Planning and Layout 

of Small-Stream 

Diversions

FOREST SERVICE

D E P A RTMENT OF AGRICU L T U R E

United States Department of Agriculture

Forest Service

National Technology & Development Program • 2500—Watershed, Soil & Air Mgmt • 1325 1801—SDTDC • March 2013
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PLANNING AND

LAYOUT OF SMALLSTREAM DIVERSIONS

by

Dan S. Axness

McMillen LLC, Boise, ID

with

Kim Clarkin

San Dimas Technology and Development Center, 

San Dimas CA

v

Acknowledgements ........................................................................................................................... vii

Chapter 1—Introduction

1.1 Purpose of the guide .............................................................................................................. 1

1.2 Anatomy of a diversion........................................................................................................... 3

1.3 Why are we concerned about diversions? ............................................................................. 4

Chapter 2—Site Assessment and Objectives ................................................................................. 15

2.1 Step 1: Background information........................................................................................... 16

2.2 Step 2: Evaluate existing conditions and identify site constraints ........................................ 18

2.3 Step 3: Survey the site ........................................................................................................ 22

2.4 Step 4: Set objectives........................................................................................................... 29

Chapter 3—Headgates ...................................................................................................................... 35

3.1 Headgate types .................................................................................................................... 36

3.2 Headgate sizing ................................................................................................................... 44

Chapter 4—Diversion Structures: Weirs, Pumps, Infiltration Galleries

4.1 Weirs .................................................................................................................................... 45

4.1.1 Types of check structures ........................................................................................ 55

4.2 Pump stations....................................................................................................................... 87

 4.2.1 Types of pumps........................................................................................................ 91

4.2.2 Pump operation and maintenance ........................................................................... 92

4.3 Infiltration galleries ............................................................................................................... 93

4.3.1 Infiltration gallery operation and maintenance ......................................................... 96

4.4 Toxic materials...................................................................................................................... 96

4.5 Diversion structure applicability............................................................................................ 97

Chapter 5—Fish Protection at Diversions

5.1 Fish screens and fish screen bypass systems................................................................... 105

5.1.1 Fixed-plate screens.................................................................................................110

5.1.1.1 Cleaning systems for fixed-plate screens...................................................112

 5.1.2 Moving screens.......................................................................................................114

5.1.3 End-of-pipe screens................................................................................................117

Table of Contents
vi

Planning and Layout of Small-Stream Diversions

 5.1.4 Screen comparisons ...............................................................................................117

 5.1.5 Common causes of screen failure.......................................................................... 123

5.1.6 Fish-screen bypasses ............................................................................................ 123

5.2 Upstream fish passage....................................................................................................... 124

5.2.1 Relocating the diversion......................................................................................... 124

5.2.2 Seminatural, open-channel fishways designed for a target fish............................. 126

 5.2.3 Fish ladders............................................................................................................ 127

5.2.3.1 Denil and Alaska steep-pass fish ladders ................................................. 127

5.2.3.2 Pool-and-weir fish ladders......................................................................... 128

5.2.3.3 Vertical-slot fish ladders ............................................................................ 130

Chapter 6—Flow Measurement...................................................................................................... 133

6.1 Sharp-crested weirs ........................................................................................................... 135

6.2 Measuring flumes............................................................................................................... 138

6.3 Submerged orifices ............................................................................................................ 143

Chapter 7—Operations, Monitoring, and Maintenance Plan....................................................... 147

Glossary/Bibliography .................................................................................................................... 153

Appendix A—Site Assessment Checklist ..................................................................................... 159

Appendix B—Automating River Diversions.................................................................................. 167

SCADA systems for diversions.................................................................................................. 169

Constraints for automation and SCADA systems...................................................................... 174

References................................................................................................................................ 177
vii

Acknowledgements

This guide owes its existence to Dave Gloss, hydrologist on the Medicine 

Bow National Forest. In 2006, as a result of his work with irrigation 

diversions and their effects, he suggested the need for a technical 

guide to structures “capable of achieving desired stream flows below 

diversions.” The guide attempts to accomplish that objective by sharing 

experience with the diversion components that can, when properly 

designed and managed, regulate flows and protect stream and riparian 

resources. Other people with years of experience in diversion design 

also saw the need and engaged in the project. Rob Sampson and 

Clare Prestwich (U.S. Department of Agriculture, Natural Resources 

Conservation Service [NRCS]); Jeanine Castro (U.S. Department of the 

Interior, U.S. Fish and Wildlife Service); and Bob Kenworthy and Tim 

Page (U.S. Department of Agriculture, Forest Service) helped define 

the initial focus and organization. Rob Sampson’s review improved the 

guide’s handling of “nature-like” versus hydraulic design. Clare Prestwich 

coauthored appendix B, with additional help on that appendix from 

Stephen Smith and Peter Robinson. Kozmo Ken Bates also offered 

perspective on common diversion problems. 

The following people responded to questions or helped improve the draft 

by reviewing and critiquing it:

Jeanne Rumps, Idaho Department of Fish and Game

Jean Thomas, National Water Rights and Uses 

Mark Moulton, Sawtooth National Recreation Area

Bob Kenworthy, Tim Page, and Jim Nutt, Intermountain Region 

Adjudication Team 

Bill Goodman, Intermountain Region Watershed Program

Christine Dingman, Ashley National Forest 

Charles Condrat, Wasatch-Cache National Forest

Dave Gloss, Medicine Bow National Forest

Kathryn Boyer, NRCS West National Technical Support Center

Warren Colyer, Trout Unlimited

Rob Sampson, USDA NRCS, Idaho

Clarence Prestwich, USDA NRCS, Portland

Morton D. McMillen, McMillen LLC

Stephen W. Smith, Regenesis Management Group

Stan Bradshaw, Trout Unlimited

Peter M. Robinson, NRCS West National Technical Support Center
viii

Planning and Layout of Small-Stream Diversions

We are very grateful to those who contributed illustrations:

Christine Dingman, Ashley National Forest

Mark Moulton, Sawtooth National Recreation Area

Kathleen Frizel, Bureau of Reclamation

Jim Nutt, Intermountain Region, Instream Flow Program

Anne Marie Emory Miller, Henry’s Fork Foundation

Darrin Miller, U.S. Geological Survey

Warren Colyer, Trout Unlimited

Kozmo Ken Bates, Engineering Consultant, Olympia, WA

Matt Woodard, Trout Unlimited

Brian Hamilton, Bureau of Reclamation

Roger Ford, USDA NRCS, New Mexico

Graphics by Deborah Mucci, Forest Service, National Technology and 

Development Program, and Gerald Gregory.
1

Chapter 1—Introduction

Many surface water diversions are located on streams within the 

boundaries of the National Forest System of the Forest Service, an 

agency of the U.S. Department of Agriculture. These diversions serve 

many different uses, including crop and pasture irrigation; single home, 

tract, industrial, or municipal water supply; and hydropower. They are one 

part of our infrastructure that increasingly is stressing aquatic populations 

and habitats (Northcote 1998). To help protect stream ecosystems, 

more efficient water management and more attention to aquatic species 

passage at surface water diversions are becoming critical. 

This guide serves as a reference for Forest Service personnel and water 

users evaluating options for diversion infrastructure and management on 

streams less than about 50 feet wide. Topics include layout, operation, 

and maintenance of structures for water diversion; water control and 

measurement; and structures for fish protection (fishways, ladders, 

screens). We will describe the pros and cons of different structure types, 

their maintenance requirements, relative construction costs, and common 

failure modes. The guide should give Forest Service field staff and water 

users the information they need to plan diversion systems that meet 

users’ water needs while protecting aquatic and riparian habitats and 

organisms to the greatest possible degree. 

Figure 1.1—Jerry Bird, Forest Service Intermountain Region Ditch Bill program 

manager, and Peter Frick, diverter, discussing an existing diversion and possible 

upgrades. Wise River Ranger District, Beaverlodge National Forest, 2009. 

1.1 Purpose of the guide

Chapter 1—Introduction
2

Planning and Layout of Small-Stream Diversions

Forest Service staff should keep in mind that diversions entail several 

levels of authority and responsibility, both private and governmental. 

In the West, the water-rights holder, the local water master, and the 

State water resources agency are always involved. Other State and/or 

Federal regulatory and land management agencies may be involved, 

depending on the diversion’s location. For example, State wildlife 

management authorities; U.S. Department of the Interior, U.S. Fish and 

Wildlife Service; and U.S. Department of Commerce, National Oceanic 

Atmospheric Administration, National Marine Fisheries Service may all 

have authority in different situations. 

Western State water laws provide water-right holders with a right to 

divert water in priority. Western water laws do not, however, provide 

access to the water with the water right. Rather, access to the water 

across the land of another is provided under State realty laws. In the 

case of Federal lands, access can only be provided under Federal law. 

Federal laws may mandate the imposition of terms and conditions to 

protect the Federal estate, including the aquatic and riparian resources 

and their dependent wildlife, such as fish, amphibians, and other aquatic 

species. 

It has long been Forest Service policy that special use permits 

authorizing water diversion facilities located on National Forest System 

lands incorporate stipulations to protect aquatic habitat and/or maintain 

stream channel stability (Witte 2001). In fact, the Forest Land Policy 

and Management Act of 1976 requires such stipulations. The act states 

that before issuing an authorization for facilities to impound, store, 

transport, or distribute water on public lands, the Forest Service and 

U.S. Department of the Interior, Bureau of Land Management must 

impose terms and conditions that...”minimize damage to scenic and 

esthetic values and fish and wildlife habitat and otherwise protect the 

environment” (43 U.S.C. 1765). In addition, the Endangered Species 

Act requires Federal agencies to ensure that any action they authorize 

“...is not likely to jeopardize the continued existence of any endangered 

species or threatened species or result in the destruction or adverse 

modification of [designated critical] habitat.”

Diversion structures change the nature of a stream by ponding and 

diverting some water. Ideally, they are designed to remove water from 

the channel while passing sediment, woody debris, and fish beyond 

the structure. Most structures are effective in removing water, but they 

occasionally block sediment movement, accumulate debris, block fish 

passage in the main channel, entrain fish in the diversion ditch, or 

dewater the stream entirely.
3

Chapter 1—Introduction

Forest Service staff and water users can use this guide to assess 

existing diversions, identify problems at a site, and identify possible 

types of structural and operational improvements that might solve 

those problems. The guide is intended to facilitate interactions with a 

professional engineer/designer by familiarizing readers with diversion 

components and issues. It is not a substitute for an engineer experienced 

in diversion design. Diversions that provide the appropriate amount of 

water without burdensome operation and maintenance requirements 

AND adequately protect the aquatic system will almost always require 

design tailored to the site by an experienced engineer. 

Diversions are comprised of some combination of the following (figure 

1.2):

■ Diversion structure (e.g., dam, weir, and so forth).

■ Headgate, pump, or other water intake structure. 

■ Ditch or pipe conveying diverted water to the point of use.

■ Fish screen and bypass channel returning fish to the stream.

■ Fishway for upstream fish passage.

■ Water measurement (and sometimes recording) device.

Where the control structure is located down-ditch (common, particularly 

in older structures), a wasteway channel is often included through which 

surplus water is returned to the source. 

Figure 1.2—Typical layout and components of a diversion. This drawing 

demonstrates how the various parts of a diversion are located and related to 

each other. Not every diversion has all components. 

1.2 Anatomy of a diversion
4

Planning and Layout of Small-Stream Diversions

In this guide, chapters 3 through 6 provide an overview of the common 

types of all of these components, the benefits and disadvantages of 

each, and sites or situations where each might best be used to limit 

detrimental effects on the aquatic environment. This information should 

help identify the best options for individual sites. Chapter 7 provides an 

overview of operations, monitoring, and maintenance actions commonly 

associated with diversion structures.

Chapter 2 describes the first steps in planning for new or upgraded 

diversions. These steps include gathering historical and environmental 

background information about the site and evaluating current conditions 

and problems. 

Many diversions on National Forest System lands have been in place for 

decades and are still using manual techniques for water control. Many 

are in remote locations where headgates—if they exist—may or may not 

be adjusted in response to changing runoff, and ditch failures may not 

be noticed for days or weeks. Some diversions take water from streams 

with threatened and endangered species, and effects on the aquatic 

system are of high concern for that reason. 

Diversions that are not well designed and operated can damage 

streams, aquatic and riparian habitats, and aquatic organisms in very 

important ways. None, one, or any combination of the following types of 

effects may be important at any specific site.

■ A diversion dam backwaters streamflow and can cause sediment 

deposition, especially if the dam is not removed or if sediment is not 

sluiced during high flows (figure 1.3). Upstream of the dam in the 

depositional area, the stream may be locally shallower and more 

prone to flood adjacent lands. The riparian water table may be higher. 

This could have two different effects: it could lengthen the duration of 

saturated, anaerobic conditions in the root zone, stunting growth, and 

diminishing the vitality of the riparian vegetation; or it could improve 

water availability, increasing the vigor of riparian vegetation (Bohn 

and King 2000). Local streambed material may be finer and more 

uniform than in the undisturbed channel, burying diverse, formerly 

aerobic habitats. In unentrenched reaches, where streambanks are 

not heavily vegetated, or where riparian shrubs have lost their ability 

to armor the banks, the channel may widen and/or shift position 

across the valley floor. 

1.3 Why are we concerned about diversions?

Stream channel 

morphology and stability
5

Chapter 1—Introduction

Figure 1.3—Santa Margarita River O’Neil diversion weir at Camp Pendleton, 

CA. This steel pile dam is in a river with very high sediment load. Heavily 

vegetated sediment accumulations upstream and downstream are visible in 

this photo, which was taken shortly after a moderate flood had disturbed the 

channel. Photo by Kathleen Frizel, Bureau of Reclamation. 

■ Streambed scour caused by water plunging over the dam crest 

(figure 1.4) can undermine and destabilize a poorly built dam. If the 

downcutting destabilizes the dam (for example, a nonengineered 

dam built of streambed materials) and a zone of channel bed erosion 

migrates upstream as a headcut, the dam and diversion inlet also 

must be moved upstream. In some cases, this has occurred many 

times, as the water user seeks the elevation needed to allow gravity 

flow into the ditch. Bates (2006) identified this as a relatively common 

reason for stream-reach dewatering in the Sawtooth National 

Recreation Area, and recommended that points of diversion be 

moved downstream where possible. 
6

Planning and Layout of Small-Stream Diversions

Figure 1.4—Concrete diversion dam on Archie Creek, Boise National Forest, 

ID. The substantial (approximately 5 foot) downcutting caused by the dam on 

this small, steep stream can be seen beyond the dam in the distance, and in the 

inset. Plastic sheeting seen on the right bank is a temporary fix for the soil piping 

that, if left unchecked, will undermine the dam. 

■ Where heavy equipment is used to rebuild push-up dams annually 

from streambed material, the repeated disturbance increases 

sediment loading to downstream reaches and disrupts local 

streambed structure (figure 1.5). This can damage channel bed 

stability, water quality, and aquatic habitat. 
7

Chapter 1—Introduction

Figure 1.5—Push-up wing dam, Salmon River, ID. Runoff from a wildfire area 

upstream is causing the turbidity here.
8

Planning and Layout of Small-Stream Diversions

■ Dams can be undermined by downcutting or piping, or toppled by the 

pressure of water. Dam failure, together with the headcutting likely 

to occur afterward, can produce enough sediment to affect aquatic 

habitat and water quality for some distance downstream.

■ Summer water temperatures can increase in slow-moving backwaters 

upstream of diversion dams. In the main channel downstream of the 

point of diversion, water temperature can increase dramatically when 

flow is so low that the exposed streambed heats up. 

■ The decrease in instream flow due to water diversion reduces the 

area and depth of instream aquatic habitats (figure 1.6). It may also 

decrease the water available to downstream riparian vegetation, 

potentially affecting its vigor and productivity.

Figure 1.6—(A) Diversion for small hydropower project dramatically reduces 

flow in the channel at the right. Trail Creek, Middle Fork Ranger District, Salmon 

Challis National Forest, 2007. (B) Idaho’s Beaver Creek, dewatered by multiple 

irrigation diversions upstream, August 2001.

A

B

Water and aquatic 

habitat quality at risk
9

Chapter 1—Introduction

■ Where flow into the ditch was not well controlled in the past, there 

are cases where most streamflow now flows in the former ditch and the 

headgate has been moved downstream. This isolates a section of the 

natural channel, leaving it with little or no water at low flows (figure 1.7).

Figure 1.7—Hypothetical history of a poorly controlled diversion. The ditch 

captured the stream when the old headgate failed to prevent high flows from 

entering the ditch. The current stream channel is dry, and all flow is now in 

the former ditch, which is high on the valley sideslope. The current channel 

downstream of the diversion dam is therefore steep and could be impassable to 

fish that might be migrating upstream. 

Aquatic organisms
10

Planning and Layout of Small-Stream Diversions

■ Where high flows are not prevented from entering the diversion ditch, 

the ditch may overtop and breach. This also can occur when debris 

obstructs the ditch or the ditch bank ruptures and is not noticed in time. 

Where the ditch runs along the valley sideslope, such a breach can 

cause gullying and landsliding (figure 1.8). 

Figure 1.8—Massive slope failure along diversion ditch. The failure was caused 

by poorly controlled flows at the headgate and debris accumulation in ditch, 

causing the ditch berm to fail by overtopping or percolation through root or small 

animal holes. Soldier Creek, Medicine Bow National Forest, WY. Figure 3.8 

shows the headgate.
11

Chapter 1—Introduction

■ Some diversion dams impede the upstream movement of swimming 

and crawling species (Schmetterling and Adams 2004), preventing fish 

and other aquatic organisms from finding spawning sites, food, refuge 

from warm water temperatures, and so forth (figure 1.9). 

Figure 1.9—This diversion dam was a barrier to upstream passage of fish, 

including the chinook salmon shown here. The dam has since been removed. 

Alturas Lake Creek, ID. 
12

Planning and Layout of Small-Stream Diversions

■ Fish can enter or be swept into the ditch and may be unable to return 

to the main channel (Gale et al. 2008) (figure 1.10).

Figure 1.10—(A) The unscreened Cross Cut Canal in the Henry’s Fork Snake 

River watershed entrains both game and nongame fish. Before the headgate is 

closed at the end of the crop season, the Henry’s Fork Foundation sweeps the 

ditch to salvage fish that would otherwise be stranded. In 2009, 116 rainbow, 

brook, and brown trout as well as 593 whitefish were salvaged from the first 100 

meters below the headgate and returned to the river. (B) Juvenile salmonids 

were entrained in this ditch and stranded when the headgate was closed for the 

season, Salmon River, ID. 

A

B
13

Chapter 1—Introduction

■ Small fish and other aquatic species can be swept onto and pinned 

against the surface of some types of fish screens. Boreal toads, which 

float downstream in summer, have been found dead in front of fish 

screens in Montana (Adams et al. 2005).

■ Fish in the main channel downstream of the diversion can be stranded 

when a headgate is opened if instream water elevations drop abruptly.

Some of the effects discussed above are direct, others are indirect, 

and all may be cumulative. Whether they are important or not depends, 

as always, on the situation. Where adverse effects are important, 

planners should determine what is necessary to protect aquatic and 

other resources, and then work with water users to achieve those goals. 

The diversion may need upgrades to improve water control, water use 

efficiency, or reduce effects on aquatic biota. Within the limits defined 

by Federal law, regulation, and policy, planners should try to optimize 

the Federal terms and conditions granting the access in a manner most 

beneficial for all.

Diversions are more than just the dam or diversion structure. They are 

interrelated systems of structures and management actions. General 

best management practices for protection of water quality at diversions 

and conveyances are outlined in “The Forest Service National Core Best 

Management Practices” (U.S. Department of Agriculture, Forest Service 

2009). Each site, however, will have its own set of stream/site/water user 

characteristics and needs, and best practices will be to some degree site 

specific. Planning the best solution for each site requires understanding 

the aquatic, riparian, hydraulic, and management contexts. Then, an 

interdisciplinary team including the water user can select the structures, 

identify objectives, design the layout, and devise an operating plan that 

achieves the objectives. Again, for most diversions, an experienced 

diversion engineer on the team will be essential. 

Summary

15

Chapter 2—Site Assessment and Objectives

This chapter guides users through a site assessment for evaluating 

diversion condition or considering modifications. The process can be 

broken into the following steps:

1. In the office, gather background information about the site.

a. Historical information about management of the existing 

 diversion and other associated diversions.

b. Aquatic ecology.

 i. Habitats upstream and downstream.

ii. Aquatic species use of those habitats: timing, importance, 

 known issues.

c. Watershed hydrology and land uses (U.S. Geological Survey 

 Stream Stats, impaired water body listing, watershed studies).

d. Projected future changes in water, sediment, woody debris 

 loadings.

2. At the site, evaluate the current condition of the diversion 

installation and the channel. Identify site constraints and 

opportunities. Do this with the diverter, if possible.

3. Survey site topography and hydraulic infrastructure paying 

particular attention to existing water levels and historic 

watermarks.

4. Set objectives for the upgrade. Do this with an interdisciplinary 

team including the diverter and any other interested parties.

The background information (1) places the diversion in its management 

and environmental context. You will need it to interpret what you see in 

the field. It also is needed to develop well-founded objectives for any 

upgrade and to plan a structure that disrupts the aquatic system as little 

as possible. 

The condition assessment (2) identifies and documents observable 

design and operations issues associated with the diversion. The site 

survey (3) produces basic channel data for the area above, at, and 

below the diversion that enables you to envision possible alternative 

improvements and helps in estimating their cost. Diversion structure 

improvements commonly benefit both fish and other aquatic organisms 

and water users, but they may be expensive and require outside funding. 

Together, the site survey and condition assessment can constitute 

documentation for applying for financial assistance for the upgrade, 

Chapter 2—Site Assessment and Objectives
16

Planning and Layout of Small-Stream Diversions

as well as communicating with a prospective engineer/designer. Most 

water users can take advantage of professional engineering design and 

financial assistance from the U.S. Department of Agriculture, Natural 

Resources Conservation Service (NRCS). Conservation district staff and 

qualified consulting engineers also can provide assistance.

