CHAPTER 13 SECTION 7

Transcription

1 SEPTEMBER 30, 2008 CH13-700

2 TABLE OF CONTENTS 7.1 INTRODUCTION STRUCTURE SAFETY BOATABLE CHANNELS STRUCTURE INTEGRITY AND PREDICTABILITY CRITERIA FROM SECTION 6 DROP HAZARD REDUCTION FOR DROP Introduction Basic Hydraulic Design Considerations WARNING SIGNS Warning Symbols & Sign Examples PORTAGES & ACCESS OTHER CONSIDERATIONS RETROFITTING EXISTING IN-CHANNEL DIVERSIONS (RICDS) Introduction and CWCB s Role Adverse Floodplain Impacts and Durability Physical Characteristics of an Appropriate Stream Reach Summary of the Performance Index Flow Rate Guidelines for an RICD Hydraulic Engineering Definition of Control Design, Documentation and Record Drawings Liability GLOSSARY OF RELATED TERMS 718 SEPTEMBER 30, 2008 CH13-701

3 ANAYLSIS AND 7.1 INTRODUCTION Alteration to channels, rivers, streams, creeks, and other waterways (Channels) where public users are present require consideration of known and potential public safety hazards. Planning, design and construction of structures such as low-head dams, drops, chutes, bridges and armoring mandate a standard of care consistent with common sense safety concerns for the public that responsibly uses the rivers and waterways. Ultimately, the responsibility for individual safety still resides with the public user and their prudent use of Channels. Public users of Channels can include general observers along the bank, recreational enthusiasts in river craft such as rafts and kayaks, fishermen, waders, and swimmers. There may also be occasions where people accidentally fall into the water. Users of Channels also include personnel maintaining or operating various structures and facilities on or adjacent to Channels. 7.2 STRUCTURE SAFETY The design of structures must consider safety of flood control workers and the general public, especially when multiple uses are intended. Regulations and interpretations vary from community to community and may change with time. There are inherent safety risks in any waterway that have to be recognized by the public, designers, emergency responders, and government officials. General suggestions are given in regard to safety and hazard reduction; however, the designer must use a reasonable standard of care for the particular structure being designed or retrofitted that includes evaluation of present or likely future public access and uses such as recreation. It is often reasonable to retain a whitewater boating specialist to assist in the design of a structure in a Channel where public users are present. In general, personal safety risks related to structures in and around Channels include drowning, death, injury, and infection. These risks are primarily related to: Overly retentive submerged hydraulic jump ( Keeper ) Impacts, blunt trauma, and abrasion Foot or extremity entrapment Pinning or entrapment against an obstruction Lack of egress out of the Channel Entrapment or entrainment into structures, gates, screens, etc. SEPTEMBER 30, 2008 CH13-702

4 Channels and rapids, with or without manmade structures are inherently dangerous. A primary objective in the planning, design, and construction of structures is that: Structures be designed and constructed so that they are predictable and without hidden or unobvious hazards to responsible users Meeting this objective allows the ultimate responsibility for individual safety to reside with the boating public and their prudent use of Channels. 7.3 BOATABLE CHANNELS Channels that are known to be boatable, either now or in the future, and those others that are classified by the Colorado Water Quality Control Commission for Class 1 or 2 Recreation, but are not presently judged to be boatable, should have structures designed with public safety as a special consideration and are herein referred to as Boatable Channels. Boatable Channels provide enjoyment to a wide variety of public users Designs for structures within Boatable Channels, including but not limited to: drop structures, control structures for diversions, grade control structures, or lowhead dams, drops or features which form holes or waves, (collectively referred to as Drop Structures); whitewater recreational areas or play parks; recreational inchannel diversions (RICDs); recreational whitewater features; bridge piers, bank armoring; jetties, bendway weirs, fish passages etc.; have to avoid the development of overly retentive hydraulic jumps, sharp edges, foot entrapments, restricted egress, and address those dangers listed in Section 7.2 above. SEPTEMBER 30, 2008 CH13-703

