1. Hydraulic Cover Stones (HCS)
By Dave Derrick,
Potomologist & VP,
River Research & Design, Inc.

2. THIS METHOD IS A DAVE DERRICK DISCOVERY (DDD)

3. Hydraulic Cover Stones (HCS)
Hydraulic Cover Stones (HCS) are typically large single stones placed in a flowing channel with the crest of the stone within inches of the base flow water surface elevation.
The constant movement & rippling of the water from the Hydraulic Cover Stones results in a type of cover, “hydraulic cover”, masking fish location from the view of predators. The stones also provide resting areas & within-channel refugia for fish during high energy, high-flow events.
Hydraulic Cover Stones are especially useful in sections of the stream with little in-channel structure, or vegetative cover, or undercut banks.

4. Hydraulic Cover Stones (HCS)
Large single stones placed in a flowing channel. Three versions:
1.) Top of the stone set at an elevation slightly lower than the typical base-flow water surface elevation. When sited correctly, the accelerated flow over the top of the stone will change from subcritical to supercritical flow, & immediately downstream back to subcritical (usually with a weak hydraulic jump). The hydraulic jump will entrain air & help aerate the stream.
2.) Stone crest set just below the base flow water surface elevation results in an acceleration of the water moving over the top of the stone, with “standing waves” (stationary waves) forming downstream of the stone.
3.) Stone crest set slightly above the base flow water surface, resulting in a V-shaped wake and flow split with a double return eddy flow pattern DS of the stone. However, these emergent stones might be used as perches for predators.

5. Hydraulic Cover Stones provide improved aquatic habitat
Hydraulic Cover Stones shown functioning 3 different ways. Graphics courtesy of Ecology & Environment, Inc.

6. UNKNOWN AGE – CEDAR RIVER, SEATTLE, WA-DERRICK 8-22-2012
UNKNOWN AGE – Looking a boulder acting as a HCS. Split flow, acceleration, air entrainment, & dead water DS of boulder.
“Based on the interagency publication, Stream Corridor Restoration: Principles, Processes, and Practices, this introductory training covers:
Stream corridor ecosystems and their components
Ecological processes, structure & functions
Characterization and analysis of stream corridors
Development of a restoration plan
Design, implementation, monitoring, and
Integrated, iterative, adaptive, flexible approaches”.
UNKNOWN AGE – CEDAR RIVER, SEATTLE, WA-DERRICK

7. Functions of Hydraulic Cover Stones
Provides micro-topography (scour & deposition)
Provides diversity of velocities
Provides “hydraulic cover” turbulence, surface water disturbance (boat wake), return currents, eddy fences, internal distortion, pressure zones, undulating surface water, standing waves, etc.
Provides feeding lanes for fish
Provides shape cover & solid substrate for benthics
Provides refugia during high flow events
Dissipates energy
Can aerate water, or de-gas super-saturated water

8. Boulder Clusters typically consist of a number of very large stones closely arranged in some type of pattern. The Boulder Cluster usually blocks a fair amount of the stream, with stone crest heights 2 to 3 ft above the base flow water surface elevation. Hydraulic Cover Stones are single large stones with the crest heights within inches of the base flow water surface elevation. HCS block a very small percentage of the cross-section of the stream.

9. (Purloined from Andrew Burg) This was not the designer’s intent.
Some concerns with Boulder Clusters (cluster too wide & tall here in a high bed-load stream)
(Purloined from Andrew Burg)
Shadow depositional sand bar splits flow, resulting in both banks eroding in a straight stretch. Little Sugar Creek one year after placement (1998).
This was not the designer’s intent.

10. Possible Problems with Boulder Cluster designs:
1. Excessive scour buries boulder
2. Cluster blocks large percentage of stream flow
3. Cluster redirects stream energy in unwanted direction (s)
Excessive deposition DS of cluster
Cluster too high, provides perches for predators/fishermen (

11. Hydraulic Cover Stone at Elton Creek, NY
Natural Hydraulic Cover Stones (HCS) on the Genesee River, Letchworth Park, NY photo taken 2003.
Flow
Hydraulic Cover Stone at Elton Creek, NY
Flow

12. Hydraulic Cover Stones on Eighteenmile Creek Project, Newfane, NY (constructed Sept. 2003)

13. My sneaker
Close-up of large stones to be used as HCS, these were hand selected, minimum 3 ft by 3 ft.

14. A Hydraulic Cover Stone (HCS) dug into the stream bed substrate for stability. The downstream wake is the “Hydraulic Cover”.
Flow
HCS

15. In a sand-silt bed stream, deeper excavation, or reinforcement of the substrate, might have to be accomplished so that bed scour does not cause the HCS to sink into the substrate.
Flow
HCS

16. Here comes Jimmy with a Hydraulic Cover Stone (HCS)
Here comes Jimmy with a Hydraulic Cover Stone (HCS)!! Water depths were measured & the correct thickness of stone selected for this specific location

17. Water depth was measured, & a specific sized rock delivered

18. Carefully placing the Hydraulic Cover Stone

19. Bed was dug & stone placed in hole
Bed was dug & stone placed in hole. Sediment near stone acting as a dye trace.
Flow