In steps 1 through 3, one develops a familiarity with site history, 

resources and operations/maintenance issues, and current site 

conditions. From that base, a team can articulate a set of objectives 

for the site and the diversion upgrade in collaboration with the water 

user. The objectives will deal with multiple resource and operations and 

maintenance issues, which may conflict. The site survey and information 

on site constraints will help the team identify realistically implementable 

alternatives and recommend an optimal alternative. Alternatives often 

include moving the point of diversion, consolidating points of diversion 

to reduce maintenance, and improving water-use technology to reduce 

water demand. 

Any in-channel work requires background information about the 

watershed, the history of the site, and the resources affected or at risk. 

Examples of this type of information are described by the Forest Service 

Stream-Simulation Working Group (FSSSWG 2008, chapter 4), and it is 

embedded in the preparation for stream restoration projects described 

in “Stream Corridor Restoration” (Federal Interagency Stream Corridor 

Working Group 2003). Some of the questions this work can answer 

include:

1. What are the social and natural resource values at or affected by 

the site? Values might include threatened and endangered aquatic 

species, critical aquatic habitats, other water supply infrastructure 

and cultural resources, nearby infrastructure, homes, and so forth. 

2. What is the general geology and soil type (especially the soil 

texture—sandy, silty, clayey, rocky) in the area of the diversion? 

3. What is the hydrologic regime (amount and timing of high and low 

flows, diversion flows)?

4. How frequently does the stream overflow onto its flood plain. If it 

does, risks, such as inundating the ditch headworks and eroding fill 

around the headgate, may become design considerations.

2.1 Step 1: Background Information
17

Chapter 2—Site Assessment and Objectives

5. Does the stream transport large amounts of bed material that can 

deposit upstream of a dam?

6. What are the watershed-scale risk factors, if any? Risk factors 

might be such things as: 

a. A large portion of the watershed was recently burned, or is at 

risk of burning. 

b. The stream was destabilized by a large flood event and is still 

recovering.

c. Road development is increasing the tendency for flooding during summer thunderstorms. 

d. The stream channel is actively downcutting downstream of 

the diversion, and the zone of active erosion is moving upstream.

7. What natural or manmade fish movement barriers exist, particularly in streams with migratory fish? 

Other useful background information for diversion planning includes:

1. What can you find out about the diversion’s management history? 

Agency records might show chronic ditch breakouts, permitting 

issues, changes in ownership, complaints about flooding caused 

by a temporary dam being left in place during high flow season, 

and so forth. The National Forest System Water Rights and Uses 

database should contain administrative data about the site and 

also may include some historical condition information.

2. What is the amount and timing of the diversion’s water use, and 

who owns the right? 

3. Are there land ownership issues? Land ownership may be complex and/or property markers may be absent or imprecise near the 

point of diversion. Many diversions are near national forest boundaries, and confidently determining land ownership may require a 

survey.

4. What other diversions and water rights exist upstream and downstream? How do they relate to each other (including land ownership) and to conditions within the drainage and adjacent drainages? Understanding the big picture of water use in the drainage is 
18

Planning and Layout of Small-Stream Diversions

crucial to planning effective improvements. For example, different 

points of diversion serving the same areas may be an opportunity 

for consolidation. Improved efficiency at one diversion may not improve aquatic habitat conditions if downstream junior water-rights 

holders increase their use.

5. How does the available water supply relate to irrigation or other 

water uses?

Keep in mind that streams may gain flow in some reaches (from natural 

sources or irrigation returns, and so forth) and lose flow in other reaches. 

A simple accounting of mean flow during the diversion season versus 

diverted flow may not present a realistic picture of water availability at 

any one point of diversion.

A reconnaissance walkthrough familiarizes you with the site and allows 

the diverter to explain how (s)he manages it, as well as operations and 

maintenance problems and needs for improvement. Use the opportunity 

to identify and talk over common problems, such as those in table 2.1. 

If the Forest Service Water Rights and Uses Site Visit form has been 

updated recently, this step may have been partly accomplished in the 

course of filling out that form.

Figure 2.1—Where a permanent diversion structure is narrower than the 

bankfull channel, flow accelerating across the structure often scours a plunge 

pool immediately downstream, frequently causing bank erosion and fish 

passage problems. Cottonwood Creek, ID.

2.2 Step 2: Evaluate Existing Conditions and Identify Site Constraints

Words and phrases 

shown in bold are 

defined in the glossary.
19

Chapter 2—Site Assessment and Objectives

EvidenceSilt, sand, and gravel form a bar upstream of the structure. Sediment fills the conveyance ditch. Sediment buries the water control gates or stoplogs. Channel capacity may be low, causing frequent overbank flooding.Reconstruction of pushup dams or any other maintenance of instream structures with heavyequipment can cause an increase in sediment loading. Look for differences in sediment deposition between upstream and downstream reaches. You may find larger or more active bars along the banks or midchannel downstream of the diversion.Sometimes a midchannel gravel bar forms downstream of the diversion structure, causing erosion on one or both banks.Downstream channel bottom is significantly lower than upstream channel bottom, indicating channel incision. Addition of stabilization rock, debris, or several concrete-slab lifts or pours is an indication of maintenance activities to address this issue. Channel bed immediately downstream of check structure may be coarser (i.e., larger rock) than unaffected stream reaches. This can happen when a dam traps fine sediment upstream. By the time the dam pool fills with sediment and sediment begins to move downstream, the downstream reach may have scoured and deepened so much that fine sediment can no longer be retained. Where the diversion structure is narrower than the bankfull channel, or where water falls from an excessive height, a scour hole may have formed downstream (figure 2.1). A headcut or nickpoint downstream that is migrating upstream can destabilize the diversion by lowering streambed elevation and undermining the structure. Evidence of a headcut is a local steepening of channel gradient. Depending on how consolidated or cohesive the bed material is, a headcut may extend over a distance of several channel widths or it may be relatively abrupt. 

ProblemSediment deposition.Increased sediment loading to downstream channel.Lateral channel instability.Erosion/channel incision/headcuts/ streambed scour/bed degradation.

Table 2.1—Common problems observed at diversion structures 
20

Planning and Layout of Small-Stream Diversions

ProblemStream channel dewatered.Elevated water temperature.Lack of riparian vegetation.Accumulation of shrubs, trees, and debris along ditch.Aquatic animal passage upstream and downstream.Debris or sediment accumulation at diversion.

EvidenceThe diversion may remove most of the water from the stream channel, leaving the channel downstream dewatered for miles. Vegetation may be encroaching in the downstream channel. In some cases, substantial dewatering only occurs upstream of a wasteway or fish bypass channel outlet. In this case, layout and/or headgate changes may make it possible to reduce the amount of water diverted above the bypass to maintain habitat and aquatic species passage. Removal of large amounts of water at a diversion can increase the effect of solar exposure and bed heating on the remaining water, so that stream temperature progressively increases downstream of the diversion. Also, backwatering may cause an increase in stream temperature above a dam.Bank disturbance, erosion, high water tables, or dewatering can all weaken bank vegetation. This may contribute to poor security cover for fish, poor forage base (from insect and leaf drop), and elevated water temperatures. Live or dead shrubs, trees, or debris obstructing flows or catching debris in ditch. Trees and deep-rooted shrubs can contribute to leaks or breaks in ditches through holes left when roots die, treethrow, small animal burrows, and ice dams in shaded areas. Diversions can block swimming species passage in both upstream and downstream directions. Upstream passage can be blocked by vertical drops that exceed the jumping ability of the local aquatic species or by streamflow that is too fast or too shallow to swim or crawl through (figure 1.9). Downstream passage can be blocked when the diversion removes all of the water from the stream channel or when aquatic organisms are swept into the ditch without a way to reenter the main channel.Piles of sediment and/or debris in vicinity of a dam.

Table 2.1—Common problems observed at diversion structures (continued)
21

Chapter 2—Site Assessment and Objectives

Table 2.1—Common problems observed at diversion structures (continued)

ProblemInadequate water control.Ditch failures.Fish entrainment in ditch.Operation and maintenance.Vandalism.

EvidenceNo headgate.Headgate not locked.Gullies downslope from ditch overflow.Stream channel diverted down ditch.Poorly controlled diversion structures and headgates often allow excess water to run down the ditch. The ditch may overtop the banks and erode a gully back to the stream channel (figure 3.1). Gullies that start at or below the ditch and repair work to ditch banks are strong indicators that overtopping or piping has occurred or is ongoing.Unscreened diversions are likely to entrain fish. Sometimes, particularly when a diversion is being shut down, fish can be seen congregating just downstream of the headgate unable to reenter the main channel (figure 1.10a).Tarps, hay bales, plastic, and boards left in all year long are evidence of operation and maintenance problems. Spalled or eroded concrete, rotten wood, and corroded or bent metal also are evidence of problems. Discussions with irrigators often reveal ongoing operation and maintenance issues which may require frequent maintenance activities.Inflatable bladder dams have occasionally been slashed. Diversion outlets are plugged by debris and tarps. 
22

Planning and Layout of Small-Stream Diversions

Site Constraints. Almost all diversion structures have constraints 

related to the existing site topography, geology, land ownership, and 

other site infrastructure, among other things. It is important to identify 

where site constraints occur and what limitations they may place 

on improvements to the diversion structure. Site constraints can be 

obvious, such as where bedrock is exposed in the streambed, or they 

may be more subtle. Not uncommonly, a road may run upslope of and 

parallel to the stream, and one or more road drainage culverts may 

directly contribute to the diversion ditch. Runoff from side drainages and 

hillslopes also may be captured by the ditch, possibly delivering water 

and sediment that can damage fish screens and water measurement 

devices, even potentially block or overflow the ditch. Solving this kind of 

problem might involve relocating the fish screen or diversion structure or 

rerouting the road drainage.

Downstream conditions that can constrain diversion upgrades include 

a downstream headcut actively eroding the channel bed or finegrained bed material likely to erode when subjected to water plunging 

over a dam. Another example is an undersized road-crossing culvert 

some distance downstream that backs water up far enough to reach 

the diversion during high flows. Backwatering the site can reduce the 

velocity of water sweeping debris off the screen, plugging the screen 

and reducing the amount of water diverted. 

Potential upstream constraints include important features that cannot 

be inundated by backwater caused by the diversion, such as other 

diversion structures, homes, roads, or vegetation. Table 2.2 lists a 

number of common site constraints.

A basic set of measurements provides enough information to identify 

major issues, establish objectives, develop one or more conceptual 

designs to achieve those objectives, estimate approximate cost, and 

support an application for financial assistance for the upgrade. 

For the survey, establish a temporary but stable benchmark (a location 

that can be relocated and measured from at a later date). Common 

temporary benchmarks include a paint mark on a large rock or diversion 

structure corner, a stake or pin, or a nail in a post or tree.

2.3 Step 3: Survey the Site
23

Chapter 2—Site Assessment and Objectives

Potential Constraint on Diversion Location, Layout, and/or Design

Bedrock is the most obvious site constraint. It is expensive to cut/excavate and 

therefore controls the shape of the structures built on it. Boulder structures are 

challenging to stabilize on bedrock. Sand, silt, and clay also offer engineering 

challenges. Sandy and silty materials are susceptible to erosion and seepage, 

while clayey soils can exert tremendous forces against walls. Ground water 

returning to the surface can cause localized erosion around a diversion 

structure or ditch, destabilizing the structures.

A stream that is well connected to a wide flood plain (e.g., some Rosgen C 

or E channels) may need a diversion structure that tolerates overtopping and 

flooding. A diversion structure in a channel constrained in a steeper canyon 

(Rosgen A or B) may not need to tolerate overtopping, but instream wood 

and large amounts of sediment transported during flood events may influence 

structure selection. 

Gauging stations, bridges, buildings, water control structures, fish screens, 

and ladders all may constrain the footprint of the diversion system.

Land ownership may limit access for construction and/or maintenance. 

Adjacent landowners may not allow moving a diversion structure onto their 

land.

Relocating a ditch or diversion structure may not be feasible where a historic 

structure or site would be disturbed. In addition, certain irrigation supply 

systems have historic importance, which may complicate permitting for 

improvement projects. 

Weak vegetation (overgrazed, weed infested, no trees where needed) affects 

diversion-system design where the area is susceptible to erosion from 

overbank flooding and localized runoff. Such areas need a planting and/or 

vegetation management plan to improve the vegetation’s ability to control 

erosion. 

Protecting habitat and security of threatened and endangered species and 

species of concern sometimes warrants methods that limit site access, timing 

of work, and the diversion footprint.

Table 2.2—Common diversion installation constraints

Condition

Geology/Soils

Stream Type

Structures

Land Ownership

Archaeology

Vegetation

Aquatic and 

Terrestrial Biota
24

Planning and Layout of Small-Stream Diversions

Channel bed and water surface elevations along the channel and ditch 

are key pieces of data for this preliminary survey. When elevations are 

plotted against distance along the channel, the resulting longitudinal 

profile indicates slope, important changes in slope, and the direction 

of waterflow (figure 2.2). The full range of flow conditions—low to 

high—is important to document on the longitudinal profile and on a 

plan view sketch. Use a nearby gauging station if available, a Stream 

Stats estimate for ungauged sites, or enlist the help of the landowner/

diverter to estimate water surface elevations during low and very high 

flows. Look for clues, such as sediment deposited during high flows, or 

changes in vegetation type that might indicate a different frequency of 

inundation. Even if the diversion is not operable during high flows, flood 

elevations are important because the installation must be designed to 

avoid floodwaters entering the diversion ditch. Measuring the elevation 

of the stream bottom and the stream water surface elevation when the 

diversion is operating provides the information needed to calculate the 

control gate size capable of delivering the desired diversion flow. 

In the main channel, the longitudinal profile connects points along the 

thread of deepest flow (the thalweg). If possible, start and end the profile 

at control points downstream and upstream of the diversion. Control 

points are locations where streambed elevation is unlikely to change, 

such as a rock outcropping, culvert, or another diversion structure. 

Channel bed elevation data should be gathered for at least 10 channel 

widths upstream and downstream or 200 feet, whichever is greater. 

Sketch the surveyed section, and annotate survey points.

At various points along the longitudinal profile, measure channel 

widths and elevation of the top of the banks. Measuring low and high 

streambank elevations and channel widths provides information needed 

to calculate wall heights and provide sufficient flow capacity in the 

structure.

Table 2.3 describes what to measure and where, and figure 2.2 identifies 

the survey points in a typical diversion. A site assessment form is 

included in appendix A. 
25

Chapter 2—Site Assessment and Objectives

Table 2.3—Site survey measurements

Notes and Measurements At This LocationIf possible, begin profile at a stable location (control point) where elevation is not expected to change over lifetime of the diversion. Measure the channel bed elevation at the deepest point across the channel (thalweg) and the water surface at that point.For each point, measure distance along the channel length and elevations of the channel bed and water surface. Observe and note bed material sizes and apparent mobility. Are there fresh surfaces on any gravels, cobbles, or boulders? Or are visible surfaces weathered? Is the bed material imbricated?At a cross section where bank height is representative of the reach, note the distance on the longitudinal profile, and measure the top-of-bank elevation on both banks. Also measure channel widths at these cross sections (top-of-bank to top-of-bank).Identify locations where high watermarks are visible on or near the banks. These might be debris lines or high watermarks on a wall, fence, or trees. Describe the high watermarks and measure their elevation. Landowners and water users may be able to offer information about the highest water seen at the site.

Channel LongitudinalStart Main Channel ProfileOther Upstream Points

Measurement LocationProfileAs a rule of thumb, begin longitudinal profile at least 10 channel widths or 200 feet (whichever is greater) upstream of the diversion intake. Ensure this point is upstream of the influence of the diversion. Continue downstream toward diversion, taking measurements wherever there are substantial bed elevation changes or morphological changes within the stream (pools, riffles, runs, etc.). Be sure to measure at fishway entrance, bypass outlet, or other key points related to the installation.
26

Planning and Layout of Small-Stream Diversions

Table 2.3—Site survey measurements (continued)

Notes and Measurements At This Location Measure distance along the channel length, and elevations of the channel bed and water surface. Also, measure the top of bank elevation on both banks as well as the channel width.Measure distance along the channel length, and elevation of the dam crest. For each point, measure distance along the channel length and elevations of the channel bed and water surface. For each point, measure distance along the channel length and elevations of the channel bed and water surface. At a representative cross section, note the distance on the longitudinal profile, and measure the top of bank elevation on both banks as well as the channel width.Measure distance along the channel length and elevations of the channel bed and water surface. If possible, end profile at a stable location (control point) where elevation is not expected to change over lifetime of the diversion. 

Measurement Location Profile Frequently, the channel will be aggraded because of sediment deposition upstream of diversion dam. On a cross section perpendicular to flow and even with the point of diversion, measure at deepest point (thalweg) and shallowest pointCenter of dam.1. Riffle crest or tailout downstream of the plunge pool.2. Deepest part of the plunge pool.Continue downstream from diversion, measuring distance and bed and water surface elevations wherever there are substantial changes.End longitudinal profile at least 10 channel widths or 200 feet (whichever is greater) downstream of the diversion intake. Ensure this point is downstream of the influence of the diversion (plunge pool, fish bypass outlet, etc.).

Channel Longitudinal

Channel Thalweg and Shallowest Point at Ditch/Pipe InletTop of DamPlunge PoolOther Downstream Thalweg PointsEnd Main Channel Profile
27

Chapter 2—Site Assessment and Objectives

Measurement Location Elevation that controls water entering the ditch or pipe.Dimensions of headgate or ditch inlet.100 feet to 200 feet downstream of headgate.

Notes and Measurements At This LocationMeasure pipe or headgate invert or ditch bottom, water surface, and top of bank elevations.Also measure average ditch width (top-of-bank to top-of-bank) about 20 feet downstream of headgate or pipe outlet.Length, height, diameter of headgate.Measure ditch bottom, water surface, and top of bank elevations.Also measure ditch width (top-of-bank to top-of-bank).

Table 2.3—Site survey measurements (continued)

Diversion DitchDitch InletDitch Inlet/HeadgateDitch Slope
28

Planning and Layout of Small-Stream Diversions

Figure 2.2—Example plan and longitudinal profile of existing diversion structure. This plan view shows contour lines from a total-station survey, but a careful sketch indicating survey points and any other important features is all that is needed at the planning stage. Add to the sketch observations of high flow lines, erosion, sedimentation, and so forth. 
29

Chapter 2—Site Assessment and Objectives

While collecting elevation data, consider diversion structure design 

alternatives. Is the ditch steep enough to place a fish screen and/or 

water measurement device? What kind of diversion structure might be 

built that will deliver the water and provide fish passage while limiting 

backwatering, sediment deposition, upstream flooding, and channel 

instability? 

Here is one example of a change that works in some circumstances.

If the channel has degraded (eroded vertically) downstream of the 

diversion, finding another site may be worthwhile. Upstream, the 

stream water surface is higher, so that a lower diversion dam can 

produce the head needed to deliver water to the ditch or pipeline. 

Moving diversions upstream (especially on steeper streams) can 

be an effective method of reducing problems with fish passage and 

erosion by reducing the elevation difference across the diversion 

structure. Often, piping the ditch for some distance downstream of 

the point of diversion allows for a lower diversion structure because 

a pipe has less resistance to flow than an unmaintained ditch, so 

the diversion can function with lower head. Piping also allows you 

to backfill the ditch, which reduces the risk of stream capture by the 

ditch.

There are tradeoffs, however; moving a ditch intake upstream lengthens 

the ditch and the length of dewatered stream channel. Whether the 

tradeoff is worthwhile will depend on how much the ditch would be 

lengthened, how much the stream is dewatered, and how much the new 

location would reduce fish passage or other problems. Land ownership 

also can change along the channel and this may make a move 

infeasible. 

Depending on site conditions and management goals, objectives for the 

diversion installation may include any of the objectives listed on table 

2.4. This is not an exhaustive list; an interdisciplinary team including the 

irrigator should assess the issues and set site-specific objectives. Some 

objectives may conflict with each other, and may need prioritization. 

Examples in table 2.4 include issues and objectives related to the 

stream, aquatic organisms, and operation and maintenance. Operation 

and maintenance issues should and do influence the objectives of 

diversion structure upgrades.

2.4 Step 4: Set Objectives
30

Planning and Layout of Small-Stream Diversions

Notes and Potential UpgradesMany streams in the Western United States are over-appropriated, meaning that the water users have water rights that exceed the amount of flow in the stream during the low-flow season. In some cases, excessive water diversion can be eliminated by providing properly sized, locked, and operable headgates. A simple change in water management, or replacing a ditch with a pipe, may reduce the volume of water diverted.Sediment deposition upstream is caused by slowing the water and reducing the stream power available to transport sediment. Alternatives that might improve sediment transport include replacing the dam with a rock riffle, boulder step, or adjustable weir.If scour is caused by clean water plunging over a permanent dam, add riprap at downstream toe of dam, or remove dam and construct rock riffle or boulder step to permit sediment movement downstream of diversion. Alternatively, a hydraulic engineer may be able to develop a site-specific solution.If downcutting is caused by a headcut that has migrated upstream to the dam, stabilization may require a more thorough analysis of downstream channel stability and more intensive structural stabilization measures.Construct fishway.Replace dam with nature-like rock structure with swimmable pathways and bank edges for crawling species. If using boulder steps, ensure step is not higher than the leaping ability of local aquatic species.

Issue In-Stream FlowSediment DepositionStreambed ScourFish Passage (Upstream)

Potential Objectives Increase in-stream flow downstream of diversion.Reduce degree of dewatering in affected stream reachReduce sediment deposition in the backwater pool by providing for sediment transport through the diversion reach.Limit scour downstream of diversion structure to avoid undercutting the dam.Provide upstream fish passage.Provide upstream passage for local resident and migratory aquatic species.