5 Drop Structures in boatable channels should incorporate a boat chute or otherwise include passage for boats designed in accordance with carefully planned components that are consistent with recreational requirements for boater safety. Warning signs and portage routes around such structures are also recommended. 7.4 STRUCTURE INTEGRITY AND PREDICTABILITY Structures in Boatable Channels should be designed to be predictable. Structures which experience movement or failure can create hazardous and/or unpredictable hydraulic conditions. Typically, structures within a Boatable Channel should withstand stream forces for all flows up to and including the 100-year flood. Alternatively, structures can be configured and maintained such that movement of portions of the structures (such as boulders) can be repaired after a high flow event. In the case of river reaches, which historically sustain extended durations of high flows (over weeks), this alternative approach is not practical. All recreational structures, whether public or private, particularly those designed in this alternative manner, should have established inspection and maintenance programs supported by appropriate long-term reliable funding sources and budgets. The same general criteria applied to levees for certification of integrity and safety could be applied recreational structures as well. 7.5 CRITERIA FROM SECTION 6 DROP The design of structures in rivers and waterways which are intended to create a hydraulic jump or wave or hole features are essentially Drop Structures and shall be designed in accordance with appropriate criteria and procedures established in Section 6 of this Chapter. This includes, but is not limited to: Provisions for an effective seepage cut-off to prevent piping and structural instability Hydraulic analysis Rock and armoring sizing Analysis of uplift and seepage Scour and energy dissipation basin development Structural stability and hydraulic forces Avoidance of adverse impacts to the regulatory floodplain Conveyance of sediment and cobble (Bedload) without creating adverse impacts to the river or its floodplain. Allowances for the passage of fish where appropriate 7.6 HAZARD REDUCTION FOR DROP Introduction This section outlines some specific approaches and guidelines that have been used in past design efforts to reduce hazards of boatable drops as SEPTEMBER 30, 2008 CH13-704

6 listed in 7.2 above. Design approaches and guidelines are limited to suggestions for experienced and qualified professional engineers. These are not the only approaches available to the engineer and do not include all issues. Design by an engineers experienced with previous constructed projects, hydraulic modeling, scour analysis, and floodplain regulations is required. Usually the engineer is required to have a valid professional license in the State of Colorado, and follow the Bylaws and Rules of the State Board of Licensure for Professional Engineers and Professional Land Surveyors. Design for Drop Structures which are intended to provide specific recreational attributes such as required for freestyle kayaking, slalom kayaking and canoeing may not follow some of these approaches outlined below in Basic Hydraulic Design Considerations 1. Select maximum hydraulic drop of individual drops generally 1 to 4 feet. If they are more than 4 feet, a physical hydraulic model may be necessary. 2. Determine the type of structure and passage to be used. Be award that boatable structures can significantly increase the cost of the project to improve safety of river passage. Structure selection may be based upon costs, aesthetics, floodplain issues, sediment transport, and river morphology. These types include: a. Full River Passage. An entire structure or series of structures that span the entire channel width and are boatable or passable throughout a range of flows as in Glenwood, Avon, Steamboat, at Union Avenue in Englewood, and most Drop Structures and RICDs that have been created primarily for recreational uses. b. Bypass. A boatable bypass around the Drop Structure such as at Confluence Park in Denver. c. Boat Chute. A localized passage through the dam such as at Alameda Avenue in Denver and at numerous locations along the Platte River through the Denver Metropolitan area. Often the dam is designed or modified with steps or other measures to reduce hazards associated with incidental passage. The stepped dam at Confluence Park is a successful example of this type of hazard reduction. SEPTEMBER 30, 2008 CH13-705

7 This constructed low-head drop structure has a 10:1 downstream slope and a boat chute for enjoyable recreational boating. 3. Determine basic drop characteristics to be compatible with public safety and recreational boating. Suggestions are as follows: a. Use a Froude number, F r, less than 1.5 at the toe of the drop. b. Avoid overly retentive hydraulics throughout the anticipated range of flows up to high flow conditions such as the 10-year event. c. Assess stability of the structure taking into account expected downstream channel degradation. d. Consider the slope of the downstream face of a sloping drop; 10(H) to 1(V) is common. This is particularly relevant to higher flow conditions. e. Provide features to identify locations of passage often pilot rocks, signs, or buoys can be used. f. Provide for energy dissipation downstream of the structure while maintaining structural stability of the drop structure, adjacent banks and adjacent structures such as bridges. Note that local scour depths downstream of various structures have been observed to be over 10 feet. g. Provide portions of smooth invert particularly toward the center of drop(s) to reduce abrasions and the potential for foot entrapment while providing areas of irregularity and SEPTEMBER 30, 2008 CH13-706