20. First HCS placed in Eighteenmile Cr
First HCS placed in Eighteenmile Cr., turbulence, energy dissipation, eddy fences…
Flow

21. Looking DS, note locations of Hydraulic Cover Stones during unusually low flow conditions

22. Crazy turbulence surrounds a HCS

23. Trio of Hydraulic Cover Stones working beautifully, note those wakes (the hydraulic cover)
Locals say this is the best fishing area in the creek (US of Cover Stones)
This is a cobble-bed stream. This technique might not work as well in a sand-bed stream (stones could subside)

24. HCS using up stream energy & entraining air into flowing water

25. Flow from left to right, note the hydraulic jump @ the Hydraulic Cover Stone

26. Looking US at a Hydraulic Cover Stone
Same Hydraulic Cover Stone, close up
Looking US at a Hydraulic Cover Stone

27. Multi-Use Hydraulic Cover Stones, in this case a fisherman’s resting rock, (FRR)

28. Salmon fishermen concentrating efforts among the Hydraulic Cover Stones, Eighteenmile Creek, Newfane, NY, Oct 2003

29. Fish those Hydraulic Cover Stones !!!!!!!!

30. NO NEED FOR A NET (if you’re good)
(FISH ON !!!)

31. On Saturday 10-19-03 (during the salmon run) folks are everywhere, 353 recreators by 9:30am.

32. Hydraulic Cover Stones on Cattaraugus Creek @ Savage Road, Sardinia, New York

33. Provides microtopography Provides diversity of velocities
Hydraulic Cover Stones for stable pre-dug “Pocket” scour holes in shallow areas (riffles & shallow runs)
Increases depths
Provides microtopography
Provides diversity of velocities
Provides hydraulic cover
Provides shape cover
Provides in-channel refugia
Dissipates stream energy

34. Catt Creek, looking US at riffle-run, measuring how high the Hydraulic Cover Stone will jut into current.

35. Hydraulic Cover Stone in pre-dug scour hole, stones measured to fit

36. Looking US at a series of Hydraulic Cover Stones, took 50 minutes to install 9 stones

37. Looking DS at same Hydraulic Cover Stones located in “run” section of stream. Previous condition was shallow sheet-type flow

38. Mini-Case Study: 1 of 3
Stone is here
A close look at a hard working Hydraulic Cover Stone during a high water event, Cattaraugus Cr. at Savage Rd. 11/4/2004

39. Mini-Case Study: 2 of 3
But relatively calm right at the Hydraulic Cover Stone, energy dissipated!!
Downstream of HCS fierce currents (water piling up on hip boots & bent pole)

40. Mini-Case Study: 3 of 3
Same Hydraulic Cover Stone during base flow conditions, not very impressive considering observed function during high flow

41. Hydraulic Cover Stone Quick & Dirty Flume Tests @ UB
On a series of short test runs were performed on a small 4 inch wide sand-bed hydraulic the State University of New York at Buffalo (UB). Flow duration ranged from 20 minutes to 45 minutes or so. Flow stage was supposed to mimic the Q-2 flow, but varied when we forgot to turn on the inflow hose & add water as the flume leaked. Our feet got wet. Discharge was varied a bit & not written down. Otherwise very scientific!!

42. Looking US @ the flume & flume-meister, Dr. Sean Bennett
SEAN BENNETT’S UB – ENTIRE FLUME - PIX DAVE DERRICK

43. THE EFFECTS OF STONE SIZE & ROUGHNESS ON NEAR-FIELD SCOUR AROUND A SINGLE HYDRAULIC COVER STONE

44. SEAN BENNETT’S FLUME @ UB – HYDRAULIC COVER STONES-DERRICK 11-11-10
3 Hydraulic Cover Stones. The upstream stone is small & aerodynamic resulting in very little scour. More scour as each downstream HCS is progressively larger & blocks more flow
SEAN BENNETT’S UB – HYDRAULIC COVER STONES-DERRICK

45. SEAN BENNETT’S FLUME @ UB – HYDRAULIC COVER STONES-DERRICK 11-11-10
a single HCS. The US face of the stone is square & vertical. Scour was so great US of the stone that it fell US into its scour hole!!! LESSON: SIZE & SHAPE MATTER GREATLY!
SEAN BENNETT’S UB – HYDRAULIC COVER STONES-DERRICK

46. This PowerPoint presentation was developed & built by Dave Derrick
This PowerPoint presentation was developed & built by Dave Derrick. Any questions or comments, call my personal , or Enjoy the information!!
“Based on the interagency publication, Stream Corridor Restoration: Principles, Processes, and Practices, this introductory training covers:
Stream corridor ecosystems and their components
Ecological processes, structure & functions
Characterization and analysis of stream corridors
Development of a restoration plan
Design, implementation, monitoring, and
Integrated, iterative, adaptive, flexible approaches”.

47. Speaking of size, presented here is Jackson Danger Rainer wearing Uncle Brent’s huge size 14 sneakers