Table 2.4—Examples of common objectives for diversions
31

Chapter 2—Site Assessment and Objectives

IssueFish Passage (Downstream) and Fish Entrainment in DitchWater QualityWater ControlWater Measurement

Potential ObjectivesProvide downstream fish passage.Reduce water temperature increase.Reduce sediment loading to downstream reaches from earthen (pushup) dam reconstruction/maintenance.Maintain diversion rate with daily or less input from operator.Measure and record volume of water diverted.

Notes and Potential UpgradesFish screens prevent significant numbers of fish from entering the irrigation ditch and being delayed or killed in the ditch system.Limit ponding upstream of the diversion: reduce height of dam or replace with nature-like rock structure.Replant banks for shade if vegetation has been modified.Reduce volume of water diverted. Construct permanent, adjustable dam of nonerodible materials, or replace dam with nature-like rock structure.Control of the water flowing down the ditch can require significant effort from the operator. Too much water down the ditch may breach the banks or flood others with high water. Likewise, it can reduce the amount of water available to downstream water-rights holders.Remote-control or programmable headgates are in use in some water districts. Measurement of water is essential to protecting water resources. Water resource agencies in every Western State have requirements that flows be measured with a “recognized” watermeasurement device. Work with the water user to determine how and where water use should be measured.See chapter 6.

Table 2.4—Examples of common objectives for diversions (continued)
32

Planning and Layout of Small-Stream Diversions

IssueDebris and/or Sediment RemovalFreezing ConditionsDiversion Durability

Potential ObjectivesProvide safe and economical approaches to remove debris and/or sediment.Provide safe and economical approach to operate diversion during freezing conditions.Provide a diversion structure that is flexible and can adjust to dynamic stream conditions.

Notes and Potential UpgradesDebris removal and sediment removal can be a significant impact to the stream and the operator. Sediment removal requires substantial hand labor or moving equipment to the site to excavate and dispose of the excess sediment. In some locales these operations will require permits, causing delays and additional costs. Prevention/reduction of debris accumulation is a high priority. Debris removal can be dangerous; it may require heavy equipment and can be expensive.Alternatives include modifying the diversion to pass sediment and debris. Depending on other objectives, a rock weir or rock ramp may serve this purpose.Some diversions deliver water during the winter to fill reservoirs, deliver stock water, and deliver water to lower elevations, which may have irrigation needs.Avoid installing devices susceptible to freezing or icing. Otherwise, develop an operation and maintenance plan that includes seasonal removal of screens or other portions of the structure that would be damaged by freezing or icing. The diversion structure should be resistant to fire, vandalism, beavers, and the effect of tree roots and other vegetation.Ideally, construct a diversion structure that mimics structures in the natural channel, such as a boulder weir or rock riffle, OR construct a permanent, adjustable dam structure.

Table 2.4—Examples of common objectives for diversions (continued)
33

Chapter 2—Site Assessment and Objectives

IssueFrequency of Required Operation and Maintenance Actions

Potential ObjectivesProvide a stable diversion that requires adjustment as infrequently as possible.

Notes and Potential UpgradesConcrete and steel diversion structures rarely need major adjustment or repair if designed properly. Rock and wood (log/tree) diversions are flexible structures that often need some yearly adjustment to fit the site or prevent leakage. While the diversion structure (dam) itself may need infrequent adjustment, the headgate and any fish protection devices will need adjustment and/or cleaning at a frequency determined by the stream’s water, sediment, and debris regime. Any diversion should be checked for maintenance needs after a storm runoff event. 

Table 2.4—Examples of common objectives for diversions (continued)

35

Chapter 3—Headgates

Headgates control the amount of flow entering diversion ditches or 

pipes conveying water to a downstream use. The headgate type, 

features, and operation also influence the amount of sediment and 

debris entering the ditch. Headgates are generally located at the head 

of the ditch or pipe. Occasionally, a headgate is located some distance 

down-ditch from the point of diversion. In these cases, a wasteway will 

be nearby—a channel or pipe dropping from the ditch in front of the 

headgate down to the main channel to convey any excess water back to 

the main channel.

Headgate-type structures also can be used to measure the volume rate 

of flow being diverted. For this purpose, a weir, flume, or orifice would 

be located downstream of the headgate and any fish screen and bypass 

structures. 

Most headgates on small diversions are hand operated and, during 

periods when main-channel flow is changing rapidly (e.g., spring in the 

northern U.S.), they may need to be adjusted daily. During more stable 

flow periods, however, the gate opening usually remains fixed even if 

flow in the main channel increases, as during a summer storm. Figure 

3.1 shows what can happen to a ditch when it overflows because the 

headgate was not adjusted in time. Larger diversions, such as major 

canals run by water districts, are increasingly moving toward automated 

gates with electronically controlled actuators that open or close the gate 

(see appendix B). The gates may be controlled remotely by an operator 

looking at real-time flow data from a gauge in the main channel. 

Some are programmed to maintain a set water surface elevation (and 

corresponding flow rate) in the ditch, and these respond automatically 

when ditch flow changes.

Chapter 3—Headgates
36

Planning and Layout of Small-Stream Diversions

Figure 3.1—The ditch near the top of this slope overflowed a number of years 

ago and eroded this gully. The eroded material filled the narrow valley bottom 

and rerouted the stream, causing substantial damage to this salmon-bearing 

stream (Moulton 2006). Fourth of July Creek, ID.

Most headgates used at stream diversions are submerged orifice gates 

(figure 3.2a) where the inlet is below the water surface. They usually 

consist of a rectangular or circular plate that slides on rails or pivots 

around a hinge point. An advantage of submerged orifice gates is that 

the through-flow increases slowly with increases in upstream water 

surface elevation. In contrast, at weir gates where water flows over 

the top of a control surface, the amount of water flowing over the weir 

increases rapidly as upstream water surface elevation rises.

3.1 Headgate Types
37

Chapter 3—Headgates

Figure 3.2—(A) Orifice headgate. (B) Weir gate.

Weirs are overflow structures (figure 3.2b) that are used commonly 

as diversion structures in the main channel. They are uncommon as 

headgates, however, because keeping the ditch flow as consistent 

as possible is usually a high priority for operators. For that purpose, 

the submerged orifice is the preferable type of gate. The submerged 

orifice also enables a water-rights holder located downstream of other 

water users to continue diverting even when flow in the main channel is 

extremely low. The location of an orifice gate below the water surface 

(figure 3.2a) increases the likelihood of sediment entering the ditch. If 

sediment is a problem, a weir may be placed in front of the orifice gate to 

limit the amount of sediment entering the orifice. 

Weir gates often are placed at the head of a lateral wasteway to control 

the volume of flow in the ditch. If ditch flow increases over a set water 

surface elevation, water will overflow the weir, and a more constant flow 

is maintained in the ditch. This setup might be used where, for example, 

the ditch is long and receives runoff from hillslopes and small drainages 

along its route (figure 3.3). 

Table 3.1 highlights advantages and disadvantages of weir and orifice 

gates with respect to a number of common problems. Note that detailed 

site designs can mitigate the disadvantages of either type. Weir gates 

are uncommon as diversion headgates.

A B
38

Planning and Layout of Small-Stream Diversions HILLSLOPE AND ROAD RUNOFF DIVERTED INTO DITCH

Figure 3.3—Some ditches receive runoff water from upslope roads and ditches, and some intercept tributary channels. Here, a weir gate maintains a consistent flow in the ditch by allowing overflow into a lateral wasteway that rejoins the tributary a short distance downstream.
39

Chapter 3—Headgates

Table 3.1—Comparing the characteristics of weir and orifice headgates

Water Control

Water 

Measurement

Ditch Capacity

Sediment Intake

Debris Intake

In-Stream Flow

Portability

Orifice Gate

Flow through the orifice gate increases 

slowly with increases in water surface 

elevation. A bypass or secondary gate to 

control flow into the ditch generally is not 

needed.

The orifice gate can be used to 

measure/estimate the flow into the ditch 

with two measurements of water surface 

elevation: upstream and downstream of 

the gate opening.

Fish screen and downstream ditch are 

protected by a mild increase in ditch 

flows with increased stream discharge.

These gates typically entrain a larger 

amount of coarse sediment because 

they remove water from the lower 

portion of the water column where the 

majority of the bedload is transported.

Floating debris does not generally move 

through the orifice. However, when it 

accumulates at the opening, it is not 

easily removed because it is below the 

water surface.

Weir Gate (stoplogs or dam boards)

Flow over the weir gate increases 

rapidly with increases in water 

surface elevation. This requires a 

bypass or wasteway and potentially 

a downstream orifice in the ditch to 

control flow into the ditch.

The weir gate can be used to 

measure/estimate the flow into the 

ditch with one upstream measurement 

of water surface elevation.

Fish screen and downstream ditch 

are at risk because of large increases 

in ditch flows with increased stream 

discharge.

These gates limit the amount of 

sediment entering the ditch because 

they remove water from the top of the 

water column.

Floating debris catches on the weir 

blade at low flows, but passes over 

the weir easily at moderate and higher 

flows. Debris is easily removed from 

the gate.

Both gates may be constructed to leave a set amount of flow in the stream by 

setting the minimum gate elevation higher than the diversion structure crest or 

overflow.

Virtually all metal or wood gates can be constructed offsite, in multiple pieces if 

necessary, and transported to the site
40

Planning and Layout of Small-Stream Diversions

Cost

Availability

Weir Gate (stoplogs or dam boards) 

Generally, the gate must be bolted 

directly to a wall, which results in a 

higher cost.

Weir gates are readily available 

through gate fabricators. Stoplog 

boards are available at hardware 

stores and lumber yards.

Orifice Gate 

The gate can be bolted directly to a 

diversion intake pipe for a much lower 

cost.

Orifice gates are available off-the-shelf 

very economically up to approximately 

24 inches in diameter (canal gates) 

from manufacturers such as Waterman, 

Fresno, and Golden Harvest.

Table 3.1—Comparing the characteristics of weir and orifice headgates (continued)
41

Chapter 3—Headgates

There are many styles of orifice headgates. Usually, the gates are 

bolted to a smooth vertical wall (concrete or steel, figures 3.4 and 3.5). 

They can be sealed quite adequately with gaskets, caulking, or grout. 

Mounting an orifice headgate on the end of a pipe, however, is the least 

expensive and easiest way to install a headgate (figure 3.6). In smaller 

sizes, commercial orifice headgates are relatively inexpensive. Several 

manufacturers make durable cast iron gates that bolt onto pipes or walls 

in standard pipe sizes.

Figure 3.4—Measuring the height of water above the invert of an orifice gate on 

North Brush Creek, Medicine Bow National Forest, WY. 

Figure 3.5—

Modular headgate 

on Fourth of July 

Creek, Salmon 

River watershed, 

ID.
42

Planning and Layout of Small-Stream Diversions

Figure 3.6—Headgate mounted on pipe with concrete headwall and wingwalls, 

Rock Creek, Bear Lake watershed, WY. A fish screen is in the background. 

Sometimes the headgate plate is moved manually and held in place 

with a chain, but generally the mechanism that moves the plate holds 

it in position and controls the amount of flow going through or over the 

headgate. Most headgates are operated using a coarse-threaded (acme) 

rod and a cast iron hand wheel (figure 3.6). However, some water users 

fabricate their own gates from material on hand (plate steel) with little or 

no out-of-pocket cost. The lifting mechanism is often a horizontal pipe 

wrapped with chain or cable. When the pipe is turned by hand (with a 

handle) the cable or chain wraps around the cylinder, shortening and 

raising the gate (figure 3.7). 

Another type of locally fabricated headgate uses wood instead of metal. 

Wooden boards (stoplogs) are cut to fit down into vertical slots. Stoplogs 

are very inexpensive and can function as a weir (water over the top) or 

an orifice (water from below the surface). Adjustments can be as small 

as 1-inch increments. Stoplogs larger than 3 by 8 inches, or longer than 

4 feet, can be very difficult to remove, and constitute an operational 

problem. Usually, spans larger than 4 feet require 3- to 4-inch-thick 

stoplogs.
43

Chapter 3—Headgates

Figure 3.7—Hand-operated windlass headgate, Baker Valley, OR. 

Figure 3.8—Stoplog weir headgate on Soldier Creek, Medicine Bow National 

Forest, North Platte watershed, WY. The plastic sheeting indicates the problem 

occurring with leakage through and under the closed headgate. To the right is a 

rock weir check structure. 
44

Planning and Layout of Small-Stream Diversions

Radial gates are discussed in the next chapter. They can be used 

as headgates as seen in figure 1.10a, as diversion gates in the main 

channel, and even as water measurement structures. We mention them 

here to warn readers about their potential harm to fish, especially when 

used as a diversion gate. In figure 1.10a, you can see the metal bars 

across the back of the gate. If fish are trying to move upstream, they 

may try to jump the barrier. Frequently, they land on these bars and die. 

Head loss across a gate in an open ditch is the difference between the 

water surface elevations upstream and downstream of the headgate. 

Designers attempt to limit head loss across the gate in order to leave as 

much head as possible for any fish screen and to convey water down 

the ditch to the user. They also limit velocity across the gate to limit 

sediment and debris from entering the ditch. These objectives control 

the size of the headgate. In general, sizing the headgate for a velocity of 

approximately 3 to 5 feet per second will provide a conservative (large) 

estimate of headgate size that is adequate for preliminary planning. 

Table 3.2 provides estimates of headgate size for various flows. The 

actual size of the headgate will be determined by the engineer who 

designs the final system or upgrade. 

Table 3.2—Flow and velocity through round and rectangular orifice gates of 

various sizes

 Water Depth 

Measured 

 From The 

Bottom Of 

The Orifice 

Round Rectangular Headgate 

Headgate Headgate Opening Flow Velocity

Height/ Cubic Feet

Diameter width Depth feet per

(inches) (inches) (inches) per second second

8 4 by 12 17 1.7 5.0

12 9 by 12 13 2.9 3.7

15 8 by 24 24 6.9 5.6

18 12 by 24 27 10.4 5.9

24 12 by 36 33 20.0 6.4

3.2 Headgate Sizing
45

Chapter 4—Diversion Structures

Gravity-flow diversions usually require an instream structure to elevate 

the water surface in the main channel and allow water to flow into the 

ditch. Normally, we think of the various types of dams or weirs that 

perform this function, but pumps and infiltration galleries also deliver 

water to the ditch and are included here. This chapter describes how 

each of these structures works, the pros and cons of constructing, 

operating, and maintaining them, and compares their effects on the 

aquatic system as well as their relative cost. 

Weirs are engineered structures designed to raise and protect the 

streambed elevation, forcing water over the weir crest and into an 

operating diversion. They can be permanent or adjustable and full span 

(crossing the entire channel width) or partial span. In this section, we 

include engineered rock riffles, which can function as permanent check 

structures in a diversion setting. Dams constructed from streambed 

sediments (pushup dams, section 4.1.1) also function to raise the water 

surface elevation so that water flows into a diversion ditch, but they are 

not engineered for stability and are good candidates for an upgrade. 

Permanent weirs raise 

the minimum water 

surface (see sidebar) 

and force some or 

all of the water in the 

channel to flow over the 

structure throughout the 

year. They are generally 

constructed of:

● Rock riprap. 

● Logs/timbers. 

● Concrete and steel 

(figure 4.1).

Figure 4.1—Permanent 

concrete weir drop 

structure on Fall River, 

tributary of Henry’s Fork 

Snake River, ID. Photo 

courtesy of Henry’s Fork 

Foundation, Ashton, ID.

4.1 Weirs

The minimum water 

surface elevation is the 

lowest point in the crest 

of the weir structure. 

If the water surface is 

above this elevation, the 

stream is flowing. If the 

diversion inlet is lower 

than this elevation, it is 

physically possible for 

the diversion to capture 

all the water in the 

stream. If higher, some 

flow will always remain in 

the stream. 

Chapter 4—Diversion Structures
46

Planning and Layout of Small-Stream Diversions

Adjustable weirs raise the minimum water surface temporarily. The 

operator can manipulate the structure to achieve variable minimum water 

surface elevations. 

Adjustable weirs may be constructed of rock riprap, logs/timbers, or 

concrete and steel with the adjustable portion consisting of:

● Stoplogs placed in slots or stanchions (moveable slots) (figure 4.2).

● Air bladders (large inflatable composite rubber bags). 

● Tilting weir gates (adjustable, hinged panels that tilt up or down to 

adjust the water surface elevation).

● Rising weir gates (adjustable panels that slide up and down to 

adjust the water surface elevation).

Figure 4.2—Adjustable stoplog weir, Pole Creek diversion, Sawtooth National 

Recreation Area, ID. Flashboards control water surface elevation behind dam 

and waterflow to the diversion (left behind wingwall) and fish ladder (right). The 

structure has a concrete pad upstream and brace downstream to avoid sliding 

or overturning.

All weirs have the potential to affect water quality by increasing water 

temperature, because they slow water and create upstream backwater. 

The degree of impact depends on the degree of solar exposure and 

residence time in the pool. 
47

Chapter 4—Diversion Structures

Permanent full-span weirs constitute a point along the stream channel 

where streambed elevation is nonadjustable. This can create problems 

in a dynamic and frequently adjusting stream system, as most channels 

are. Sediment in transport accumulates upstream of the weir; plunging 

flow over the weir or an upstream-migrating headcut can lower the 

channel downstream of the structure (figure 4.3). Most adjustable 

weirs also affect channel dynamics in this way, because they have a 

permanent sill supporting adjustable panels, stoplogs, or gates. The 

effect is usually less than for permanent weirs, though, because during 

high flows, the weir can be lowered to the permanent sill or floor, which 

can be much lower than the crest of a permanent weir (table 4.1). 

Figure 4.3—Very high velocity water running down this concrete apron caused 

substantial local scour where the apron met the stream, and another flatter 

apron was added. Now, the channel has downcut below the second apron. This 

site is also affected by system-wide channel incision, which has been stopped 

by the diversion structure. Lower Cub River diversion, Bear Lake watershed, ID. 

Table 4.1 compares characteristics of permanent and adjustable weirs. 

Because adjustable weirs can be manipulated as conditions change, 

they have the potential to be less risky to water quality, fish passage, and 

channel stability than permanent weirs. However, actual effects depend 

on how timely the adjustments are. In turn, that frequently depends on 

site accessibility and how easy it is to manipulate dam boards or other 

adjustment mechanisms. The water quality effects shown in 
48

Planning and Layout of Small-Stream Diversions

Design ConcernsHeadcut MigrationChannel Stability: Downstream Scour PotentialChannel Stability: Sediment Accumulation

Permanent , Nonadjustable Weirs (including boulder weirs)Can cause downstream scour because of the plunging flow over the crest during high flows. This is magnified if the structure constricts flow width. Scour can be controlled by good design, such as aprons or embedded foundation rocks. Note that aprons often are barriers to fish movement.Extent of sediment deposition upstream depends on height of weir and design. Sediment accumulation may stress the banks, and could cause erosion if the stream channel tends to shift laterally. Risk of outflanking is greater than for adjustable weirs. 

Engineered Rock RifflesCan be designed to limit local scour and stop headcuts using large (sometimes very large) foundation rocks embedded in well-sorted interlocking rock matrix.Similar to permanent weirs. Flattens upstream channel gradient like a permanent weir and retains coarse bedload material similarly. Fine sediments are likely to pass through the more permeable rock riffle.

Adjustable WeirsHave less potential for downstream scour IF minimum water surface elevation is lowered during high flows.Generally experience fewer problems with sediment accumulation because less backwatering occurs during high flow (assuming structure is adjusted to lower minimum water surface elevation during high flows).

Permanent weirs and adjustable weirs with permanent sills can prevent headcuts from migrating upstream past the diversion, thereby protecting any valuable habitat and/or structures from stream channel incision. Structures may require several steps/weirs to provide upstream aquatic organism passage.

the table vary depending on how easy the weir is for operators to adjust. Likewise, effects on fish passage outside the diversion season also depend on whether the water level controls are actually removed after diversion ends. 

Table 4.1—Comparison of environmental effects and other characteristics of permanent and adjustable weirs and engineered rock riffles 
49

Chapter 4—Diversion Structures

Design ConcernsWater Quality: Temperature and SedimentIncrease in Riparian Ground Water Levels Upstream of the WeirIncrease in Flood Potential Upstream of Weir

Permanent , Nonadjustable Weirs (including boulder weirs) Temperature increase due to pooling upstream of diversion structure depends on solar exposure and flow velocity through the pool. Risk of introducing or mobilizing sediment is less than for adjustable weirs as long as the weir is not outflanked.Are higher and longer lasting. Effects on plant and animal communities can be beneficial or detrimental depending on species, and on wetland objectives at the site.Where the diversion is located on a frequently overtopped flood plain, the extent and duration of flooding is likely to increase more than if the weir were adjustable. 

Adjustable Weirs Have potential for lower or less frequent temperature increases because pool size is adjustable. When check height is lowered, sediment may be mobilized suddenly, releasing a sediment wave downstream.Have lower and shorter duration than for permanent weirs because minimum water surface elevation over the weir can be lowered during high flows.Have less risk of increased flooding during high flows IF gate elevation is adjusted, lowering water surface elevation.

Engineered Rock Riffles Similar to permanent weirs.Similar to permanent weirs.Similar to permanent weirs.

Table 4.1—Comparison of environmental effects and other characteristics of permanent and adjustable weirs and engineered rock riffles (continued)
50

Planning and Layout of Small-Stream Diversions

Design ConcernsUpstream Aquatic Organism PassagePreferential Delivery of Irrigation Flow or An Agreed Upon Minimum Instream FlowRemote or Hard-toAccess Locations

Permanent , Nonadjustable Weirs (including boulder weirs) Can be hydraulically designed to provide aquatic organism passage at some flows, or to serve as a barrier over a range of flows without operator interventionThe minimum water surface elevation (top of weir structure) can be set permanently.May be preferable since no power or operator manipulation is required. Generally require less maintenance.