8 7.7 WARNING SIGNS COLORADO interstitial flow particularly along the banks for fish passage where fish passage is of concern. h. Provide fish passage and consult with fisheries experts when fish habitat and passage is of concern. i. Incorporate features to address sediment transport, and other dynamic river processes. j. Provide a recovery pool of sufficient length downstream of each drop or a series of drops to allow for recovery of boaters that have capsized or otherwise lost control. The recovery pool should include velocity breaks such as eddies along the banks. k. Provide an upstream cut-off wall to provide for seepage control and to limit piping of the sub-grade l. Provide eddies and armoring to support ingress and egress over a wide range of flows. m. Consider the addition of deadman anchor points located near drop structures for use by emergency personnel so they have something to connect onto during rescues. 4. Obtain peer review on the preliminary design. 5. Provide inspection during placement of rock and features so as to reduce sharp edges and poor local hydraulic conditions. 6. Allow for follow-up adjustment ( tuning ) after completion. Typically this would be conducted during or after construction or within the first year of operation. Signage should be provided at locations where public use is intended near hydraulic structures and where hazards are not obvious to the average person. Warning signs for dams that are to be avoided (i.e. having no passage) is critical and there are a number of examples and guidelines across the United States. However, there are no known standards for warning signing at man-made whitewater park courses or boatable Drop Structures. One of the primary safety problems at various whitewater parks, boatable Drop Structures and natural rapids is the prevalence of users without life jackets. Signage should emphasize the need for life jackets and appropriate safety equipment. Some examples and suggestions from existing whitewater parks and various entities include signs that: SEPTEMBER 30, 2008 CH13-707

9 1. Emphasize the need for life jackets and appropriate safety equipment. 2. Provide information on put-in and take-out locations; 3. Give emergency contacts and phone numbers; 4. Post warnings concerning in-stream risks and hazards; 5. Inform potential users about the difficulty of particular river reaches, based on standard international classifications; 6. Be positioned so as to be observable throughout normal flood flows. 7. Be of permanent design and maintained; 8. Be placed upstream and adjacent to in-stream Drop Structures and recovery pools. 9. Be bilingual or include symbols. Signage wording should be reviewed by legal council and possibly communication/signage experts. Some considerations for wording include: Warning: Strong Currents And Undertows Life Jackets Required (or) Wear Properly Sized Life Jackets At All Times Helmets and Cold Water Clothing Are Strongly Recommended Emergencies Call 911 (and/or provide phone number of fire department) Rapid Ahead - Scout Before Using (The Upstream Sign) Skill Required Paddle Responsibly Bank Drops Off Quickly Boating alone is not recommended Keep Children Under Direct Adult Supervision At All Times Drownings Have Occurred At This Site Even At Low Flows Other statements particularly on the large signs could also include: statements referring to trash, no glass containers, dogs, respect for other users, hours, etc. SEPTEMBER 30, 2008 CH13-708

10 7.7.1 Warning Symbols & Sign Examples Various symbols and signs used at other sites are shown below. General Warning: Life Jacket: SEPTEMBER 30, 2008 CH13-709

11 Clothing: Strong Currents: This could be modified to include wording such as: Recirculating currents prolong swimming distance and may draw you under the water. Portage: SEPTEMBER 30, 2008 CH13-710

