down as work on the Overland stretch, Florida to Evans Avenues, of the Denver South Platt was scheduled to be completed by now. The ongoing rains have put them back a few weeks as the DSP has been roaring for a month. Today (5/20) at the ENGLEWOOD station, it is at 3,000 cfs and 4,000 cfs yesterday-Tuesday. The DSP has been over 2,000 cfs all month and is scouring itself, as it does annually. The normal Summer flow through Overland is 75-100 cfs. The scour is a good thing and every year when I walk into the river for the 1st few times, I see many changes in the configuration of the bottom.
Last fall the 8 foot high Florida drop was removed and replaced with a 2 1/2 foot drop. The new river, below the new drop, was lined with large rocks 1-2 feet in diameter and mashed down with the “little yellow machines” so they won’t be displaced with water flow. I’m not sure why they did this, as it impedes the scour below the drop.
On upstream toward Evans Ave, are several more small drops. I asked Brian Murphy, of CDM Smith ( the engineers) what the depth between the drops would be at 75-100 cfs and he stated “about 18 inches”. An 18 inch depth for a hundred yards between drops doesn’t seen like enough depth to support much fish and there are no plans to make it a riffle for the trout and bass to feed in. Its a sculptured section. I asked Brian why they didn’t dig it deeper and he said “because the bed-rock was closer to the surface than they thought.”
The bed-rock there is a hard Colorado clay, not rock. It is removable with the earth moving equipment that Naranjo has. In my eyes, they could have dug into the clay, to create some depth and habitat. (Naranjo Civil is following engineering plans and is not responsible for the depth.) On up toward the bend in the river, a jetty is being built that extends into the river about 20 feet. This should work out well and push the water to the west side for a good scour along that bank.
The DSP, between the Florida bridge and Sanderson Gulch will be changed forever, some good and some bad. All of the holes on the west side are filled in with large gravel. It was suggested that a large structure be placed in the WEST channel under the bridge to create turbulence and help push the gravel out of the holes. These are some of the best smallmouth and rainbow holes in the DSP. This is where I caught my 18 inch (measured) smallmouth last summer. A large boulder structure was placed under the EAST channel of the Florida bridge at our suggestion. This has cleared out a deep and extended hole on the east side. This area looks good.
I like what they have done out of the river on both sides. Crusher fine walking trails have been put into place to get pedestrians off of the hard surface trail. Viewing and seating areas have been built, trees and indigenous shrubs have been planted. Most of this work is on the EAST side and it is going to look really nice.
Brian Murphy, says that it may take a year or two for the river to sort itself out. I understand that. What I find objectionable is;
- 1) That they miscalculated where the bed-rock was and didn’t dig deeper into it, to create an acceptable habitat between drops,
- 2) Lined the bottom of the river below the new Florida drop, which will impede future scouring,
- 3) Let all of the classic holes south of the bridge, WEST channel fill in. The engineers don’t think this can be changed.
All along the hydrologists have told me how unpredictable water is and I understand that. My concern is that when the river finally sorts itself out, the “little yellow machines” will be long gone. It is my amateur opinion that things can still be made better while the big machinery is still in the river.
Overall, the out of river improvements are really nice. Michael Bouchard, Denver P+R Project Manager has done a good job. Salute..! The in-river changes appear to be net loss as far as fishing habitat is concerned, in my humble opinion. I want to be wrong on this…..time will tell.
Thanks, Ronnie Crawford. – Unofficial River Conscience of the Florida Ave/Overland Stretch. 5/20/2015
Editors Note: Brian Murphy, managing engineer on this project for CDM Smith, provided this additional information and response 0n 6/2/2015
“It is true the new channel is not deeper because of the bedrock – a “hard Colorado clay” bedrock is in fact difficult (and therefore expensive) to excavate – but the new channel depth was also based on the slope we had to work with from the upstream tie-in to the downstream tie-in below the new drop structure, and the channel cross section. The new channel follows the bedrock profile exactly from upstream to downstream. The river used to follow a similar slope before the drop structure was installed in the 1970s.
Even if we had not hit bedrock, digging the channel deeper between the main riffles would not have been sustainable because the new channel would have filled up with sediment similar to the old channel behind the 8’ drop structure. The sedimentation would occur due to the top elevation of the riffles and drop structure being above the bottom of the main channel. The elevation of the new drop structure was the controlling variable – it is critical to the water delivery system that provides irrigation water to Overland Golf Course.
The 18” minimum depth in the new channel may not be optimal for carp and trout. Unfortunately this plains river wants to be shallow and wide in this stretch. The constraints listed above limit our ability to create a narrow and deep channel here. With that said, the design did include floodplain benches to increase the overall channel depth. In addition, the design included a pool downstream of each riffle and the drop structure for aquatic habitat.
As for the filling in of the holes south and north of the Florida Avenue bridge west channel, the river is doing what it naturally does – moving water and sediment. Those holes were originally created by the old drop structure. The drop structure captured and removed most of the sediment so the water downstream of the drop was “starved” and “hungry” for sediment and scoured out the holes, which are in a bend where they naturally form. I still expect holes to form in the bend, but they will fill and scour with sediment throughout the course of the runoff cycle. I do agree that the depth of the holes will be less because of the increased sediment supply.
I realize and respect that the river is different than it was nine months ago. It is adjusting to yet again another new paradigm.Nevertheless, the river and its ecosystem are healthier now than before the project. The fish will come back, just give it time.”
Brian M. Murphy, P.E., P.H., CFM, D.WRE.