Adjustable Weirs Compared to nonadjustable weirs, may provide a better opportunity for aquatic species passage outside the diversion season IF dam elevation is lowered to minimum. Can be adjusted to provide aquatic organism passage or to serve as a barrier depending on flow and season. It is easier to provide passage over a wide range of flows with an adjustable check structure.The minimum water surface (top of weir structure) can be manipulated according to irrigation needs and permit agreements.Some systems require power for air compressors, hydraulic pumps, and other machines to adjust the height of the panels.

Engineered Rock Riffles Likely to pass a wider range of aquatic organisms than weirs, but depends on how closely they mimic natural structures in local channel.Same as permanent weirs.Same as permanent weirs.

Table 4.1—Comparison of environmental effects and other characteristics of permanent and adjustable weirs and engineered rock riffles (continued)
51

Chapter 4—Diversion Structures

Design ConcernsOperator EffortCommon Structure Failure Mechanisms

Permanent , Nonadjustable Weirs (including boulder weirs) Annual inspections and any maintenance needed after high flow.Poor design or construction can leave structure vulnerable to:

• Undercutting (caused by a 

headcut moving upstream, seepage under the structure, or local scour). 

• Lateral erosion or outflanking 

(the banks erode upstream and/or downstream and the stream flows around the structure, figure 4.5).

• Erosion or decomposition of 

weir material. Rock riprap may erode from the structure and wood may rot or erode over time. Even high quality concrete may be eroded by bed material abrasion.

Adjustable Weirs In addition to annual and high flow inspections and maintenance, operator must adjust weir elevations as flows change unless the system is automated. Stoplog systems can require strenuous physical efforts to install and remove stoplogs. In addition, emergency stoplog removal can be dangerous (at high flows and icing conditions).Poor design or construction can leave structure vulnerable to same mechanisms listed for permanent weirs. Also, mechanical problems, such as:

• Air bladder damage from 

vandals and/or beavers.

• Panel hinge damage from 

sediment deposition.

• Leaks in air/hydraulic lines due 

to inadequate installation and testing.

• Electronic control failure.• Operator error.

Engineered Rock Riffles Same as permanent weirs.Poor design or construction can leave structure vulnerable to same mechanisms listed for permanent weirs. Some common problems are:

• Rocks too small or poorly 

bedded.

• Foundation rocks not 

properly sized, placed, and/or embedded in a well-graded interlocking matrix. 

• Bank rocks not extended 

high enough or far enough back into banks

Table 4.1—Comparison of environmental effects and other characteristics of permanent and adjustable weirs and engineered rock riffles (continued)
52

Planning and Layout of Small-Stream Diversions

In streams that transport large amounts of sediment, such as many 

channels in the desert Southwest, sediment accumulation can rapidly 

make weirs nonfunctional by filling the pool upstream. Sediment sluice 

gates can be built into the structure to deal with this problem (figure 

4.4). Sudden releases of sediment through the structure during low 

flow can harm downstream aquatic habitat by burying gravels and 

macroinvertebrates. 

Full-span weirs obstruct upstream passage for nonjumping aquatic 

organisms until and unless the crest (or floor slab in the case of 

adjustable weirs) is submerged in high flows so that water no longer 

plunges over it. Even then, many weirs remain upstream passage 

barriers due to high velocities and turbulence. Downstream movement, 

which is often passive, is impeded when fish and other organisms 

are entrained in diversion ditches or when they fall over the crest of 

a structure to land on a hard apron below (figure 4.1). To reduce the 

effects on aquatic species, check structures themselves can often be 

designed to be passable or fish ladders can be constructed around 

them. Fish screens can be placed on ditches. Refer to chapter 5: Fish 

Protection at Diversions.
53

Chapter 4—Diversion Structures

Figure 4.4—Natural Resources Conservation Service design drawing for the San Francisco de Pauda diversion dam, Taos Soil and Water Conservation District, 2005. This diversion site had chronic problems with sediment filling in behind the dam so that water could not be diverted. To fix that problem, the sluice pipe is set 1-foot lower in elevation than the ditch intake, to sluice sediment from above to below the dam. 
54

Planning and Layout of Small-Stream Diversions

Common structure failure mechanisms are listed in table 4.1. Good 

structure selection and design can prevent many of these problems. 

For example, many adjustable weir failures are caused by mechanical 

problems, often due to lack of maintenance or operator error. These 

failures can be avoided or limited by selecting and designing a system 

that conforms to the operator’s ability and willingness to maintain it. In 

addition, using products from proven manufacturers helps avoid these 

problems.

Many structure failures are caused by interactions between the structure 

and the channel (figure 4.5). Understanding channel processes and 

designing for them can help avoid many problems. For example, a good 

design will specify floodwater elevations and flow paths to ensure that 

overbank floodwaters will safely flow around the structure and drop back 

into the channel in designated areas. Downstream activities, such as 

gravel mining, channel straightening or diking, can cause headcutting 

that may affect structures as a nickpoint moves upstream. Protecting the 

banks and the channel with riprap, vegetation, and other measures helps 

to prevent or treat these problems. 

Figure 4.5—Nonadjustable log weir on Fourth of July Creek, Sawtooth National 

Recreation Area. This watershed burned after the diversion structures were 

installed. Note that high flows have already begun to outflank the structure. 
55

Chapter 4—Diversion Structures

Properly designed weirs typically do not experience structural failures, 

such as overturning or sliding. Proper design includes keying the 

structure into the bed with deep cutoff walls to prevent undermining or 

overturning. Massive slabs are used where needed to prevent sliding. All 

weirs need to be keyed into the bank, and most require bank hardening 

(riprap, wingwalls) to avoid outflanking. 

All weirs are subject to a variety of hazards, such as beaver activity, 

vandalism, ice, and channel erosion and outflanking during high flows. 

Like all instream structures, they require inspection and maintenance 

periodically to check for and remove debris accumulations that otherwise 

would reduce functioning and/or stability. Routine monitoring and 

maintenance also ensure that the structure does not fail due to material 

decomposition or erosion.

4.1.1 Types of check structures 

Following is a gallery of weir types, with some explanation about their 

utility and problems. See table 4.2 at the end of this chapter, which gives 

some of the flow and other environmental variables that control their 

applicability. 

Permanent weirs:

Rock weirs.

Rock riffles. 

Rock vanes or barbs (partial span).

Log weirs.

Concrete/steel weirs.

Adjustable weirs:

Stoplog weirs.

Air-bladder weirs.

Adjustable weir gates.

Push-up dams, nonengineered dams.

Streambed intake structures (not a check structure) 
56

Planning and Layout of Small-Stream Diversions

What are they? A channel-spanning structure constructed of rock sized 

to be immobile in the design flow (usually gradations include up to 12-

inch to 48-inch or larger rock) (figure 4.6). Rock weirs used in diversion 

applications are intended to be permanent, and the largest rocks may be 

larger than in the natural channel. Rocks may also be more angular than 

the natural streambed sediments. As far as possible, weirs should be 

designed as passable for local aquatic species.

Figure 4.6—Rock weir diversion structure on Donner and Blitzen Creek, OR. 

Note the low-flow notch in the center that concentrates flows and allows fish 

passage.

Rock weirs often are constructed in a downstream widening arch to help 

keep overtopping flows from eroding the downstream banks. In cross 

section, the structure slopes toward the center of the channel. The low 

crest in the center concentrates low flows, permits fish passage, and 

constitutes the minimum water surface elevation for diverting flow into a 

gravity-fed ditch. Design parameters (rock size, minimum weir elevation 

relative to bank height, bank protection, and so forth) are determined 

considering depth and velocity of the design flow (for diversions, often 

the 25-year flow). Weirs should be spaced at least one bankfull width 

apart to allow for energy dissipation between them. Weir slopes in the 

upstream and downstream directions are typically 5H:1V (20 percent) or 

steeper. 

ROCK WEIRS
57

Chapter 4—Diversion Structures

Rock weirs also can be designed to mimic natural boulder steps (figure 

4.7a) or as cross vanes (figure 4.7b). Detailed design information for 

rock weirs and cross vanes is available from the NRCS (2001), NRCS 

(2008), California Department of Fish and Game (2008), and Rosgen 

(2001), among others.

Figure 4.7—(A) Constructed rock steps raise the water surface to 

headgate elevation at Three Forks Ranch on the Little Snake River, ID. 

(B) Cross-vane diversion structure, Wigwam Fishing Club, South Fork 

Platte River, CO.

B

A
58

Planning and Layout of Small-Stream Diversions

Where are they generally used? Step-pool and pool-riffle channels. The stream should be moderately 

well confined—enough that adding weirs does not increase overbank flood frequency beyond a 

tolerable point. Sites with at least moderate bank stability are ideal; noncohesive (sandy, silty) soils 

require a filter between the weir rocks and the much finer soil to avoid piping and bank erosion. 

Generally, the filter is a layer of gravel or geotextile filter fabric. 

Considerations. Some rock weirs are nonporous, but most are porous, raising the minimum water 

surface elevation while allowing some flow between the rocks. One of the risks associated with 

porous rock weirs is that because of the leakage, minimum water surface elevation may be lower than 

intended, so that less water flows into the diversion ditch. Another risk is that water flowing around or 

under the structure may cause piping or erosion of the soils in which the weir rocks are embedded. 

If severe, this process can lead to structural instability and failure, which can cause fish passage, 

sedimentation, and water delivery problems.

Pros

Rock structures are more likely to permit aquatic 

species passage than smoother concrete or metal 

structures because the rougher rock surface may 

provide some slower flow pathways near the 

banks or between rocks. The height of a rock weir 

can be limited to the jump height achievable by a 

target fish. In steeper channels, one or a series of 

rock weirs can be designed to mimic the structure 

and height of rock steps in the natural channel 

so that aquatic species are likely able to move 

upstream through them.

Water leaking through the rocks may permit 

smaller organisms to swim or crawl between 

rocks.

Bank vegetation can grow in and between the 

rocks, and help stabilize the structure. It may also 

help to moderate water temperature.

Inexpensive if rock is locally available.

Cons

Nonadjustable: Like any structure that raises 

streambed elevation permanently, may cause 

streamflow to overtop the banks at lower flows 

(i.e., more frequently) than normal. Consequences 

might include increased bank erosion, flooding the 

diversion works, eroding the ditch

Water leaking between the rocks can reduce 

efficiency of the diversion and the amount of water 

available for any fish screen and bypass. This 

problem can be managed by sealing the structure 

and maintaining it regularly (see Installation). 

Leakage also can deter larger fish from swimming 

upstream if water depth over the weir crest is low.

Rocks may shift during high flows, requiring 

maintenance.

Structure pools water upstream, which can 

increase its temperature. This disadvantage is true 

to varying degrees for all structures that impound 

water.
59

Chapter 4—Diversion Structures

Installation. Installation cost depends on the availability of rock and 

ease of access to the site. Sealing leaks between the rocks can be 

challenging; plastic membranes, geotextiles, and mixtures of smaller 

gravel and fines are used. Sealing leaks can be important for routing 

enough flow to the diversion, especially if water is being provided for a 

fish screen/bypass system. Rock weirs can be constructed by hand and 

with winches if materials are onsite or can be hauled in with all-terrain 

vehicles (ATVs). 

Streambank and streambed erosion risks can be reduced by keying rock 

weirs deeply into the bed and banks. Bank keys should extend well into 

the banks and to an elevation above bankfull to avoid outflanking. Also, 

footer rocks must be sized properly and placed deep enough to prevent 

weir-crest rocks from rolling into downstream scour holes. 

Operation and Maintenance. Annual inspections are needed to 

ensure continued structure stability and to avoid bank erosion and other 

problems due to occasional rock shifting or rolling during high flows or 

ice events. Replacing boulders that have moved, sealing leaks that have 

opened, and/or removing accumulated debris may all require heavy 

equipment. 

What are they? A permanent channel-spanning structure constructed 

of rock that is sized to be immobile in the design flow (usually 12-inch 

to 48-inch or larger rock). The rock is placed as a sloping blanket along 

the length and width of the streambed downstream of the point of 

diversion, with the goal of raising the water surface elevation at the point 

of diversion (figure 4.8). A series of engineered riffles is often needed to 

raise the water surface sufficiently. 

Engineered riffles are not identical to natural riffles; rock sizes are larger 

for stability, pathways for organism passage may be less diverse or 

different in character, and turbulence may be higher. The crest may 

include larger rocks than average, to ensure it retains its elevation and 

the riffle does not move. Slopes in the downstream direction are typically 

20:1 or 5 percent. The riffle cross section has a low point (thalweg) to 

concentrate low flows for fish passage, and rock should extend up the 

bank to at least bankfull elevation. Engineered riffles are sometimes 

placed in channels without natural riffles. Aquatic species passage 

should not be taken for granted.

ENGINEERED ROCK 

RIFFLES
60

Planning and Layout of Small-Stream Diversions

Figure 4.8—(A) Constructed rock riffles on Upper Rock Creek, Bear Lake 

watershed, WY. (B) Rock ramp—essentially the same as a rock riffle—

constructed in 2007 on the Salmon River, ID.

B

A
61

Chapter 4—Diversion Structures

Where are they generally used? Pool-riffle streams where water surface elevation does not have to 

be raised very much to force water into the diversion. Ideally, the riffle fits into the stream’s pool-riffle 

spacing; that is, it might simply raise and stabilize an existing riffle. A rock riffle might be considered a 

desirable control structure in channels with low banks and channel slopes up to about 4 percent. See 

USDA, NRCS 2007b for an example design. 

Installation. Like all rock check structures, installation cost depends on the availability of rock and 

ease of access to the site. Sealing leaks between the rocks can be challenging; plastic membranes 

and geotextiles have been used, but with time they tend to become exposed and break down. Most 

installations now use only well-sorted mixtures of smaller gravel and fines. Sealing leaks can be 

important for routing enough flow to the diversion, especially if water is being provided for a fish 

screen/bypass system. Rock riffles can be constructed by hand and with winches if rock is onsite or 

rock can be hauled in with ATVs. 

Pros

Depending on the degree of similarity to natural 

streambed structures in the channel, may pass a 

variety of endemic aquatic organisms. Like rock 

weirs, engineered riffles can be designed (using 

hydraulic methods) to pass a target fish within a 

certain flow range.

Inexpensive if rock is available locally and the site 

has good access for equipment. With your own 

equipment, a rock riffle on a small stream can 

be built in a couple of hours. Strict precision with 

elevations is not necessary.

Bank vegetation can grow in the rocks, and 

help stabilize the structure. It may also help to 

moderate water temperature.

Water leaking through the rocks may permit 

smaller organisms to swim or crawl between 

rocks.

Cons

Nonadjustable: Like any structure that raises 

streambed elevation permanently, may cause 

streamflow to overtop the banks at lower flows 

(i.e. more frequently) than normal. Consequences 

might include increased bank erosion, flooding the 

diversion works, eroding the ditch.

Water leaking between the rocks can reduce 

efficiency of the diversion and the amount of water 

available for any fish screen and bypass. This 

problem can be managed by sealing the structure 

and maintaining it regularly (see Installation 

below). Leakage also can deter larger fish from 

swimming upstream if water depth over the crest 

is low.
62

Planning and Layout of Small-Stream Diversions

Streambank erosion risks can be reduced by keying rock deeply into 

gravelly, sandy, or silty banks. Bank keys in these materials should 

extend well into the banks and to an elevation above bankfull to avoid 

outflanking. In tough clayey soils that resist erosion, avoid disturbing the 

soil, and protect the banks with rock placed like riprap. Ensure the center 

of the riffle is low to provide a low-flow thalweg for aquatic organism 

passage. 

Streambed erosion—a potential risk at rock weirs—is also a risk at riffles 

even though water does not plunge over the structure. Both types of 

structures must be constructed to effectively dissipate energy and limit 

downstream scour.

Operation and Maintenance. Annual inspections are needed to ensure 

continued structure stability and avoid bank erosion and other problems 

due to occasional rock shifting or rolling during high flows or ice events. 

Replacing rocks that have moved, sealing persistent leaks, and/or 

removing accumulated debris may all require heavy equipment. More 

frequent debris removal from the top of the riffle may be necessary at 

sites where a lot of water is being diverted and the stream is moving 

debris. 

What are they? These rock structures span only part of the channel 

cross section. When used as diversion checks, they raise the water 

surface in the vicinity of the bank where the diversion is located, and 

permit free flow and aquatic species passage across the rest of the 

channel (figure 4.9). They are usually constructed pointing upstream 

at an angle from the bank (USDA, NRCS 2007a) and sloping down 

from the bank. This helps keep water overflowing the barb away from 

the downstream near-bank area, avoiding bank scour. Like other rock 

structures, the rock is sized to be immobile in the design flow (usually 12-

inch to 48-inch or larger rock).

On streams with mild slopes less than 1 percent, vanes generally should 

block no more than one-fourth to one-third of the bankfull channel width. 

On steeper streams, a barb generally needs to extend across the thalweg 

to influence water surface elevation enough that water flows into the 

diversion. Such a structure may block low flow entirely, in which case it 

is functioning as a weir, or it may simply raise minimum water surface 

elevation while allowing some flow between the rocks or around the end 

of the structure. 

ROCK BARBS/VANES
63

Chapter 4—Diversion Structures

Figure 4.9—Rock barbs bracket a diversion channel on the Uncompahgre 

River, south of Montrose, UT. The barbs were placed to protect the headgate 

(not pictured).

Where are they generally used? Barbs are used where the amount 

of water diverted is small compared with instream flow, and a relatively 

small increase in water surface elevation in the bank vicinity is needed 

to supply the ditch. This means they are most useful on mildly sloping 

streams (<~0.5 percent) with relatively high irrigation season flows. They 

are not useful where a diversion takes all or most of the flow. They are 

best used on wider streams where the vane will not deflect water into 

the opposite bank at moderate to high flows. 
64

Planning and Layout of Small-Stream Diversions

Installation. Like all rock structures, installation cost depends on the 

availability of rock and ease of access to the site. Sealing leaks between 

the rocks can be challenging; plastic membranes, geotextiles, and 

mixtures of smaller gravel and fines are used. Sealing leaks can be 

important for routing enough flow to the diversion, especially if water is 

being provided for a fish screen/bypass system. Cross vanes can be 

constructed by hand and with winches if materials are onsite or rock can 

be hauled in with ATVs.

Operation and Maintenance. Annual inspections are needed to ensure 

continued structure stability and avoid bank erosion and other problems 

due to occasional rock shifting or rolling during high flows or ice events. 

Replacing boulders that have moved, sealing leaks that have opened, 

and/or removing accumulated debris may all require heavy equipment. 

Pros

Does not block entire channel 

cross section, and provides 

free upstream aquatic organism 

passage as well as downstream 

sediment and debris movement. 

Bank vegetation can grow in 

the rocks, and help stabilize the 

structure. Angled construction 

helps avoid bank erosion 

downstream.

Cons

Nonadjustable: Like any structure 

that raises streambed elevation 

permanently, may cause 

streamflow to overtop the banks 

at lower flows than normal. This is 

less likely than for rock weirs and 

riffles because the structure spans 

only part of the channel.

Like other rock structures, must be 

keyed into the bed and banks for 

stability. Keying rocks in to bankfull 

elevation requires substantial bank 

disturbance.
65

Chapter 4—Diversion Structures

What are they? One or more logs or timbers spanning the entire stream, 

and long enough to pass bankfull flow (at a minimum) between the 

banks. Logs may be pinned together, or cabled or chained to ballast—a 

large, heavy object buried in the streambed or bank that acts as an 

anchor keeping the logs from floating away. Like rock and concrete 

weirs, log weirs should have a low-flow notch or slope toward the middle 

of the channel. Constructing them in a V-shape in cross section and 

plan view (V pointing upstream) forces water to converge in the channel 

center, and reduces the tendency to accumulate sediment and become 

vulnerable to outflanking. This also reduces the tendency for water to 

eddy around the downstream banks, which could erode them and lead 

to outflanking. Log weirs should be keyed deeply into bed and banks 

to avoid outflanking and undercutting. Typically, two logs are stacked 

to help avoid undercutting as water plunges over the weir crest (figure 

4.10). 

To facilitate upstream fish passage, construct log (like rock) weirs in 

steps no higher than local fish can jump. Permanent weirs should 

generally not be used where local fish species do not jump, because 

they prevent upstream movement until high flows submerge the drop. 

Possible turbulence below the drop may also affect fish passage. 

Crawling aquatic species have to travel around or over the entire weir. 

Figure 4.10—Two log weirs installed as diversion checks on Fourth of July 

Creek, Sawtooth National Recreation Area, ID. This is the same installation 

pictured in figure 4.5. 

PERMANENT LOG 

WEIRS
66

Planning and Layout of Small-Stream Diversions

Installing no fewer than three log weirs in series is advisable to prevent 

scour from undermining the weir or increasing the drop height. The 

reason is that setting weirs precisely to the intended elevation is difficult, 

and some scour can be expected. Scour holes can be especially deep in 

fine-grained materials. To stabilize grade through the diversion reach and 

ensure that each upstream weir is backwatered by the weir downstream, 

set the weir furthest downstream at current streambed elevation. It is 

less expensive to put in several weirs initially than to go back after some 

downcutting has occurred and add additional controls. 

Where are they generally used? Availability and portability generally 

influence the choice of logs or timbers for a diversion dam. A permanent 

log weir might be the structure of choice in a remote area where logs are 

easily available from adjacent uplands. For small streams without road 

access, small logs can be hauled in cost effectively using ATVs. 

Log weirs require banks that are more stable than those where a rock 

or concrete structure might be placed (see table 4.2). Whereas rock can 

adjust (individual rocks roll or shift) when the streambed or bank erodes 

slightly, logs cannot. Also, they are not impermeable like concrete or 

steel, and water flowing between the individual logs or timbers can cause 

piping in poorly consolidated fine-grained soils, possibly undermining the 

structure. Filter fabric can be used to help limit piping, but if the fabric 

tears, soil can erode through the holes.
67

Chapter 4—Diversion Structures

Pros

Logs are often available 

nearby in forested areas. 

Small logs and other 

construction materials are light 

enough to move using ATVs.

Usually inexpensive.