12 7.8 PORTAGES & ACCESS Low-head dams not designed for boat passage or other dangerous obstructions should have accessible pathways around the dam or obstruction (Portages). Portages around Drop Structures (with or without boating provisions) should also be provided as flow conditions, the presence of debris, and the skill of users vary. Portages should include a well designed take-out with slow velocities such as an eddy - throughout the normal range of flows and be positioned at appropriate locations. The take-out should be located sufficiently upstream of the structure or obstruction and be combined with suitable signing. The take-out(s) should be designed to resist local scour. Requirements for ADA access should be reviewed. Egress access along at least one bank and preferably both banks should be provided upstream and downstream of a Drop Structure. Downstream access should include a recovery pool (or series thereof) to provide for egress out of the water. Again, requirements for ADA access should be reviewed. Jetties can provide slow currents for access and portages as well as provide bank stabilization benefits. 7.9 OTHER CONSIDERATIONS Considerations beyond overly retentive hydraulic formations (Keepers) to reduce hazards listed in 7.2 above include: 1. Sharp Edges. Avoid sharp edges and protruding objects. 2. Intakes and Screens. Screen water intakes (headgates) and avoid approach velocities into these intakes greater than one-half to one foot per second. 3. Utilities and Apparatus. Provide physical separation, barriers, warning buoys & signs with hydraulic grates or screens, sluice gates, etc. SEPTEMBER 30, 2008 CH13-711

13 4. Fish passage. Provide for fish passage when appropriate. Determine favorable current patterns and criteria related to behavioral patterns of the target species. Determine maximum sustained and darting velocity criteria of target species, and model to meet criteria. Provide for effective attractive velocity filaments and avoid dead-ends so as to guide fish to the passage locations. 5. Bridge Piers. Reduce the chances for pinning or wrapping on bridge piers or other obstructions by creating appropriate hydraulic conditions. Piers can be made safer with debris walls and with the correct alignment to the river. Clear span bridges are certainly preferable, but may be cost prohibitive. Attempts should be made to keep piers out of the floodway and main channel corridor. Often two piers, one at each bank, are preferable to one pier in the center of the channel. However, caution is needed during the design since even piers located at the toe of the bank can be a hazard and may trap rafters between the bank and pier. 6. Emergency Rescue Provisions. Provide suitable access for use by rescue personnel. 7. Bicycle and Pedestrian Paths. Provide adequate directional and warning signs, sight distance, and avoidance of unannounced sharp turns and dropoffs when bicycled and pedestrian paths are located adjacent to structures, separate paths or trails for in-river users (generally lower in elevation) and bicycle traffic when practical RETROFITTING EXISTING The need to retrofit low-head dams and Drop Structures to provide Portages and in-river passage with chutes or a bypass is discussed above. Generally retrofitting these structures includes installing a stepped or sloped downstream surface along the downstream face of the dam or Drop Structure and providing appropriate barriers, signing and accessible portages with take-out and put-in landings. It can also include the addition of a boat chute or bypass to allow for passage of appropriate river craft. A structure that is too high for the site may be replaced with two or more structures to reduce the drop at a single location. Retrofitting or replacing exiting structures with less than 1.5 feet of hydraulic drop has been necessary to reduce hazardous hydraulic conditions. Retrofitting low-head dams or Drop Structures requires specific care to insure that the retrofit meets the objective of enhancing public safety. Due to specific site and structure conditions, physical hydraulic models are common in the design phase for retrofitting of low-head dams and Drop Structures. SEPTEMBER 30, 2008 CH13-712

14 7.11 IN-CHANNEL DIVERSIONS (RICDS) Introduction and CWCB s Role Colorado is one of the few states that statutorily recognizes "recreational in-channel diversion" (RICD) water rights. In response to requests for water rights associated with the protection of water for recreational purposes, the General Assembly passed Senate Bill 216 in The bill provided that local governmental entities could apply for water rights for recreational in-channel diversions ("RICDs"), but limited these types of water rights to the "minimum stream flow for a reasonable recreational experience in and on the water." In 2006, the General Assembly passed Senate Bill 37, which focused the CWCB s review of RICD applications in three areas: 1. Will the application promote the maximum beneficial use of water? 2. Will the application impair Colorado's ability to fully develop its compact entitlements? 3. Will the application adversely impact CWCB instream flow water rights? Section , C.R.S., requires applicants for recreational in-channel diversion water rights to provide a copy of their application to the Colorado Water Conservation Board for review. The CWCB then provides findings to the water court after deliberation in a public meeting. The water courts must consider the CWCB findings. The water courts must also consider whether the water right sought is: 1. The minimum necessary for a reasonable recreational experience; 2. Whether or not the RICD is accessible; 3. Whether or not the RICD is an appropriate stream reach; The size and magnitude of flows protected by many of these RICD water rights to date have the potential to restrict future upstream development potential and may reduce the flexibility that Colorado has to manage its water resources. The RICD legislation is relatively new and may be subject to further legislation and court challenges. SEPTEMBER 30, 2008 CH13-713

15 Adverse Floodplain Impacts and Durability The CWCB takes very seriously the flood safety aspects of RICDs, and will carefully consider flood safety in reviewing the RICD application and in providing information to the court on whether the RICD is an appropriate stream reach. The CWCB recommends that an applicant for an RICD demonstrate, through appropriate technical analyses, the proposed boating course is designed and will be (is) constructed in such a manner as to: Adequately pass all flows up to and including the 100-year (1% probability) flood flow without causing adverse impacts to upstream, downstream or adjacent property owners. Verification of no adverse impact can be demonstrated through the use of a CWCB approved step-backwater hydraulics model such as HEC- RAS. Adequately withstand stream forces for all flows up to and including the 100-year flood so that damage and failure of the boating course is avoided Physical Characteristics of an Appropriate Stream Reach In order for the applicant to demonstrate the appropriateness of a proposed RICD stream reach to a water court, the CWCB recommends a minimum average slope of 0.5% for a destination-oriented RICD stream reach based on hydraulic fundamentals and engineering considerations. This suggestion is also based on stream channel information from existing boating courses in Colorado. It is certainly possible that a recreational facility could be constructed on a stream having an average slope of less than 0.5%, depending on the intended use. The designer may choose to incorporate physical features to increase the localized slope and enhance the experience within the RICD stream reach. Such features, however, should not create adverse impacts and should avoid increased flooding conditions as discussed above. Natural stream reaches with inadequate slope can present challenging design considerations for destinationoriented boating facilities, as stream power is an important factor in determining the success of a destination-oriented boating experience. As an alternative to the suggested minimum slope, the applicant may choose to evaluate the appropriateness of the RICD reach by computing a Performance Index (PI). A Performance Index of less than 75 may suggest an inappropriate stream reach for a destination-oriented RICD (see Section below for details related to Performance Index). In the event that the applicant is seeking an RICD for a recreational experience SEPTEMBER 30, 2008 CH13-714

16 other than a destination-oriented boating course, the application will be reviewed accordingly Summary of the Performance Index The Performance Index is a reasonable formula to evaluate whitewater or boating course potential. The Performance Index is a product of the percentage slope and the discharge for the RICD in question: PI=((Hydraulic Drop/Boating Course Length) x Discharge) x 100 Where: Hydraulic Drop and Boating Course Length are measured in the same units (i.e. feet) and Discharge is measured in cubic feet per second (cfs). Hydraulic Drop is the difference (in feet) between the water surface elevation just upstream of the upstream control point and the water surface elevation at the Downstream Section of No Hydraulic Impact. Boating Course Length (in feet) is defined along the RICD stream reach centerline starting at the most upstream control point and continuing through the most downstream control point that enhances and defines the RICD reach. Furthermore, the Downstream Cross-Section of no Hydraulic Impact defines the downstream terminus of the Boating Course Length. The Downstream Section of No Hydraulic Impact is defined as the stream cross-section at (or just downstream of) the RICD reach where river and hydraulic parameters such as velocity, shear stress, channel width, channel depth, sinuosity, etc. are first returned to the pre-project state. The Performance Index has several advantages as it can determine the potential of an undeveloped site and a developed site on an equal basis. It does not rely on subjective judgments regarding the average conveyance width. The Performance Index takes into consideration enhancing hydraulic head by impounding water at the start of the course in order to achieve more drop. The Performance Index can be easily verified by field measurement and by computational hydraulics. A Performance Index of 75 is considered as a minimum threshold of a reasonable recreational experience for a destination-oriented boating course whereas a higher index number such as 500, for example, can be considered to have world class potential. These numeric values reflect the Performance Indices that exist at pay for courses. SEPTEMBER 30, 2008 CH13-715