Cons

Nonadjustable: Like any structure 

that raises streambed elevation 

permanently, may cause streamflow to 

overtop the banks at lower flows than 

normal. 

Banks must be high enough to support 

bank keys, and logs must be keyed 

deeply into the banks for stability. 

Streambed excavation is required to 

bury ballast.

Porous. Leaks are a challenge to seal.

Uniform, straight logs may be hard to 

find.

Failure prone if not properly designed 

for the site and carefully constructed.

Installation. Log or timber weirs require design just like any other weir 

type, and they are not trivial to build. Placing the logs so that they are 

lower in the channel center and angled upstream is important, and 

requires care during construction; getting this wrong raises the risk of 

outflanking. Placing two or three layers of geotextile upstream of the 

structure (figure 4.11) is important to avoid undercutting and piping. 

Bank stabilization measures, such as additional stacked logs, log cribs, 

or rock riprap are necessary. Keying in log weirs generally requires less 

bank disturbance than for rock structures because logs are straight 

and narrow relative to most rocks. A notch into the bank the width of an 

excavator bucket is all that is needed to key them in well. The streambed 

is disturbed if ballast is buried to prevent logs from floating away, but the 

extent of disturbance is less than for rock or concrete weirs. Installation 

in flowing water is difficult since the logs float. 

Operation and Maintenance. Inspections are needed after high flows 

to check for bank erosion, accumulated debris, or other problems that 

could endanger structure stability. Log weirs also should be inspected 

annually for bank and bed erosion, seepage and leaks, and the condition 

of mechanical fasteners (pins, clamps, cables, etc.). Plan for some 

maintenance or repair annually. 
68

Planning and Layout of Small-Stream Diversions

Figure 4.11—Plan and section views and details for a permanent log weir. Adapted from Oregon NRCS standard 

AutoCAD drawings. 

DESIGNED 

BY: 

910 MAIN STREET, SUITE 258 DRAWN BY: 

BOISE, IDAHO 83702 

SHEET 

NUMBER: 

CHECKED 

BY: 

OFF:208.342.4214 

FAX:208.342.4216 

U.S. Forest 

Service 

(adapted from 

NRCS-OR Standard 

CADD drawings) 

SHEET TITLE: 

SCALE: NONE ISSUE DATE: 
69

Chapter 4—Diversion Structures

What are they? Concrete and steel weirs are permanent channelspanning structures of concrete wall or steel piles or panels. These are 

the strongest, most durable, and least porous check structures. Unless 

there is a separate fishway, the entire streamflow passes over the crest, 

so the weir should have a low-flow notch and other design features to 

concentrate low flows and provide for upstream fish passage. 

Smooth concrete walls or steel panels accelerate flow velocity and 

increase downstream scour potential. The streambed and banks 

downstream must be protected from high velocity flows by concrete 

aprons, riprap, and/or energy dissipaters, such as boulder clusters on 

the bed. On banks, riprap and vegetative interplantings are generally 

used for erosion control. Note that in figure 4.12, the weir steps are V-ed 

upstream to help direct the flow and avoid bank erosion.

Figure 4.12—Steel weir, Ochoco Creek, Crook County, OR. Note the low-flow 

notches in the center designed to concentrate flows and allow fish passage. The 

structure has multiple low steps to facilitate juvenile fish passage and dissipate 

energy.

Where are they generally used? Concrete structures are solid and 

uniform compared to log or rock structures, so they can be designed 

strong enough to raise water level higher than either log or rock 

structures can. They are used commonly on larger streams, or where 

a diverter has the right to take most or all of the remaining water in 

the stream. In this case, concrete or steel may be preferable from the 

standpoint of upstream fish passage, because seepage through more 

porous materials like rock or logs would reduce the amount of flow 

available for an upstream passage facility and fish screen. 

CONCRETE OR

STEEL WEIRS
70

Planning and Layout of Small-Stream Diversions

Concrete and steel may be more desirable where soils are porous and/

or highly erodible, and where durability is important. Design methods and 

material properties are well defined for these human-made materials, 

and the structure’s final properties are predictable and reliable. They can 

be constructed with cutoff walls and massive aprons to reliably avoid 

sliding, overturning, and undermining.

Installation. These structures tend to be more costly than other options, 

both because of materials costs and mitigating the risks to the stream 

channel and aquatic organisms. Construction requires dewatering 

the worksite, which can be challenging. Large structures require good 

access for concrete mixing trucks. Concrete, steel, or aluminum for very 

small structures (streams narrower than about 10 feet) could be brought 

in on ATVs and the concrete could be mixed onsite. 

Operation and maintenance. These weirs generally require no more 

than periodic checks for debris accumulation and damage from debris 

battering, bank erosion, or downstream scour. As long as repairs are 

made in a timely way, the structures are highly reliable. 

Pros

Strong, solid structures with 

predictable material properties. 

They may be a good choice in 

erodible soil materials. 

Not as porous as rock or log 

weirs, so at very low flows, 

more water is available for fish 

passage. Very low flows can 

be concentrated through a 

notch.

Durable with regular 

maintenance.

Cons

Nonadjustable; stream may change 

location or elevation, and structure 

doesn’t conform.

If fish passage is not designed into the 

structure, fish moving upstream when 

water plunges over the crest will either 

have to jump or a fish ladder will have 

to be provided. Aprons impede fish 

jumping, and fish moving downstream 

may be hurt when they fall onto a solid 

apron.
71

Chapter 4—Diversion Structures

What are they? Short stoplogs (2-foot to 12-foot boards or tubes) are 

placed in slots or stanchions attached to the floor of the weir (figures 

4-13 and 4-2). Installation and removal of the stoplogs adjusts the water 

surface elevation. Incremental change is generally 2 to 6 inches. 

Figure 4.13—Stoplog diversion dam on Elk Creek, Sawtooth National 

Recreation Area, ID. (A) The dam had a central notch for upstream-migrating 

adult salmonid spawners, but passage for adults was not assured and passage 

for juveniles was believed to be nonexistent (Moulton 2010). The diversion is 

in back and to the right of the dam, unseen in this photo. (B) To improve fish 

passage and habitat, the dam was removed in 2009 and replaced by a well.

ADJUSTABLE

STOPLOG WEIRS

B

A
72

Planning and Layout of Small-Stream Diversions

Where are they generally used? Adjustable dams are used where it is 

not possible or desirable to construct a permanent bed-elevation control 

high enough to divert water throughout the diversion season. Adjustable 

dams allow raising the minimum water surface elevation as flows 

decrease over the summer to continue delivering water to the diversion. 

Stoplog dams can be manipulated by hand, so they are used in remote 

locations without power or automation. Their low cost also makes them 

attractive: they can be constructed of readily available—sometimes even 

surplus—materials. However, it can be quite dangerous to manipulate the 

boards during high flows when water pressure holds them in place, and 

often stoplogs are not removed in a timely way. 

Installation. The structure is comprised of bed and bank keys, floor 

slab and walls of concrete or wood, stoplog slots or stanchions, and the 

stoplogs. Construction generally requires dewatering and bed and bank 

excavation. For small installations, materials may be portable using ATVs.

Pros

Water surface elevation does 

not have to be permanently 

raised, and flow during much 

of the year can be nearer 

normal than is possible with 

nonadjustable weirs. See also 

table 4.2.

These are common, easily 

understandable structures. It is 

relatively easy for landowners 

to understand and approve of 

modifications, such as leaving 

out one or two boards for fish 

passage.

Can be constructed with 

readily available—sometimes 

leftover materials—making 

them inexpensive.

Cons

Due to the difficulty of removing 

saturated boards with water pressure 

against them, boards are sometimes 

not removed in the fall. The resulting 

overflow can cause scour and sediment 

deposition during the next flood event, 

creating an additional maintenance 

need.

Notches may not provide adequate 

passage for fish or other aquatic 

species.

When dam boards are finally removed, 

a concentrated wave of sediment 

may be released to settle out on the 

streambed somewhere downstream.
73

Chapter 4—Diversion Structures

Operation and maintenance. Dam boards should be adjusted 

weekly or more frequently when flow is fluctuating. The site must be 

accessible enough for the operator to make adjustments to the weir 

when floods occur. The operator also must be committed to vigilance 

and timely response during a runoff event that could cause damage to 

the structure, channel, or ditch. Failure to remove dam boards before 

high flows can lead to problems with downstream bed scour, bank 

erosion, fish passage, sediment accumulation behind the dam, and ditch 

breaching and consequent gullying (figures 1.8 and 3.1). 

Inspections are needed after high flows to check for bank erosion, 

accumulated debris, or other problems that could endanger structure 

stability. Weirs also should be inspected annually for bank and bed 

erosion, seepage and leaks, and the overall structure condition. Plan for 

some maintenance or repair annually.

What are they? Rubber air bladders are placed on concrete or wood 

floor slabs, and are protected by hinged steel panels that cover the air 

bladder at all flows (figures 4.14 and 4.15). The air bladder is inflated 

using an air compressor, raising the steel panels that control water 

surface elevation. Elevation adjustments can be made in fractions of an 

inch. At large diversions, these systems can be automated to adjust dam 

height as flow in the main river changes. This allows the structure to 

maintain constant flow in the diversion. 

Figure 4.14—Airbladder diversion dam 

on Ochoco Creek, 

OR. A fish ladder is 

located to the left 

of the photo. The 

structure is reinforced 

at the ends with rock 

riprap to limit erosion 

around the concrete 

wingwalls. Longer 

wingwalls than shown 

here would help avoid seepage and outflanking. A concrete apron prevents bed 

scour at the overfall, and could affect downstream-migrating aquatic organisms. 

AIR-BLADDER WEIRS
74

Planning and Layout of Small-Stream Diversions

Figure 4.15—Schematic drawing of adjustable air-bladder weir. 
75

Chapter 4—Diversion Structures

Adjustable dams are used where it is not possible or desirable to 

construct a permanent bed-elevation control high enough to divert 

water throughout the diversion season. Adjustable dams allow you to 

raise the water surface elevation as flows decrease over the summer to 

continue delivering water to the diversion. Air bladders can be inflated 

mechanically directly by the operator onsite or remotely, or they can be 

adjusted automatically. The inflation system requires electrical power at 

the site.

Fine sediment can plug the weir’s hinges so that the panel has difficulty 

opening. Air-bladder weirs are less sensitive to this problem than other 

adjustable or tilting weirs because the bladder exerts pressure over the 

whole panel area, resulting in large forces that can overcome some sand 

embedded in the hinge. Nonetheless, air-bladder weirs would not be the 

first choice of structure type in channels that transport large amounts of 

sand and silt-size sediment. 

Pros

Water surface elevation does 

not have to be permanently 

raised, and flow during much 

of the year can be nearer 

normal than is possible with 

nonadjustable weirs.

Less dangerous than handplaced stoplogs and more 

likely to adjust in a timely 

way, because no manual 

manipulation is needed.

Compared to stoplog weirs, 

more likely to seal tightly, 

allowing more water to be 

sent through a constructed 

fish ladder and/or a fish 

screen/bypass system.

Cons

Grid electricity or a generator and 

engine are required onsite to run the 

air compressor. Solar panels do not 

generate enough power. Power is not 

required all the time—only when water 

surface elevation needs to be changed.

Upstream fish passage requires an 

off-stream facility: a fishway, such as a 

ladder or a side channel.

If construction is not done well, 

experience shows that pipes running 

to the bladder develop small leaks, 

creating the need to run the air 

compressor frequently. 

See also table 4.1, which lists advantages and disadvantages of 

adjustable versus permanent diversion structures.
76

Planning and Layout of Small-Stream Diversions

In areas with active beaver colonies, air bladders are at risk of being 

chewed. Both beavers and human vandals have caused failures 

by puncturing air bladders. A way of reducing their susceptibility to 

punctures is to have ceramic chips or rods mixed in with the rubber 

material during fabrication. 

Installation. The structure is comprised of bed and bank keys, floor 

slab and walls of (usually) concrete, an air bladder, air compressor, and 

a steel panel. Construction generally requires dewatering and bed and 

bank excavation. Precision construction is required to create a level 

surface and allow for sealing the bladder tightly to the walls and floor. 

The plumbing serving the bladder should be installed carefully and 

sealed to avoid leaks developing later.

Operation and maintenance. The operator must conduct startup and 

ongoing maintenance of the air compressor. If the air compressor is 

operating frequently even when the water level is not changing, check 

for leaks in the airlines to the bladder. The weir plate also should be 

checked annually for sediment accumulation at the hinge, and cleaned if 

necessary. Check the bladder for small punctures.

Inspections are needed after high flows to check for bank erosion, 

accumulated debris, or other problems that could endanger structure 

stability. Weirs also should be inspected annually for bank and bed 

erosion, seepage around the outside walls, and overall structure 

condition. Plan for some maintenance or repair annually. 

What are they? This category includes several types of adjustable 

weirs that are seen rarely on national forests, but might occasionally 

be encountered, especially at large diversions. In general, these weirs 

mostly have been replaced by air bladder weirs, which are easier to 

manipulate and more reliable. 

One type of adjustable weir gate slides up and down between vertical 

walls on either side of the channel. It might be on tracks, or simply 

set against concrete walls. Hydraulic or air cylinders, lead screws, or 

winches might move the gate. 

Tilting weirs (figure 4.16) have a panel that is hinged or attached to 

a tube that rotates. The hinge or tube is attached to the floor of the 

structure. The panel is raised or lowered by means of a cable winch or 

torque tube to change the water surface elevation.

ADJUSTABLE WEIR

GATES
77

Chapter 4—Diversion Structures

Figure 4.16—Schematic drawing of tilting weir with concrete sill and wingwalls.
78

Planning and Layout of Small-Stream Diversions

Radial gates (figure 4.17) are curved plates—commonly of corrugated 

galvanized steel—that rotate around a hinge on the weir sidewall, 

and are raised by a cable winch. This type of adjustable gate is 

highly undesirable for fish because when closed or only slightly open, 

upstream-migrating fish may attempt unsuccessfully to jump the gate 

and they may be stranded after landing on the horizontal bars or shelves 

visible in the photo. 

Figure 4.17—Radial gates at lower Cub River diversion, Bear Lake watershed, 

ID. These gates are open now, but when closed, they raise the upstream water 

surface elevation by about 21⁄2 feet. 

Where are they generally used? Adjustable-gate weirs that slide 

vertically are more appropriate for taller check structures where there 

is enough fall across the weir to keep it clear of sediment that would 

prevent the gate from closing. Because they do not take up much 

channel length, they are more likely to be used where the water surface 

elevation must be raised up high. 

Tilting-weir gates are susceptible to hinge damage from fine sediment, 

and they require problematic synchronized lifters on both sides of the 

channel. They are rarely used for these reasons. 

In salmonid habitats, radial gates are used rarely now because of the 

harm they cause to migrating adult fish. 
79

Chapter 4—Diversion Structures

Installation. Because these weirs are set in concrete walls, installation 

issues are similar to those for concrete weirs. They are more complex 

because power must be supplied, and gate actuator mechanisms also 

must be installed unless the gate is hand manipulated.

Operation and maintenance. For vertical sliders and radial weirs, debris 

must be removed from the floor so that the weir can seal. All adjustable 

weir gates require annual startup maintenance, winch maintenance, 

bearing and gear lubrication, and cables checked for fraying. 

Pros

Mechanically adjustable.

Like other weir styles, flow 

over the crest increases 

rapidly with increasing 

upstream head. Therefore, 

these are good for maintaining 

a relatively constant upstream 

water surface elevation and 

ditch flow even when instream 

flow increases greatly. 

Radial gates are wellbalanced and easy to lift. 

They work well with high 

sediment loads because the 

hinges are out of the water. 

Radial gates can be moved 

easily using a hoist setup.

Cons

Poor in streams with high sediment 

loads because sediment resting on weir 

floor can prevent gate from closing. 

Fine sediment can bind hinges of tilting 

weirs.

Radial gates are quite dangerous for 

upstream migrating fish because they 

attract fish and encourage them to 

jump at the back of the gate.
80

Planning and Layout of Small-Stream Diversions

Pushup dams and pole-and-tarp dams are some of the most common 

check structures at farm diversions. Pole-and-tarp dams are hand built 

using whatever materials are handy to raise the water surface elevation 

high enough to run it into the ditch (figures 4.18 and 4.19). Pushup 

diversion dams are constructed by hand or heavy equipment from 

streambed or streamside rock and gravel. Wingdams are one example 

common on the Salmon River and its tributaries (figure 4.20). They are 

quasi-permanent nonengineered barbs that extend at an acute angle 

from the streambank across as much as 75 percent of the channel width. 

These check structures have serious disadvantages. For example, the 

headgate is often some distance down the ditch, and the ditch upstream 

of the headgate can be overtaxed by large volumes of water, especially 

when the stream is running high. Fish are also diverted into the ditches 

supplied by these diversion structures, and fish screens and safe 

bypasses back to the stream are generally not provided.

Figure 4.18—Check structure using logs to support a plastic tarp on the 

Medicine Bow National Forest, WY. The ditch is to the left out of the photo. This 

check structure is not removed at the end of the season. 

NONENGINEERED 

CHECK 

STRUCTURES
81

Chapter 4—Diversion Structures

Figure 4.19—(A ) Pole-and-tarp diversion structure on upper Rock Creek, Bear 

Lake watershed, WY. The diversion is not active in this photo, but tarps and 

sheet metal are visible on the bank. (B) Hand-placed rock check with tarps and 

other materials on Big Casino Creek, Sawtooth National Recreation Area, ID.

B

A
82

Planning and Layout of Small-Stream Diversions

Figure 4.20—Bulldozer-constructed wingdam with diverted water in foreground. 

East Fork Salmon River, ID. This diversion was replaced and combined with 

another diversion in a Bureau of Reclamation project aimed at reducing harm 

to anadromous and resident fish species in 2003. Photo courtesy of Brian 

Hamilton, Bureau of Reclamation, Salmon, ID.

Using a bulldozer or excavator to construct a pushup dam disrupts the 

streambed on at least an annual basis, and if the dam washes out in a 

summer storm, disturbance can be more frequent. Pushup dams often 

are not removed after the diversion season, but are allowed to erode 

during high flows. Water quality effects of dam washouts may or may not 

be important, depending on the system. 

Pushing streambed materials around loosens the streambed and 

mobilizes sediment for transport. The disturbed streambed materials 

are more prone to erosion and the streambed may scour, creating a 

zone of scour that moves upstream and can require the wingdams to be 

extended in a continuing cycle. Direct streambed disturbance may be 

much less of an issue with hand-built pole-and-tarp dams.

Leakage is an operational problem with these dams. It may reduce 

the amount of water diverted, as well as the amount of water available 

to operate a fish screen and bypass fishway. Often, straw or plastic is 

added to pushup dams to seal them. 
83

Chapter 4—Diversion Structures

Pushup dams are being replaced in many locations where water 

conservation, channel stability, and aquatic ecosystem functioning are 

management goals. Figure 4.21 shows the structure that replaced the 

pushup dam in figure 4.20. It is a rock weir with two drops sized to permit 

passage of endemic fish species.

Figure 4.21—Two diversions, including the pushup dam in figure 4.20, were 

consolidated into one on the East Fork Salmon River. The new diversion 

structure is an A-weir with two rock weir drop structures for salmonid fish 

passage. Photo courtesy of Brian Hamilton, Bureau of Reclamation, Salmon, ID. 

What are they? An open pipe or narrow box embedded in the streambed 

with a downstream-sloping grating across the opening for water to enter 

(figure 4.22). Streambed intake structures differ from infiltration galleries 

in that they are open at streambed elevation, whereas pipes feeding 

an infiltration gallery are buried in the streambed. The structure may 

or may not span the entire streambed. Water runs by gravity through a 

valve to the distribution infrastructure—a pump sump, ditch, or pipe. The 

structure slopes toward the bank steeply enough to sweep any coarse 

sediment to a sump that can be cleaned out or to a sediment sluice gate 

if the amount of trapped sediment is high. Perforated-plate or wedge-wire 

fish screens may be secured on top of the grating to protect fish from 

being sucked into the diversion. Screens also help keep gravel out of the 

diversion. 

STREAMBED INTAKE

STRUCTURES
84

Planning and Layout of Small-Stream Diversions

These structures work well only where there is plenty of flow that will not 

be diverted. The gratings tend to take in water so fast that, in shallow 

water, most of the surface flow may enter the top of the opening and 

return back out again at the downstream side of the grating, leaving the 

middle section dry or nearly dry (figure 4.23). Downstream-migrating fish 

may be able to negotiate the narrow dry patch by flopping and rolling 

but when leaves and twigs are allowed to accumulate there, fish may be 

blocked and die. Such structures require diligent maintenance to keep 

them clear of debris. For these reasons, streambed intake structures are 

often frowned upon by regulators.

Figure 4.22—Streambed grated intake structure in Boundary Wildlife 

Management Area, Boundary Creek, ID, operating at low winter flow. This 

structure is operated by hand to maintain instream flows; no water is diverted at 

flows less than 50 cubic feet per second (cfs). Permissible diversion rates vary 

depending on flow in the main channel, and the maximum permissible rate is 20 

cfs. 
85

Chapter 4—Diversion Structures

Figure 4.23—Streambed water intake and fish screen on Clear Creek, near 

Halfway, OR. This structure is a corrugated metal pipe with rectangular holes cut 

in the top that are covered by a grating. The grating slopes downstream 6 inches 

in 2 feet (25 percent) so that flow across the top will sweep it clear of debris. 

This works as long as the grating is submerged, but at low flows, all streamflow 

may enter at the top and resurface near the bottom, creating a problem for 

debris and fish passage. Note the piece of culvert at the far side of the stream 

channel. It acts as a low dam narrowing the channel so that water flows toward 

the diversion structure. An opening for upstream fish passage can be seen 

between the two structures.