17 The Performance Index is based on the premise that the course designer can create good recreational conditions by manipulating the hydraulics, geometry, streambed and overbank areas of the stream. For this, the site must have design flexibility, or be readily modifiable to allow design flexibility. Using the Performance Index methodology, a marginal site in terms of flow rates, hydraulic gradient, and site flexibility can be identified and deemed appropriate or inappropriate for an RICD water right. The CWCB does not intend for the Performance Index to be used in evaluating the upper end of potential flow rates requested at a proposed RICD site. The CWCB intends for the Performance Index to be used to evaluate the appropriateness of a specific stream reach for a proposed RICD water right Flow Rate Guidelines for an RICD The CWCB recommends that an RICD Flow Rate appropriate for a particular recreational facility be based upon characteristics of the stream reach, site, intended use, and efficient use of the flow. The basis for filing for a water right of, for example, 1800 cfs, should not be arbitrary. Computations should be done to justify the applied for flow rate. Computations should include at least two-dimensional computer models and/or physical modeling. Modeling should include the effects of longterm sediment deposition. Determination of the intended recreational experience throughout the requested flow range should be made. This may be based upon a user survey, economic analysis, or other appropriate means. Once completed, the intended hydraulic formations must be described and criteria formulated. Hydraulic modeling combined with design experience should be completed to determine that the various hydraulic features are created with the minimum flow necessary to create the intended hydraulic formations. Velocities, wave heights, hydraulic jump characteristics, eddy patterns, and the various depths and hydraulic profiles should be accurately and quantitatively described so that once constructed, it can be determined that the RICD is performing as intended throughout the requested range of flows. Senate Bill 37 also provided specific statutory guidelines for the time periods, flow rates, and number of flow rates permissible for an RICD water right. Any RICD must comport with the statutory requirements. SEPTEMBER 30, 2008 CH13-716

18 Hydraulic Engineering Definition of Control A recreational whitewater boating course must include manmade hydraulic stream features that provide control of the entire RICD streamflow as required by engineering principles. The hydraulic engineering definition of control is a section across the stream where a manmade structure causes the flow to pass through critical depth when flow changes from subcritical to supercritical flow. The phenomenon gives rise to what is known as a control section. Control of the entire flow should occur and be effective within the river cross-section of interest for each RICD flow rate requested by applicants. The CWCB's definition of hydraulic control applies to each structure within an existing or proposed stream reach that is the subject of an RICD water right. Hydraulic structures should capture and control the entire streamflow for the RICD flow rate, or range of flow rates, requested by the applicant. An upstream seepage cut-off wall to control seepage, underflow and the loss of surface flow should be constructed into each drop structure. Analysis to demonstrate that seepage under the structure is limited below that flow which would create piping or uplift of the structure. For example, if a proposed RICD stream reach is 900 feet long and contains 7 hydraulic structures, each of the structures must independently capture and control the RICD streamflow for the intended recreational use. The CWCB suggests that an inconsistency with requirements of SB would result from the inability of a hydraulic structure to adequately capture and control the entire RICD flow rate Design, Documentation and Record Drawings. Design should follow the recommendations outlined in this Section and applicable portions of this Chapter 13. Design drawings should allow for the determination of the grade and construction material at any point of the proposed structures. Drawings should be as-built so that any future repairs can return the structure(s) to their original configuration. All calculations and survey information should be provided so as to allow for the review of design and determination that the features were designed to require the minimum amount of flow for the intended use and specific indented hydraulic formations throughout the requested flow ranges Liability The CWCB assumes no responsibility for use or misuse of the boating course and is not subject to liability for injuries or damages caused by them. The CWCB s approval of or recommendation to endorse an applicant s proposed RICD water right in no way implies that the CWCB accepts responsibility for final design, construction, operation, and safety of the boating course. SEPTEMBER 30, 2008 CH13-717