A different type of gravity intake structure—an end-of-pipe intake 

screen—can work in limited situations (figure 5.11), where the diversion 

takes only a small fraction of streamflow. This device sits on or slightly 

above the streambed where water is reliably deep enough, perhaps 

in a midstream pool or deep glide. Unlike streambed intake structures 

that are swept by the flow, passive end-of-pipe screens require frequent 

checking to remove debris. To avoid that, many end-of-pipe screens 

include air or water backwash cleaning systems. These screens can 

effectively prevent fish from entering the ditch or conveyance pipe if they 

are designed properly. See section 5.1.3. 
86

Planning and Layout of Small-Stream Diversions

Where are they generally used? Streambed intake structures have 

been tried, but not used extensively in the Pacific and Inland Northwest 

States because of regulatory agency objections to possible ‘take’ of listed 

fish that could occur if the grating is not kept clear of debris. In other 

States, they may be useful at sites where plenty of high-velocity bypass 

flow is available to sweep debris from the screen and/or keep the entire 

structure submerged at all flows. Like all permanent diversion structures, 

they require engineering design and construction supervision. 

Installation. Like other instream structures, streambed intakes require 

instream construction permits, dewatering (critical to the success of 

any instream concrete structure), and accurate elevation control to set 

structure at correct grade.

Operation and maintenance. If the structure is designed properly to 

handle local variability in flow and sediment loading, little operation and 

maintenance attention is needed. If no fish screen is installed, sediments 

smaller than the grating openings are likely to fall in or become wedged 

in the openings. If a fish screen with 3/32-inch openings is installed, 

sand grains stuck in the openings can generally be removed by pressure 

washing or by breaking the grains off with a shovel. 

Pros

Do not block streamflow; do 

not cause water quality or 

channel stability problems 

associated with ponding 

or sediment and wood 

accumulation as upstream 

of a dam, or with streambed 

erosion downstream.

Easy to prevent fish 

entrainment by placing 

approved screen materials on 

top of grating.

Assuming good design and 

installation, requires little effort 

to operate and maintain.

Cons

All surface flow may enter at top of 

grate, leaving midsection dry. Even if 

most flow resurfaces at downstream 

end of grate, downstream-migrating 

fish may come in contact with the 

grating.

If maintenance is needed, it would be 

instream work, possibly requiring a 

permit depending on State law.
87

Chapter 4—Diversion Structures

Pumps are used to raise water to a higher elevation or pressure. They 

can be placed in a pool in the channel, but instream placements are 

vulnerable to sediment and debris accumulations. Whether they are 

placed inchannel or off, pumps nearly always require an intake screen 

to protect aquatic organisms and the pump itself. One of the principal 

considerations for locating pump stations is the need for electric power.

For a permanent pump station, a screen is placed at the bank toe 

(figure 4.24) or on the streambed (figure 4.22). Water entering the 

screen is conveyed by gravity to a sump located adjacent to the bank. 

The bottom of the sump and the pump suction should be located 

several feet below the low water surface elevation to access water at all 

design flows. Installing a permanent, screened pump station requires 

heavy-equipment access to the site, dewatering, and some inchannel 

excavation. 

Figure 4.24—Bank screen protecting pump station located behind bank, 

Kalapuya (also spelled Calapooia) River, near Brownsville, OR.

4.2 PUMP STATIONS

The pump suction is the 

end of the pipe where 

water is drawn into the 

pump.
88

Planning and Layout of Small-Stream Diversions

Pumps and/or generators also can be located on the streambank, 

connected to moveable screens and pipes that are moved as flow in the 

source channel changes (figure 4.25). Such a pump station may have 

almost no permanent impact on the channel itself, and it affords great 

flexibility in operation. However, the operator needs to be extremely 

careful about keeping track of flow changes. Nonfloating equipment may 

need to be moved rapidly to protect it from flooding or being washed 

away. Likewise the pump could burn out if water level drops leaving 

the intake dry. This kind of pump station is appropriate on big, relatively 

flat rivers where there is plenty of water depth and flow is not fast or 

turbulent enough to make the pump and screen gyrate or swing, which 

could disrupt water delivery.

Figure 4.25—Streambank pump with floating screened pump suction on Bear 

River, UT. Photo courtesy of Warren Colyer, Trout Unlimited. 

Advantages

Pumps have several advantages over other types of diversion control 

structures. 

● Water surface elevation in the stream does not have to be raised 

for a pump station intake.

● Temporary or removable pump intakes may be taken out of the 

stream to protect from ice and debris damage.
89

Chapter 4—Diversion Structures

● Total diversion flow is not changed significantly by normal 

variations of instream water depth. (Therefore, diverted flow does 

not change much during storm-runoff periods.)

● Pump suction screens are an off-the-shelf item preapproved for 

use in several Northwest States.

● Pumps can be lowered to follow water as the streamflow 

decreases.

Disadvantages

Pumps also have several disadvantages compared to other types of 

structures. 

● Continuous power requirements (either electricity or fuel).

● Removable pump stations may be hard to reinstall at high flows 

(occasionally spring runoff occurs when crops require significant 

irrigation).

● Pumps require maintenance that the irrigator may not be qualified 

to perform (i.e., motor rewinding, seal replacement).

● Pumps are subject to damage from flooding.

How pump stations fail

Typical failure modes include:

● Mechanical Failure

■ Bearing and shaft wear due to abrasive sediment load (sand).

■ Impeller wear (sand).

■ A hole in the screen can allow debris into the pump causing 

impeller damage.

■ Screen can plug and the pump can burn out.

■ Pump is damaged by cavitation (because pump is placed too 

far above the water surface).

● Stream Mechanics/Site Design Errors

■ Sump fills with sediment.

■ Pump suction location is damaged by streambank erosion.

■ Pump is flooded at high water or pump suction is high and dry 

at low water. 
90

Planning and Layout of Small-Stream Diversions

In mountain rivers transporting sand and silt, pumps frequently fail 

when the pool they are placed in fills with sediment, and the sand wears 

out the pump bearings and impeller. Beware of constructing a weir or 

crossvane in such a stream with the idea of creating a deep enough hole 

for a pump. Sediment deposition is likely to create problems there. 

These failures can be avoided or treated by designing systems tailored 

to site conditions. For example, designers should select a pump and 

screen that can tolerate sand if the stream transports large amounts of 

sand. The screen should be durable, and it should be protected by a 

trash rack or other protective structure if the screen might otherwise be 

subject to damage from debris. The pump location should be protected 

from erosion and flooding. Using pump and screen designs from proven 

manufacturers and vendors will help in avoiding some of these problems. 

Also, designers should try to assure that the pump installation will not 

require more diligent inspection and maintenance than the operator is 

able and willing to supply. 

Figure 4.26 shows how stream adjustment can sabotage a pump 

installation. A log-crib diversion dam, a remnant of which can be seen in 

the foreground, was removed to facilitate fish passage on the Kalapuya 

River in Oregon. A pump station replaced the dam; its screen is visible 

on the left in the process of being cleaned by waterburst. Dam removal 

planners had predicted the main thread of flow in the restored channel 

would be at the outside of this gentle bend, near the screen. However, 

the thalweg is currently located away from the screen, and the screen 

may not receive flow at the driest time of the year. 

Figure 4.26—Kalapuya River pump station and river context. See text for 

explanation.
91

Chapter 4—Diversion Structures

4.2.1 Types of Pumps

In general, the pumps used for diversions are similar in terms of 

function. Centrifugal pumps, propeller pumps, and turbine pumps all 

have an instream screen connected to a sump or pump suction. All can 

be specified to handle debris and sediment. The biggest differences 

are in the packaging: can the pump be submerged? Can the motor be 

submerged? 

Propeller and turbine pumps are similar in having the motor and pump 

impeller coupled via a shaft. These need permanent installations, where 

the motor can be located high above the water out of reach of floods on 

something like a dock or pier (figure 4.27). The propeller pump operates 

only at low pressure; turbine pumps operate at low to high pressures. 

Figure 4.27—Propeller pump installation at Hart Lake, OR.

In centrifugal and submersible pumps (figure 4.28), the motor and pump 

impeller are closely coupled. The centrifugal pump is placed no more 

than about 15 to 20 feet above the water surface, which can limit its use 

on large rivers with very high banks. Submersible pumps are placed 

below the water surface. Both centrifugal and submersible pumps can be 

simple, easy-to-move packages including a pump, a protective screen, a 

water delivery pipe, and a power cord. 
92

Planning and Layout of Small-Stream Diversions

Figure 4.28—Submersible pump on skids to raise it off the streambed. Mounted 

to the pump housing is a fish screen cleaned by a water-backwash system. 

4.2.2 Pump Operation and Maintenance

When the pump and screen are operating properly flow in the diversion is 

very reliable and uniform. However, one of the disadvantages of pumps 

is their need for consistent attention to operation and maintenance. 

Pump and motor maintenance includes replacing seals and/or packing, 

and bearing and shaft replacement. Approximately every 20 years the 

motor will need to be rewound. 

Operation costs are quite inexpensive. Per horsepower-day, electric 

pumps use about $15 to $20 per kilowatt hour and diesel pumps use 

about 1 to 1.5 gallons of diesel fuel.

Stationary pump stations require removing sediment from the screen and 

sump (with backwash, sluicing, suction, or excavation). Moveable pump 

stations require removing the pumps at the end of the irrigation season 

and reinstalling them at the beginning of the next season. Replacement 

of the pumps during high flow can be very challenging.
93

Chapter 4—Diversion Structures

Pumps can catch fire and be damaged by vandals, beavers, and 

other nuisances. They also can be damaged by lightning, low voltage, 

flooding, and overheating. A sunshade can safeguard the installation by 

preventing overheating due to sun exposure. Sunshades can decrease 

operating temperatures 20 °F or more. 

Infiltration galleries are notoriously difficult and expensive to install, 

and they are appropriate only at limited sites. Even at an appropriate 

site, design and construction can be complicated. They are not 

recommended unless the owner is willing to commit significant 

resources, and to undertake diligent maintenance. In the Pacific 

Northwest, the National Marine Fisheries Service considers them 

experimental (NMFS 2008). 

Infiltration galleries consist of a series of perforated pipes or conduits 

installed below the local water table, either directly below the streambed 

or off channel (figure 4.31). Typically, water is conveyed to a pump 

intake or sump. Only sites with poorly-graded coarse subsurface 

materials are suitable for infiltration galleries. Low permeability materials 

that limit the rate of subsurface flow into the pipes are a common cause 

of failure. 

Infiltration galleries are at high risk of clogging in most streams. This is 

true even where the pipes are surrounded by a gravel filter to prevent 

the buildup of fine sediment that can clog the pipes. Commonly, the 

filter is a poorly sorted mix of coarse gravel, open-graded enough that 

fine sediment can move with the flow through the system and into the 

ditch. This kind of filter does pose a risk to fish fry, since some fry may 

be smaller than the largest pores and can also be swept through the 

system. Although some infiltration galleries are equipped with air or 

water backwash systems to clean out the pipes and reset the gravel 

filter, these systems require significant organization and effort to work 

effectively. In addition to plugging by fine sediment, algae and moss 

growth can plug the pipe openings, and greatly increase the risk and 

required size of the infiltration gallery. 

Infiltration galleries that use steel pipe or other materials that are not 

corrosion resistant are particularly susceptible to plugging. Corrosion 

raises blisters (carbuncles or tubercles) on rust-prone surfaces that can 

cause plugging, as can calcium deposits from carbonate-rich water. 

4.3 INFILTRATION GALLERIES
94

Planning and Layout of Small-Stream Diversions

Figure 4.29—Drawing of an infiltration gallery that delivers water to a vault and irrigation pipe. Backflushing 

equipment must have access to the vault to clear each pipe on a regular basis. 
95

Chapter 4—Diversion Structures

Advantages

● Water collected by infiltration galleries is typically of better quality 

than surface water collection as it has been filtered by streambed 

sediments.

● Infiltration galleries are less likely to experience vandalism or theft 

than aboveground systems due to the system being below grade.

● Infiltration galleries do not impact the transport of sediment as 

much as aboveground structures.

● Infiltration galleries present no obstacle to upstream fish passage 

and very few obstacles to downstream fish passage (i.e., no need 

for fish screens).

Disadvantages

● Installation is difficult and expensive; regulators tend to view them 

skeptically because of experience with many failed systems.

● Installation requires disturbing the streambed or riparian area. 

● Effectiveness is highly dependent on site and stream conditions; 

design usually requires a geotechnical investigation. 

● Appropriate sites are limited to poorly graded coarse sediments 

with little fine sediment in transport; may require design modifications during construction to fit site conditions. 

● Infiltration galleries have a history of failing when they are installed 

improperly in low permeability alluvium or in streams with heavy 

fine sediment loads or algae growth. 

● Installation costs tend to be higher and maintenance work is 

generally more difficult due to the system being below grade. 

Maintenance includes backflushing with air or water to remove fine 

sediments and algae. 

● The infiltration gallery system must be carefully designed to avoid 

taking too much water and dropping instream flow levels below acceptable limits.

● Infiltration galleries are best suited for low volume or intermittent 

diversions.
96

Planning and Layout of Small-Stream Diversions

How Infiltration Galleries Fail

Infiltration galleries may fail for several reasons. These include:

● Clogged perforated pipe or surrounding gravels (fine sediment, 

organic materials, algae, corrosion products). 

● Limited permeability of surrounding alluvium. 

● Eroded streambed exposes infiltration gallery.

4.3.1	 Infiltration gallery operation and maintenance

Maintenance costs can be very high for poorly located, designed, or 

installed infiltration galleries. Sediment removal and pipe replacement 

are the primary maintenance costs. 

Assuming the site is suitable for an infiltration gallery, a well designed 

and constructed installation may operate for years without any significant 

excavation and repair. However, periodic (usually at least annual) 

backflushing with air or water is required to remove fine sediment 

buildup, and these backflushing operations tend to be quite large and 

relatively expensive ventures. The frequency of sediment removal varies 

considerably, depending on site soils and the quantity of fine sediment 

present. 

Daily operating costs for infiltration galleries that are properly located 

and designed are relatively low. Once installed, the infiltration gallery 

should function without operator input or intense supervision. The main 

operating cost for the system would be in the pump operation.

Some adjustable weirs and all pumps use lubricants, fluids, and fuels 

for operation and to provide backup power. Head gate lead screws, 

chains, gear boxes, bearings, and operators also use them, as do the 

moving parts of fish screens. Batteries also may be part of a diversion 

installation. To protect the stream and riparian area, diesel or gasolinepowered installations should have containment structures around fuel 

tanks, fuel lines, and engines. Oil-lubricated pumps (propeller and 

turbine) should use oils approved for use in and around streams (or 

food) by the U. S. Environmental Protection Agency. Oils also must be 

approved for use by the pump manufacturer.

4.4 Toxic Materials
97

Chapter 4—Diversion Structures

In virtually all installations, some of the materials used may be toxic to 

aquatic organisms prior to curing or hardening (uncured/soft concrete, 

uncured epoxy paint, resins). During installation, water should be kept 

away from these materials until they harden. They are safe for aquatic 

organisms after hardening. If pressure treated wood might be used for an 

upgrade, investigate whether its use in water bodies is regulated in your 

area or State. It is toxic to aquatic organisms prior to curing. 

Diversions do not contribute to water pollution so long as adequate care 

is taken to prevent water from contacting petroleum products, batteries, 

and toxic materials prior to curing. 

Table 4.2 indicates the appropriate range of channel and flow 

characteristics for each type of structure. The numerical ranges are 

based on several assumptions:

● The design flow is contained within the channel upstream of the 

diversion structure; that is, the design flow does not overflow the 

flood plain.

● The channel is no wider than 50 feet. Many of the structures can be 

designed for larger channels. 

The weir system referred to in several entries means a single structure 

composed of several weirs, each designed low enough that endemic 

species can jump or swim across them. The total height limit of a weir 

system is based on experience and judgment, considering the risk 

of failure during large floods. For permanent log and rock structures, 

weirs are limited to about a 6-foot drop height, while for the stronger 

concrete and steel structures, the limit is 12 feet because their risk 

of failure is lower. Also, 12 feet is a practical limit on the height of a 

structure before a geotechnical feasibility study needs to be done as 

part of the design. Adjustable weir heights are intermediate because 

they are normally placed on a concrete sill that lowers their risk of failure 

to something approaching an all-concrete weir. When estimating an 

acceptable structure height at individual sites, planners should evaluate 

both the consequences of possible failure as well as the risks. If the 

diversion requires a higher structure, consider moving the point of 

diversion upstream. Figure 4.30 shows a weir system—a pool and chute 

installation (A), which replaced a concrete drop structure impassable 

to endemic fish (B). See section 5 for an introduction to upstream fish 

passageways such as this. More detailed information about fishways can 

be found in Bates and Love (in preparation). 

4.5 Diversion Structure Applicability
98

Planning and Layout of Small-Stream Diversions

Figure 4.30—(A) Fish-passable pool and weir diversion structure constructed 

in 2008 on East Fork Birch Creek, OR. (B) The old check structure at the same 

site. 

B

A
99

Chapter 4—Diversion Structures

Structure 

Type

Rock Weir 

(full width)

Rock Ramp

(full width)

Cross 

Vane/ Barb 

(partial 

width)

Log/Timber 

Weir1

Concrete/

Steel Weir

Stop Log

Air Bladder

Tilting Weir

Channel 

Width 

(ft)

4 to 504 to 504 to 504 to 504 to 502 to 50

Up to 50

8 to 50

Maximum 

Drop 

Across 

Diversion 

Structure

(ft)

6 ft. total 

across 

a series 

of weirs 

(a weir 

system)

2 ft.(drop 

measured 

at bank)

6 ft. as part 

of a weir 

system

12 ft. as 

part of a 

weir system

8 ft.

10 ft.

Bank 

Height

(ft)

3 to 16

Channel 

Slope

(%)

0.1 to 5

0.1 to 10

0.1 to 5

Required 

Bank 

Stability

Medium

Medium +

LowLow

Range of 

Instream 

Flows

(cfs)

10 to 6,00050 to 6,000

2 to 2,500

2 to 10,00010 to 6,000

2 to 2,500

Qdiverted/

Qinstream

(%)

907595

100

9095

Acceptable 

Sediment 

Load

HighHigh

Medium

Size of 

Passable 

Debris 

(wood)

Permanent Weirs Adjustable Weirs

Table 4.2—Diversion structure suitablity for various site characteristics
100

Planning and Layout of Small-Stream Diversions

Pumps

Structure 

Type

Centrifugal

Propeller

Turbine

Channel 

Width 

(ft)

Up to 50

8 to 50

Maximum 

Drop 

Across 

Diversion 

Structure

(ft)

10

Maximum 

lift <30

Maximum 

lift VERY 

HIGH

Bank 

Height

(ft)

3 to 16

Bank 

should 

be high 

enough 

to protect 

electrical 

panels and 

controls 

from 

flooding.

Channel 

Slope

(%)

<2<2

Required 

Bank 

Stability

High, 

because 

of the 

significant 

infrastructure 

investment 

at pump 

stations

High, 

because 

of the 

significant 

infrastructure 

investment 

at pump 

stations 

Range of 

Instream 

Flows

Sufficient 

depth is 

required 

for pump 

operation. 

Pump 

must be 

protected 

from 

flooding.

Sufficient 

depth is 

required 

for pump 

operation. 

Qdiverted/

Qinstream

(%)

9090

Acceptable 

Sediment 

Load

Silt/clay 

load: Low to 

Medium

Sand load: 

Low (sand 

damages 

bearings 

and 

impeller).

High

Silt/clay 

load: Low to 

Medium

Sand load: 

Low (sand 

damages 

bearings 

and 

impeller).

Size of 

Passable 

Debris 

(wood)

3⁄4” and

less

4” and

less

Table 4.2—Diversion structure suitablity for various site characteristics (continued)
101

Chapter 4—Diversion Structures

Infiltration Gallery

Structure 

Type

Submersible

Infiltration 

Gallery

Channel 

Width 

(ft)

8 to 50

Maximum 

Drop 

Across 

Diversion 

Structure

(ft)

Maximum 

lift very 

high

Depends on 

site

Bank 

Height

(ft)

Bank 

should be 

high 

enough 

to protect 

electrical 

panels and 

controls 

from 

flooding

<12 

Bank 

excavation 

is required 

to connect the gallery 

to the

pump. 

>12 

Excavation 

is 

impractical.

Channel 

Slope

(%)

<2

>0.2

Required 

Bank 

Stability

High, 

because 

of the 

significant 

infrastructure 

investment 

at pump 

stations.

High, 

because 

of the 

significant 

infrastructure 

investment 

in gallery 

and pump.

Range of 

Instream 

Flows

Sufficient 

depth is 

required 

for pump 

operation

Any

Qdiverted/

Qinstream

(%)

90

Acceptable 

Sediment 

Load

Silt/clay 

load: Low to 

Medium

Sand load: 

Low (sand 

damages 

bearings 

and 

impeller).

Low—clays, 

organics, 

and other 

fines can 

plug the 

gravel filter.

Size of 

Passable 

Debris 

(wood)

3⁄4” and 

less

Table 4.2—Diversion structure suitablity for various site characteristics (continued)

Pumps
102

Planning and Layout of Small-Stream Diversions

Maximum drop across a diversion structure. For a stable rock weir, 

series of weirs, ramp or riffle experience shows that 6 feet is the largest 

safe drop before a retaining structure would be needed. If a diversion 

requires a higher check, consider moving the point of diversion upstream, 

or use a concrete or steel structure. The limit of 12 feet for a concrete 

or steel structure is a practical limit on the height of a structure before a 

geotechnical feasibility study should be done as part of the design. For 

pumps, this column is the maximum lift height. Single weirs should be 

limited to heights endemic swimming species can jump. 

Bank height. Where banks are lower than 3 feet, overflow is likely 

to be frequent, putting the diversion at risk of being outflanked during 

high flows. Banks higher than 16 feet require very long bank keys 

(as a general rule, a bank key is twice as long as the bank is high). 

That amount of excavation could cause an unacceptable amount of 

disturbance to the riparian area. For infiltration galleries, 20 feet is a 

rule of thumb beyond which the amount of bank excavation required to 

connect the gallery to the pump or ditch would be impractical. 

Channel slope. Where several weirs are constructed in series to allow 

for fish passage, individual weir fills coalesce on slopes steeper than the 

indicated upper limit, and the structure would effectively become a rock 

riffle or ramp. For pumps in channels steeper than indicated, it can be 

difficult to establish and maintain a sump for the pump, or sufficient water 

depth for the pump suction. 

Structure Stability

Table (T4.2) Notes
103

Chapter 4—Diversion Structures

Required bank stability. The terms used to describe required bank 

stability are relative. Required bank stability is designated intermediate or 

medium for rock structures because when minor erosion occurs, individual 

rocks can move and adjust to the new bank conformation. Wood structures 

should be placed where banks have medium or higher stability because 

they cannot adjust like rock, yet are permeable so that surrounding soil 

materials are subject to erosion. Low bank stability is acceptable for 

concrete and steel structures because they are impermeable and nearly 

nonerodible. 

Range of instream flows. Lower limits reflect the permeability of each 

structure type; the more permeable the structure, the higher the flow 

must be to permit effective diversion. Upper limits reflect the strength or 

durability of each structure type during high flows.

Maximum percent instream flow possible to divert. For weirs, this 

depends on permeability of the dam. For any screened diversion, whether 

weir or pump station, some bypass flow is required to sweep the screen 

clear of debris. 

Acceptable sediment load. This refers to the ability of the structural 

materials to withstand abrasion and battering by sediment in transport, 

or deposition of fine sediment in hinges. It does not address the issue of 

sedimentation in the backwater pool upstream of the structure.

105

Chapter 5—Fish Protection at Diversions

Diversions can affect fish and fish habitat in a variety of ways. For 

example, they reduce the amount of water in the stream, which reduces 

the available aquatic habitat; the smaller amount of water in contact with 

streambed gravels exposed to the sun can increase water temperature 

downstream; diversions also may increase sediment loading if they 

contribute to accelerated bank or bed erosion. Techniques for limiting 

some of these effects have been discussed in the previous sections 

dealing with the components of diversion infrastructure. 

Diversions also directly affect fish movement in both the upstream and 

downstream directions. This chapter describes commonly used fish 

screens and bypass systems—technologies used to protect fish moving 

downstream from becoming entrained and trapped in the ditch or pipe. 

The second part of the chapter discusses fish ladders, natural channel 

design, and other methods of providing passage around the diversion for 

fish moving upstream. 

Before considering fish passage improvements at a diversion, take 

a big picture look at water availability and other risks for fish in the 

system. Is there enough water for fish to fulfill their lifecycle needs? In 

the case of migratory fish, are there other barriers downstream? If there 

are unresolved Endangered Species Act issues that could result in 

elimination or reduction of the diversion, is an investment in fish passage 

warranted?

Fish screens are structures that physically prevent fish from moving into 

the diversion ditch (figure 5.1). Other barrier or fish guidance systems 

exist, such as electro-shock barriers, air bubble curtains, and louver 

panels, but these systems rely on fish avoidance and are generally 

considered experimental by fish and wildlife agencies (NMFS 2008) (see 

sidebar, Behavioral Barriers).

Screening fish from diversions is more difficult than one would think, 

because organic materials (twigs, algae, leaves, fine organic particles) in 

the water tend to clog the small screen openings. Screens are designed 

to have a large total open area—large enough that as water accelerates 

to go through the screen openings, fish will not be pinned to the surface. 

If part of the screen is blocked by debris, water accelerates more to get 

through the restricted open area, increasing the risk of pinning fish to the 

screen. Therefore, a cleaning mechanism is an essential part of screen 

design and operation (figure 5.2). Passive screens—those without any 

cleaning mechanism—exist but are sized considerably larger because of 

the tendency to clog. Generally, passive screens are used only where: (1) 

the stream is steep so that sweeping water velocity past the screen is fast 

enough to keep it clear and/or (2) where debris in the stream is scarce. 

5.1 FISH SCREENS AND FISH SCREEN BYPASS SYSTEMS

Chapter 5—Fish Protection at Diversions
106

Planning and Layout of Small-Stream Diversions

Figure 5.1—Looking downstream at double rotary drum screen installation on 

Fourth of July Creek diversion, Salmon River Basin, ID.

Figure 5.2—Rotatingdrum screen coated 

with aspen leaves in 

the fall. The screen’s 

rotation should lift 

the leaves over and 

wash them off the 

downstream side, but 

clogging occurred fast 

here. Flow passing 

through the drum 

decreased so rapidly 

that the paddlewheel 

stopped, stopping the 

drum rotation. After 

this photo was taken, 

a water measurement 

flume located 

downstream of the 

screen was removed. 

The screen gained 6 

inches of head as a 

result, and the problem 

is considered fixed. 

Fish Haven Creek, 

tributary to Bear Lake, 

ID. October 2009.

Behavioral Barriers

Air-bubble curtains—

formed when compressed 

air is released through 

small holes in a pipe or 

conduit—tend to guide fish 

away or past entrances 

to diversions. Louvers 

are bar-shaped pieces 

placed like overlapping 

shingles. Water that flows 

through the louvers must 

turn more than 90 degrees 

into the diversion and 

fish are expected to pass 

them by. Information on 

electro-shock barriers can 

be found at <http://www.

smith-root.com/barriers>.
107

Chapter 5—Fish Protection at Diversions

Fish screens are placed at or near the head of the diversion ditch to 

separate fish and debris from the diverted water, and protect fish from 

injury or entrainment in the ditch. Screens placed in the ditch return fish 

and debris to the stream channel via a bypass channel or pipe, which 

should reenter the channel at a safe discharge point downstream of the 

diversion structure (see figure 1.2). 

During the site assessment, consider what type of screen might be used 

and where it might be located (also see section 5.1.5). As you will see in 

this chapter, screens have different tolerances for incoming debris and 

water level variations, and they vary in the amount of bypass flow needed 

to sweep debris away (table 5.1). Generally, they must be located at a 

point on the ditch where a bypass can be constructed to take fish back to 

the main channel. 

Occasionally, screens are placed at the head of a diversion ditch without 

need for a bypass, but this only works where plenty of water exists to 

sweep fish, debris, and sediment away from the screen. Great care is 

needed with screen design and operation in these locations because 

debris and sediment can clog the screen and interrupt diversion 

operations. These screens also are at risk of damage by floating debris, 

unless a trash rack is placed in front of them. In addition, the velocity at 

which water enters the screen must be low enough to protect fish from 

being pinned to the screen. Flow in many small streams in the West is 

over-allocated; and at downstream sites, flow remaining in the channel 

may be insufficient to sweep a point-of-diversion screen effectively. 

Cleaning can be done by hand, but the consistent attention needed is 

usually more than most water users are able to maintain. 

If a screen is located on an active flood plain, the potential for a flood 

to overtop it is an additional design consideration. There are many 

other design elements that the design engineer will bring into the mix. 

Here we discuss only those items that planners and water users should 

think about as they assess a site for ways to protect aquatic resources 

and maintain or improve diversion stability. Consult the Washington 

Department of Fish and Wildlife (WDFW) “Fish Protection Screen 

Guidelines for Washington State” (WDFW 2000) for detailed information 

about screens commonly used in the west, as well as assessment, 

location, and design. WDFWs guide was written to ensure compliance 

with the National Marine Fisheries Service screening criteria for 

anadromous salmonids, but it contains a wealth of information and is a 

good starting point for understanding fish screens and considering how to 

protect fish in other locations as well. 
108

Planning and Layout of Small-Stream Diversions

In the context of small 

diversions, fish screens 

can seem costly to install 

and maintain. The water 

user’s priority is likely to 

be the consistency and 

reliability of diversion flow 

rather than fish protection. 

Where the protection 

of fish populations is a 

resource management 

goal, State and Federal 

agencies generally provide 

assistance with screen 

design, installation, 

and occasionally even 

maintenance. 

Some considerations for selecting a screen

1. Is there a type of screen familiar and accepted by the local 

irrigation community?

2. How much flow will be screened? Some types of manufactured 

screens are available for capacities under 10 cubic feet per second 

(cfs).

3. How much bypass flow is available to screen the water? Screens 

vary in their needs for bypass flow. Moving screens require the least 

bypass flow—only enough to convey the fish back to the channel. 

Bypass flow can be as low as 0.6 cfs for rotary-drum screens. 

Passive screens can require bypassing as much as 40 percent or 

more of the screened (diverted) flow. 

4. Will the water serve a sprinkler or siphon-tube irrigation system? 

These systems cannot tolerate the leaves and small debris that 

moving screens allow into the diversion. If moving screens are used, 

the water will need to be screened again. On the other hand, if the 

screened water flows a long distance in an open ditch, it would need 

to be screened again anyway.

Criteria governing the size of screen openings exist only for anadromous 

fish (NMFS 2008), but the same criteria have been adopted by several 

Western States for resident fisheries. The NMFS criterion for opening 

size (1.75 millimeters) protects salmonids as small as fry from passing 

through the screen. The criterion is not small enough to protect fry of all 

fish species; sucker fry, for example, are smaller. Even where screening 

is not mandated by law, if you elect to screen, it’s recommended you 

use the NMFS criteria for both screen size and approach velocity. The 

low approach velocity (0.4 feet per second directly toward the screen) 

protects the screen from small twigs and sediment being caught in 

the screen openings. Debris can still plaster the screen temporarily 

(figure 5.2), but it can usually be removed by sweeping or floating it off. 

Openings larger than the NMFS criteria increase the potential for floating 

material to clog the openings, which requires time-consuming manual 

cleaning. 
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Chapter 5—Fish Protection at Diversions

Screens are either fixed in place, or they move as part of the cleaning 

process. A fixed screen is sealed in place and does not move, although 

brushes or other cleaning components may move over it. In a moving 

screen, seals and brushes close gaps between the moving screen and 

its housing, preventing the fish from entering the diversion ditch through 

those gaps. 

Fixed screens include:

● Plate screens cleaned by bursts of air (air burst) or water (water 

backwash). 

Figure 5.3—Pressure backwash flat plate fish screen at the end of a pump 

suction. This intake is in a channel undergoing reconstruction after an 

impoundment was removed. Garden Creek, Bonneville County, ID. Photo 

courtesy of Matt Woodard, Trout Unlimited.

● Plate screens cleaned by brushes (common in California).

● Plate screens cleaned by water flowing over and off the screen.

Moving screens include:

● Rotary-drum screens (commonly installed in the Pacific Northwest) 

(figure 5.2).

● Traveling-belt screens (common in municipal and industrial water 

intakes).
110

Planning and Layout of Small-Stream Diversions

Table 5.1 in section 5.1.4 compares different types of screens with 

respect to various characteristics that affect screen selection. Table 5.2 

summarizes installation and operations and maintenance needs and the 

effort required for each type. 

5.1.1 Fixed-plate Screens

Fixed screens can be vertical, inclined, or horizontal. They have the 

advantage of being able to work over a wide range of flows, but they 

need substantial bypass flow to carry away the debris cleaned off the 

screen surface. They have smaller space requirements than moving 

screens and generally can be fit into whatever shape is required by the 

diversion site layout. They also can be designed to avoid entraining fish 

even when overtopped during a flood; either the walls of the screen can 

extend above the expected flood elevation, or the screen can be covered 

to prevent fish from washing in. 

Horizontal flat-plate screens (figure 5.4) are passive; that is, there is no 

cleaning mechanism other than the sweeping flow itself. The surface 

area of a passive screen is determined by the desired diversion rate 

(i.e., the rate of water inflow through the screen) and by the acceptable 

water velocity through (normal to) the screen vis-a-vis fish impingement. 

As a rule of thumb, the area of a passive screen should be at least 15 

to 20 ft2

 per cfs diverted. Again, the National Oceanic and Atmospheric 

Administration NMFS criteria (1.75 mm (1/16 inch) holes or slots) are 

recommended even where screening is not regulated. The criteria 

minimize fish entrapment, and they also help keep the plugging potential 

down.
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Chapter 5—Fish Protection at Diversions

Figure 5.4—Horizontal flat-plate screen. Upper Fish Haven Creek, Bear Lake, ID. (A) Photo was taken during 

installation. The view is upstream looking toward the headgate. In this Farmers’ Conservation Alliance screen, 

the partially shadowed screen is on the left, with some debris on top. Boards in the middle control how much 

flow exits toward the diversion ditch, which is out of sight behind the photographer. (B) This view is looking 

downstream. When the screen is functioning, fish pass over the screen, and out the bypass pipe seen in the 

background, right. These screens require substantial bypass flow. At least 6 inches of fast-moving water is 

needed to protect the fish from scraping on the screen, and to sweep the screen of debris. 

A

fish bypass outlet

B
112

Planning and Layout of Small-Stream Diversions

5.1.1.1	Cleaning systems for fixed-plate screens

Vertical and inclined screens can be passive or they can be cleaned by 

air burst, water backwash, or wiper systems, all of which require power. 

For wipers, the most common power sources are a paddlewheel turned 

by the water flowing in the ditch (figure 5.5) and, for larger diversions, 

electric power from the grid or the sun. Paddlewheel-driven cleaning 

systems must have enough flow to continuously turn the paddlewheel or 

the screen can plug and fail to allow water into the diversion. Flat ditches 

(in wetlands and other flat gradient systems) require special attention to 

water velocities and available energy to drive paddlewheel systems. If a 

site does not provide the energy needed to operate the wipers, fish will 

be impinged on the screen as it clogs, and diversion flow will decrease or 

stop.

Figure 5.5—Inclined-plate fish screen cleaned by wipers powered by a 

paddlewheel, Thomas Fork, Bear Lake County, ID. Flow is away from the 

photographer. This screen serves a 40 cfs diversion. Design and construction 

cost $150,000 in 2008.

Debris damage to wipers is a common way for them to fail.
113

Chapter 5—Fish Protection at Diversions

Air-burst and water-backwash systems (figure 5.6) have high power 

requirements, and screens that use them are more costly to install than 

paddlewheels. This is not only because of the need to install a solar 

or grid power supply; the air compressor or water pump also can be 

costly. Pressure water-backwash screens for up to 5 cfs are available 

commercially. 

Figure 5.6—Water-burst backwash system operating on one of several screens 

at bank toe on Kalapuya River, OR. This screen feeds water to a pump sump for 

the Brownsville municipal water system. This screen also is pictured in figures 

4.24 and 4.26.
114

Planning and Layout of Small-Stream Diversions

5.1.2 Moving Screens

Moving screens—either rotary-drum (figures 5.7 and 5.8) or traveling-belt 

screens (figure 5.9)—clean themselves as they move. These screens do 

not need as much bypass flow to carry debris away as fixed screens do, 

because they are cleaned by water flowing through them. As the drum or 

belt turns, it carries debris caught on the upstream side over the top of 

the screen, where it washes off, and continues down the diversion. If the 

water distribution system at the point of use cannot tolerate debris (e.g., 

sprinklers, drip), a second screen would be required. 

Figure 5.7—Three-bay rotary-drum screen on Salmon River, ID, 2008. Each 

water wheel powers one drum screen. These permanent concrete installations 

were common in Idaho until the less expensive, prefabricated versions were 

developed.
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Chapter 5—Fish Protection at Diversions

Figure 5.8—Rotary-drum fish screen on Elk Creek, Salmon River Basin, ID. This 

type of modular setup with a trash-rack and rotary-drum screen powered by a 

paddlewheel is very common in mountain streams in Idaho and other Western 

States in anadromous fish habitat.
116

Planning and Layout of Small-Stream Diversions

Figure 5.9—Traveling-belt fish screen, Lytle Creek, San Bernardino County, CA, 

protects a municipal water intake.

Rubber seals or brushes—next to and touching the edges of the moving 

component—keep fish from getting past the drum or belt. One of the 

most common ways moving screens fail is by cracks or holes developing 

in the seals and allowing fish through the screen. The bearings and seals 

in moving screens last much longer if they are not exposed to silt and 

sand. Installing a sump in the ditch upstream of the screen to trap the 

sediment, or placing the screen above the floor of the structure both can 

reduce the screen’s exposure to fine sediment.

The rotary-drum screen only works when water levels are within a 

restricted range, so it requires more water control than other screens. 

The usual method of flow control is a submerged orifice headgate at 

the point of diversion. Rotating drums are more expensive to install 

than fixed screens, but they are probably the most well-developed and 

reliable screening technology in common use today. They are preferred 

by State fisheries agencies in Washington, Idaho, and Oregon. At least 

one provider (located in Idaho) can supply prefabricated rotating-drum 

screens for up to 10 cfs. 
117

Chapter 5—Fish Protection at Diversions

5.1.3 End-of-pipe Screens

End-of-pipe screens usually are used with pumps. Self-cleaning pump 

screens (air or water backwash systems) can be highly reliable, and 

some are designed for fish screening (figures 4.28 and 5.3). Generally, 

the only maintenance these screens require is replacing a bearing every 

1 to 2 years. 

Passive end-of-pipe screens for up to 1 cfs are available commercially. 

They are useful where only a small fraction of streamflow is diverted. 

Passive screens located near the stream bottom tend to plug or become 

buried, and can be damaged by abrasion. They are generally suspended 

above the streambed to protect them (figure 5.10). 

Figure 5.10—End-of-pipe fish screen, Williams Creek, Sawtooth National 

Recreation Area, ID. This appears to serve a gravity diversion rather than a 

pump. 

5.1.4 Screen Comparisons
118

Planning and Layout of Small-Stream Diversions

Type of 

Screen

Air-Burst 

Backwash

Water 

Backwash

Wiper 

Screen

Bedload 

Fines Silt 

and Sand

Screen 

can be set 

above the 

floor. (Very 

Good)

Variable 

Water 

Surface 

Elevation

Tolerate 

large 

variability 

in incoming 

flow. 

(Very Good)

Floating 

Trash

Floating 

debris 

must be 

bypassed 

with 

significant 

bypass 

flows. 

Handles 

well with 

significant 

bypass 

flows. 

(Fair)

Limited 

Space

Can be fit 

to nearly 

any shape. 

(Very Good)

Head Loss 

Across 

Screen 

System

Screen 

operates 

well with 

low head 

differential. 

(Very Good)

Screen 

operates well 

with low head 

differential. 

Drive 

system uses 

approximately 

the same 

energy as a 

rotary drum 

system.

Sub 

Freezing 

Conditions

Can be 

set up to 

operate in 

freezing 

conditions.

(Good)

Can be 

set up to 

operate in 

freezing 

conditions 

(Stop wiper 

arms–use 

as a passive 

fixed-plate 

screen).

(Poor)

Short 

Duration 

Floods

Can be 

setup to 

protect fish 

in a flood 

situation.

(Very Good)

Energy 

Requirement

High

Low

Widespread 

Acceptance 

of Fish and 

Wildlife 

Agencies

Yes

Pacific 

Northwest 

and 

California

Table 5.1—Advantages and disadvantages of different screen types. The “good” and “poor” labels rate each screen type in comparison to the others for each variable in the table

FIXED PLATE SCREENS
119

Chapter 5—Fish Protection at Diversions

Type of 

Screen

Horizontal 

Flat Plate

Passive 

end-of-pipe 

screen

Bedload 

Fines Silt 

and Sand

Can 

accumulate 

grains of 

sand in 

screen; sand 

must be 

removed to 

protect fish. 

(Fair)

Must be 

suspended 

above the 

stream 

bottom to 

prevent 

accumulation 

of sediment. 

(Fair)

Variable 

Water 

Surface 

Elevation

Fish 

protection 

depends on 

water depth 

over screen.

(Variable 

rating 

depending 

on state 

requirements 

for water 

depth over 

screen.)

Must be 

submerged. 

(Good in 

deep pools.)

Floating 

Trash

Floating 

debris 

must be 

bypassed 

with 

significant 

bypass 

flows. 

Handles 

trash 

well with 

significant 

bypass 

flows. 

(Fair)

Limited 

Space

Can be fit 

to nearly 

any shape. 

(Very Good)

Generally 

very small 

and easy 

to fit into 

variety of 

stream

locations.

(Very good)

Head Loss 

Across 

Screen 

System

Operates well 

with 

0.1 ft 

across 

screen.

(Very Good)

Operates 

well with 

0.1 ft head 

loss across 

screen

(Very good)

Sub 

Freezing 

Conditions

Operates 

well under 

freezing 

conditions 

as long as 

water is 

moving over 

screen.

(Good)

Good

Short 

Duration 

Floods

Operates 

well. 

Continues 

to protect 

fish.

(Very Good)

Enclosed

screen

continues

to protect

fish.

(Very good)

Energy 

Requirement

Low

(Very good)

None except 

hand 

cleaning.

(Very good)

Widespread 

Acceptance 

of Fish and 

Wildlife 

Agencies

No. 

One type is 

patented and 

accepted 

with special 

conditions in 

Oregon.

Case 

by case.

Table 5.1—Advantages and disadvantages of different screen types. The “good” and “poor” labels rate each screen type in comparison to the others for each variable in the table (continued)

FIXED PLATE SCREENS
120

Planning and Layout of Small-Stream Diversions

Type of 

Screen

Rotary 

Drum

Traveling 

Belt

Bedload 

Fines Silt 

and Sand

Must have

a sump in 

the ditch 

and/or 

a raised 

screen 

(5-6 inches) 

and a free 

flowing 

bypass. 

(Fair)

Variable 

Water 

Surface 

Elevation

If 

overtopped, 

fish can 

pass over 

the drum. 

(Poor)

Very Good

Floating 

Trash

Passes 

over drum. 

(Very Good)

Carried 

over belt. 

(Very Good)

Limited 

Space

Configuration 

can be 

adjusted to 

fit most 

sites. 

(Fair)

Application 

is limited to 

deep water 

(not shallow 

ditches). 

Screen can 

be very 

compact 

when water 

is deep.

(Good)

Head Loss 

Across 

Screen 

System

Rotary drum 

can operate 

under head 

drop of 

approximately 

0.2 ft.

(Good)

0.1 ft.