19 7.12 GLOSSARY OF RELATED TERMS Term or Abbreviation Aggradation Bed load CFS Degradation Drop Structure Eddies Flood Recurrence Freestyle Gradient Hole(s) Meaning Raising of river bottom by deposition of sediments Coarse sediment transported along the bottom of the river by sliding, hopping, etc. Cubic Feet per Second--measure of discharge or flow Lowering of river bottom by net removal of sediments A constructed feature or structure in a Channel that creates a downward step in the water surface and a resulting hydraulic jump downstream of the structure. These can typically have a hydraulic drop of one-half to eight feet. These structures can be used for a number of purposes including diversions, recreation, and river stability. They can be called control structures, diversions, grade control structures, low-head dams, weirs, or just drops. They have been constructed of boulders, concrete, steel, wood, and plastic. Eddies are usually formed downstream an obstruction or curvature in a river or channel. Eddies swirl on the horizontal surface of the water. Typically, they are areas where the downward movement of water is partially or fully arrested and currents flow in an upstream direction - a nice place to rest or to make one's way upstream. The statistical probability of a particular flood level occurring within a specified time period, e.g. one year, five year, 100 year. Competitive event where boaters perform tricks on a wave or hole. The ratio of vertical drop to horizontal run, expressed in terms of percentage slope. Holes, are formed when water pours over a submerged structure causing the surface water to flow back upstream toward the object. In hydraulic design terms, it is a particular formation of a hydraulic jump. (See below.) In the design of man-made whitewater or other structures within a river or waterway, it is usually created by a drop structure or structure(s) which create a significant constriction in the channel.. Holes can dramatically aerate the water, possibly to the point where it may even lose the capacity to carry any water crafts. Overly retentive holes or keepers (see below) can be dangerous as a boater may become stuck in the recirculating water. Holes in recreational structures are intended to be entertaining play spots, where paddlers use the holes' features to perform various play boating moves. Some of the most dangerous types of holes are formed by low-head dams (weirs), underwater ledges, and similar types of obstruction. In low-head dams, the hole has a very symmetrical character - there's no weak point - and where the sides of the hydraulic are often blocked by a man-made wall, making it impossible to slip off the side of the hydraulic. Low-head dams are insidiously dangerous because their danger cannot be easily recognized by people who have not studied whitewater SEPTEMBER 30, 2008 CH13-718

20 Hydraulic Hydraulic Drop Hydraulic Jump Invert Keeper or Overly Retentive Hydraulic Play boating Pillows Sediment Slalom Suspended load Thalweg Wave(s) A hydraulic can refer to a hole or wave see below. The technical term is a hydraulic jump, although it could also be used to describe a hydraulic formation known as a supercritical shock wave. Sometimes referred to as just drop. The vertical distance between the upstream and downstream water surface elevation. This can be applied to a single feature or to multiple features within a river reach or whitewater course. A hydraulic transitional formation that occurs between supercritical and subcritical flow. This occurs downstream of a Drop Structure when the fast flow collides with the slower moving flow in a downstream pool. It is the commonly referred to by river recreationalists as a hole, wave, or hydraulic. The bottom of a Channel. A hydraulic condition technically a specific form or a hydraulic jump that can occur below a natural or man-made feature (such as a low-head dam) that tends to trap boaters, swimmers, or other floating objects for an extended length of time. Can also be called a roller, reverse roller, hole, or drowning machine. Recreational boating primarily for surfing and performing tricks on waves or in holes Pillows are formed when a large flow of water runs into a large obstruction, causing water to "pile up" or "boil" against the face of the obstruction. Pillows are also known as Pressure Waves Mineral particles of varying sizes transported by a river Competitive event where boaters negotiate gates suspended over the river for the fastest time Fine sediment suspended in moving water Deepest portion of the invert in a Channel Waves are formed in a similarly to holes and are sometimes considered hydraulics as well. In hydraulic design terms, it is a formation of a hydraulic jump which is created downstream of a supercritical reach of flow. In the design of man-made whitewater or other structures within a river or waterway, it is usually created by a drop structure or a structure which creates a significant constriction in the channel. Waves are noted by the large smooth sloping face on the water green water at the upstream portion of the formation followed by a crest and downward sloping face. A wave can have a significant amount of whitewater or haystack and appear similar to a hole. These are called breaking waves. Sometimes a particularly large wave will also be followed by a "wave train", a long series of waves. SEPTEMBER 30, 2008 CH13-719