(Good)

Sub 

Freezing 

Conditions

Drum must 

be raised in 

extended 

sub-freezing 

conditions. 

(Poor)

Belt must 

be raised in 

extended 

sub-freezing 

conditions. 

(Poor)

Short 

Duration 

Floods

Will not 

protect 

fish when 

overtopped. 

(Fair)

Can be 

set up to 

protect fish 

in a flood 

situation.

 (Very Good)

Energy 

Requirement

Low power 

requirements 

can be met by 

paddlewheel, 

grid, or solar 

electric drives. 

(Good)

Generally 

solar or AC 

electric drive. 

(Fair)

Widespread 

Acceptance 

of Fish and 

Wildlife 

Agencies

Pacific 

Northwest

Moderately 

well 

accepted 

in Pacific 

Northwest 

and 

California.

Table 5.1—Advantages and disadvantages of different screen types. The “good” and “poor” labels rate each screen type in comparison to the others for each variable in the table (continued)

MOVING SCREENS
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Chapter 5—Fish Protection at Diversions

Table 5.2 provides additional information about installation costs, 

operations and maintenance requirements, and susceptibility to damage 

from ice and from sediment and debris loading. Note that diversion 

installations are also frequently at risk from vandalism, beaver and other 

animal activity, tree root growth, and sometimes wildfire. 

If maintenance is neglected, any screen can plug with debris, decreasing 

the diversion flow and putting fish at risk of impingement. Ideally, fish 

screens should function without operator input for 12 hours or more; 

however, on days when the stream is moving lots of sediment and 

debris, most screens can benefit from attention more than once per day. 

Screens in recently burned watersheds may need even more frequent 

attention. Typical screens designed and installed by State fish and 

wildlife agencies function for several days without operator input. 

Table 5.2—Screen installation, operation and maintenance

INSTALLATION OPERATION AND MAINTENANCE

Screen

Type

Air-Burst 

Backwash

Water 

Backwash

Wiper Screen

Horizontal Flat 

Plate Screen

Comparative

cost

Medium

Medium

Challenges

Dewatering 

may be 

required in 

areas with 

high ground 

water tables.

Power 

requirements.

Dewatering 

may be 

required in 

areas with 

high ground 

water tables.

Complicated 

systems.

Space/

easement 

restrictions.

Portability

Portability 

depends on

(1) Screen size 

(how much 

flow will be 

screened).

(2) Weight of 

materials used 

(concrete, steel, 

plastic, wood, 

aluminum).

Maintenance

needs

Remove debris 

from front 

of screen or 

bypass

Backwash 

machine 

bearings 

require annual 

maintenance.

Remove debris 

from front 

of screen or 

bypass.

Lubricate 

bearings 

weekly.

Remove debris 

from bypass.

Susceptibility

to damage

Resistant.

Susceptible to 

large debris.

Sediment 

deposition: screen 

must be removed 

to clear sediment.
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Planning and Layout of Small-Stream Diversions

Table 5.2—Screen installation, operation and maintenance (continued)

INSTALLATION OPERATION AND MAINTENANCE

Screen

Type

Rotary Drum

Traveling Belt 

Screen

End-of-Pipe 

Screen with 

Backwash

Passive 

End-of-Pipe 

Screen

Comparative

cost

Medium

Low

Challenges

Dewatering 

may be 

required in 

areas with 

high ground 

water tables.

Complicated 

systems.

Space/

easement 

restrictions.

Installing 

during high 

flows.

Portability

Portability 

depends on

(1) Screen size 

(how much 

flow will be 

screened).

(2) Weight of 

materials used 

(concrete, steel, 

plastic, wood, 

aluminum).

Very portable.

Maintenance

needs

Remove debris.

Weekly 

lubrication.

Weekly 

lubrication and 

debris removal 

can protect 

pump from 

burnout.

Check 

frequently for 

debris removal 

needs.

Susceptibility

to damage

Sediment 

deposition: screen 

must be removed 

to clear sediment.

Icing.

May wash away 

during high flows.
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Chapter 5—Fish Protection at Diversions

5.1.5 Common Causes of Screen Failure 

In general, most fish screen failures are caused by power failures or 

mechanical defects, such as:

● Debris damage to cleaning mechanism.

● Holes allowing fish past screen.

● Inadequate fall in the water surface to drive paddlewheel systems.

Operator error or inattention and lack of timely maintenance contribute 

to screen failures. Where screen functioning is dependent on water 

level, for example, the operator may be unable to adjust the headgate 

as frequently as needed, especially during summer storms. An example 

of operator error occurred on a mountain stream during a storm event, 

when the operator closed the headgate slightly to avoid drawing too 

much water into the ditch. The smaller opening created a large head 

difference that sucked in sediment and buried the screen. 

Designers can limit failures by designing systems appropriate to the 

operator’s abilities and interests. In addition, using screens from proven 

suppliers will assist in avoiding these problems. State fish and wildlife 

agencies often have screen shops of their own, as well as lists of 

recommended suppliers for off-the-shelf screens.

5.1.6 Fish-screen Bypasses

The function of the screen bypass is to return fish and water to the main 

channel. Fish bypass design has been standardized for anadromous 

fish screens meeting NOAA NMFS criteria (NMFS 2008). The bypass 

design parameters include the minimum conduit size, minimum bend 

radii, maximum velocity, as well as other features that protect fish as they 

approach and pass through the bypass. 

Fish-screen bypasses are either open channels or pipes. Pipes are 

inexpensive and allow equipment and people easier access to the area 

between the screen and the stream. They also protect fish from predation 

from above (birds) and are less prone to freezing. It can be difficult to 

install a pipe so that water velocity is slow and deep enough to float fish 

without injury or stress, yet fast enough to transport sediment through the 

pipe. Sediment deposition in pipes is a common problem, as is floating 

debris. Nonetheless, pipes are much more common bypasses. The 

bypass pipe from a horizontal screen is visible in figure 5.5 (b), center 

right. The pipe outlets into a small pool, constructed for the purpose. 
124

Planning and Layout of Small-Stream Diversions

Upstream fish passage is an important component of fish stock health. 

Adult anadromous fish migrate long distances to spawn, and resident 

fish may move large or small distances to mate, find food, escape 

undesirable flow or temperature conditions, and recolonize areas 

depopulated by flood or other catastrophes. Diversion structures can 

block upstream movement of some or all species and life stages of fish 

either because the drop across the weir or dam is too high to jump, or 

water velocity is too fast. Each barrier either prevents access to habitat, 

or stresses the fish that do pass successfully. In numerous cases, fish 

have been observed swimming into habitat long blocked by a barrier 

almost as soon as it was removed. Diversions also can prevent or 

impede upstream fish passage when flows passing downstream of 

the diversion are diminished to a point where upstream movement is 

impossible (see figure 1.9). Even passable diversions can contribute to 

an eventual passage problem downstream via their cumulative effect on 

diminished streamflow.

The ideal diversion does not require a channel-spanning dam structure to 

divert water into a ditch or pipe. Where the water surface does not have 

to be elevated more than 2 feet, the control structure itself may be made 

passable for many fish. Rock ramps similar in slope and bed character 

to natural reaches on the same stream, and rock or log weirs similar 

in height to natural steps are most likely passable by fish accustomed 

to moving around in that stream (see section 4.1.1). Many diversions 

do require a taller structure, however, and upstream passage should 

be provided wherever possible. Keep in mind that off-channel fishways 

require water, typically 1 to 2 cfs. 

Upstream passage may be provided by a constructed fish ladder, a 

constructed open channel, or by an altered location or height of the 

diversion structure. What type of strategy or structure will fit and do the 

job depends on the total elevation drop, the target species, and the space 

available to accommodate a fishway or ladder.

5.2.1 Relocating the Diversion 

Where the downstream channel has scoured or incised so fish cannot 

pass, a diversion can be relocated upstream if space and access 

permissions allow. An upstream location would be higher in elevation, 

and might be able to supply water to the ditch without the need to 

construct a channel-spanning dam that would block fish movement. 

5.2 UPSTREAM FISH PASSAGE
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Chapter 5—Fish Protection at Diversions

There are some potentially harmful or inconvenient aspects to this 

option. 

● The ditch or pipe lengthens, increasing disturbed riparian area, 

the length of dewatered stream channel, and risks associated with 

possible lack of maintenance (e.g., ditch breakouts).

● If the current diversion dam is removed, a nickpoint may migrate 

upstream to the new point of diversion, beginning the entire cycle 

of diversion relocation again. Potential channel downcutting can 

often be mitigated with control structures, such as rock riffles or 

weirs.

In some cases, relocations can include combining points of diversion 

and/or piping the diverted water to the place of use to conserve water. 

Both strategies have positive effects that may outweigh the risks 

mentioned above. Note that if a point of diversion is changed, the 

State must be contacted. The altered point of diversion will need to be 

recognized in the water right.

All of the following types of engineered fish passage structures are 

located to one side of the main stream channel or adjacent to it. For fish 

to locate the downstream entrance to the fishway, the entry point should 

be very near the diversion dam or weir, and the amount of flow should 

be adequate to attract fish to the fishway. Fish may be unable to locate 

fishways at dams where fishway flow is small compared to flow over the 

dam or where the outlet is not at the dam. Care is needed in designing 

the entrances and exits of upstream passageways; failures are not 

infrequently due to undercutting and erosion at connection points to the 

stream. 

The following information about fishways is a very brief introduction to 

help readers recognize types of fishways encountered in the field. A 

fishway engineer should help to determine what style of fishway, if any, 

might be appropriate for upgrading a specific site. Good references for 

further reading about fishways are NMFS (2008) and WDFW (2000), and 

CDFG (2009).
126

Planning and Layout of Small-Stream Diversions

5.2.2 Seminatural Open-channel Fishways Designed for a 

Target Fish

These are side channels that generally are constructed with rock and/

or wood to emulate a mountain stream or cascade. Typically, grade is 

limited to 5 percent because sufficient resting areas (low-velocity pools 

or eddies) are difficult to achieve in steeper constructed channels. If 

the elevation difference across the diversion is too great for a straight 

channel at 5 percent or less, the site must have enough space to 

construct a longer channel (figure 5.11). Constructed channels have 

been used to provide passage around elevation drops of up to 15 feet. 

Depending on how similar the fishway is to reaches on the project 

stream, many species may be able to pass it, including fish that don’t 

jump, and species, such as lamprey, eels, crayfish, and salamanders.

Figure 5.11—Newly constructed open-channel fishway around diversion dam on 

Thomas Fork, a tributary of Bear Lake, ID. The dam in this photo is 6 feet high, 

and it backs water up 4 miles. Fishway grade is 3 percent. Stoplogs control flow 

in the fishway. During the first 2 years of monitoring, this new channel passed 

not only target salmonid species, but also several native fish species generally 

considered to be less adept swimmers, including sculpins, suckers, chubs, and 

over 15,000 speckled dace and redside shiners (Colyer 2010).

Channel stability for an open-channel fishway depends in part on bankstabilizing vegetation. Vegetation also is important as a source of cover 

for fish as they move through the fishway. The first few years, vegetation 

probably will need protection from browsing wildlife, fire, and flood. 
127

Chapter 5—Fish Protection at Diversions

Virtually all engineered fishways require water-control structures to 

maintain flow within the passable range for the fishway. Compared to 

pool-and-weir fish ladders, nature-like open channel fishways generally 

are wider with sloping banks, so their capacity is larger. They tend to be 

passable over a larger range of upstream water surface elevations and 

may require less careful flow control than ladders. Nonetheless, they 

do require flow control to avoid high, impassable velocities and channel 

erosion. 

5.2.3 Fish Ladders 

Fish ladders can pass a wide range of salmonid fishes, and with special 

attention (corner detailing, no abrupt edges, etc.), they can also pass 

lamprey. For the pool-and-weir and steep-pass ladders, adding an 

orifice at the bottom of each weir can allow the passage of nonleaping or 

bottom-swimming fishes.

Like open channels, ladders can function with a wide range of sediment 

loads. Often, moveable gates or orifices are placed near the bottom 

of the ladder channels to pass sediment. However, ladder functioning 

is highly susceptible to woody debris blockages. Debris can block fish 

passage and it can be difficult to remove. Fish ladders require either a 

water supply without much woody debris or daily maintenance to clear 

debris from the weir boards or trash rack if there is one. 

A challenge in fish ladder design is matching the ladder with upstream 

and downstream water surface elevations over the range of flows for 

the diversion season. If the designer’s estimates of main-channel water 

surface elevation at different flows are wrong, the ladder may dry up or 

drown at low and high flows. 

5.2.3.1	Denil and Alaska Steeppass Fish Ladders

These ladders are used mostly in Alaska and in the Northeastern 

United States. They are useful for steep stream gradients and can be 

prefabricated and transported to the site. The design was developed 

empirically, and testing has verified passability for salmonids. Lamprey 

successfully passed the temporary Denil ladder on the Clackamas River 

in Oregon during construction at the Rivermill dam (figure 5.12), and carp 

are known to have swum up a Denil on the Malheur Refuge in eastern 

Oregon. In general, however, these ladders do not provide adequate 

upstream passage for nongame native fish species, such as sculpins, 

minnows, or suckers.
128

Planning and Layout of Small-Stream Diversions

Denil and Alaska steeppass ladders are usually placed on grades 

between 16 percent and 25 percent, and range from 2 feet to 4 feet in 

width. Blades attached to the walls generate turbulence and create low 

velocity pathways that salmonid fishes use to swim up the ladder. 

Figure 5.12—Denil steeppass fish ladder. This ladder functioned during 

reconstruction work at the Rivermill dam on the Clackamas River, OR. 

Prefabricated steeppass ladders are sometimes flown into sites in 

the Alaskan backcountry. They also can be constructed onsite from 

wood, concrete, steel, or aluminum. They require frequent and diligent 

maintenance anytime debris is moving in the stream.

5.2.3.2	Pool-and-weir Fish Ladders

In these structures, water plunges or cascades through a series of weirs 

and pools, designed so the target fish can jump or swim through them 

at a controlled flow. Energy is dissipated (and velocity controlled) by 

turbulence generated as waterfalls over each weir. Pool-and-weir ladders 

are built of concrete, steel, or wood. They can be as narrow as 2 feet, 

or they can occupy the full channel width. Typically, grade is limited to 

10 percent because on steeper grades, building pools that effectively 

dissipate energy but do not collect sediment is difficult. These ladders 

are quite common, and they are usually site-specific designs constructed 

onsite. Often the weir plates have orifices that allow nonjumping or 

juvenile fish to move between the pools (figure 5.13). 
129

Chapter 5—Fish Protection at Diversions

Pool-and-weir fish ladders are very sensitive to variation in water surface 

elevations upstream and downstream of the structure. Such variations 

change the height of jumps across each weir and the volume and 

velocity of flow in the ladder. Flow is usually controlled by removable 

dam boards or stoplogs.

Figure 5.13—Pool-and-weir fish ladder built for spring-spawning Bonneville 

cutthroat trout, Cub River, tributary of Bear River, ID. (A) General view of the 

ladder looking downstream. Ladder is nearly dewatered at this time. (B) Looking 

upstream from the ladder entrance. When the ladder is functioning, the 1-foot 

weirs are overtopped and water plunges into the pools between them. Note the 

offset orifices cut into the bottom flashboard, which permit whitefish to swim 

through and rest in eddies behind the weirs. This ladder serves the diversion 

dam pictured in figure 4.3; its concrete wall is visible in the center-right of that 

picture.

A B
130

Planning and Layout of Small-Stream Diversions

5.2.3.3	Vertical-slot fish ladders

Vertical-slot ladders are similar to pool-and-weir ladders except that the 

weir plate does not extend across the entire width. Fish swim through a 

slot between two vertical weir segments or between the weir and the wall. 

Behind the weir are one or more eddies in which fish can rest. Again, 

grade typically is limited to 10 percent.

Vertical-slot ladder configurations are set for specific flow conditions, 

species, and life stages. They work through wide ranges of upstream and 

downstream water surface elevations; that is, waterflow through them 

does not have to be carefully controlled as with the steep-pass and pooland-weir ladders. They use large volumes of water (usually not less than 

30 cfs), so they are limited to larger diversions (figure 5.14).

Figure 5.14—Vertical-slot fish ladder, Santiam Water Control District diversion 

canal, OR.

Accessing diversion sites with heavy construction equipment and concrete 

trucks is a frequent problem, especially in narrow tributary valleys without a 

road near the site. Some types of fish passages can be constructed by hand 

or using materials brought in by ATV, as indicated in table 5.3. 
131

Chapter 5—Fish Protection at Diversions

Fishway 

Type

Pool-and-Weir

Denil and 

Alaska Steep 

pass

Vertical Slot

Comparative 

Installation 

Costs

High

Medium

High

Installation 

ChallengesDewatering. 

access for 

concrete truck.

Dewatering.

Precision 

installation. The 

exact shape 

of the weirs is 

very important. 

Most successful 

with concrete. 

Dewatering.

Portability

For small 

applications, can be 

prefabricated or built 

onsite of wood or 

steel. 

Portable for many 

small applications. 

They are not very 

heavy and can 

be carried by two 

people. In Alaska, 

they are flown into 

backcountry by 

plane or helicopter.

Not very 

portable.

Maintenance 

Requirements

Remove and 

reinstall stoplogs 

seasonally. 

Remove and 

reinstall blades 

annually and 

remove debris 

daily.

Remove debris 

at least weekly.

Impacts due 

to lack of 

O&M

Sediment and 

debris accumulate 

and can block fish.

Wood easily 

accumulates on 

blades, and can 

trap and block fish. 

This is a more 

acute problem for 

steeppasses than 

for pool-and-weir 

fishways.

Similar to 

steeppass ladders.

Susceptibility 

to 

Damage

Stoplogs/

blades can be 

stolen, eaten by 

beavers, and 

burned.

LowLow

Table 5.3—Fishway Installation and operations and maintenance
132

Planning and Layout of Small-Stream Diversions Fishway Type Constructed Channel— Semi-natural Open Channel Fishway Comparative Installation Costs Medium Installation Challenges Dewatering. Access for rock and debris removal. Portability Could be constructed with a small excavator depending on channel size. Maintenance Requirements Weekly or more often; adjust flow to proportion water between the stream, the constructed channel, and the ditch. Impacts due to lack of O&M Channel may take too much water from diversion. Downstream fish movement may be impaired by debris accumulation in fishway. Susceptibility to Damage Stabilizing bank vegetation can be damaged by fire, flood, vandalism, and beavers. Table 5.3—Fishway Installation and operations and maintenance (continued)
133

Chapter 6—Flow Measurement

Measuring the volume of water actually being diverted is increasingly 

important as demands on surface water multiply. The need for instream water for aquatic habitat and channel maintenance—virtually 

unrecognized when Western water law was set up—is a frequent point of 

contention especially where endangered or threatened aquatic species 

are present. Water measurement may or may not be required by the 

water master or other State authority. Flow measurement structures 

generally are installed downstream of the fish screen and its bypass, if 

present.

One of the challenges in ditch-flow measurement where the ditch is fairly 

flat (i.e., where there is not much head to deliver the water to the point 

of use) is that flow measurement devices expend some head. Available 

head at a site frequently drives the choice of measurement device. This 

chapter discusses three types of flow measurement devices commonly 

used in diversions.

● Sharp-crested weirs.

● Flumes.

● Submerged orifices.

Other flow measurement methods include current meters, acoustic flow 

measurement devices, and tracers. This guide does not discuss these 

methods because they are uncommon in ordinary field situations and 

require special equipment. They are used in unique cases, or for large 

canals. They all require an open-channel control section. 

An open-channel control section and staff gauge is a common method 

of measuring flow rate at stream-gauging stations. The control section 

is a straight, uniform, stable reach where flow rate (discharge) can 

be related reliably to water surface elevation (stage) (figure 6.1). The 

resulting stage-discharge rating can change if sediment deposits on 

the ditch bed, if the ditch scours, or if vegetation growth affects ditch 

flow. The rating should be recalibrated at several flows every year. This 

method could be useful for ditches with insufficient head (elevation drop) 

for measurements with a hydraulic structure. However, it is not used 

commonly for ditch-flow measurements because it requires instruments 

(current meter), expertise, and a substantial investment of time to 

maintain the rating. Some diversions do use them as indicators, but 

generally State water departments prefer the accuracy of measurement 

structures. 

Chapter 6—Flow Measurement
134

Planning and Layout of Small-Stream Diversions

Figure 6.1—Open-channel control section and staff gauge at USGS gauging site 

on an unnamed tributary of Bertrand Creek, near Lynden, WA (not a diversion 

ditch). Photo courtesy of Darrin Miller, USGS, Sedro-Wooley WA. This control 

section is not ideal because of its location downstream of a bend. Preferably, 

the control reach should be located on a straight section where downstream 

conditions are relatively unchanging.

The U.S. Department of the Interior’s Bureau of Reclamation “Water 

Measurement Manual” (USBR 2001) is the standard reference for all 

water measurement devices including those described in this guide. 

The information that follows is enough to select an appropriate type 

of measurement device if the existing one is dysfunctional or if none 

exists. It is not enough to design and construct a flume, weir, or 

orifice. Generally, a flume, weir, or orifice is designed by an engineer 

for the specific site and range of flow rates, and constructed to 

specifications. All measurement devices must be constructed and 

installed to specifications, or they will not be accurate (see for example 

Heiner 2009). The U.S. Department of Agriculture, Natural Resources 

Conservation Service or State cooperative extension services may 

be able to help private landowners. The Bureau of Reclamation helps 

irrigation districts with water measurement design, and it also has 

developed public access software (WinFlume) for designing flumes 

(Bureau of Reclamation 2009), although WinFlume does not produce 
135

Chapter 6—Flow Measurement

a detailed construction drawing. Western States have posted many 

irrigation water measurement Web sites that can help with selection 

and design. For example, Utah State University cooperative extension 

currently has posted a good, simple overview of measurement devices, 

prices, and sources of supply (Hill 1999). The Utah Division of Water 

Rights also has guidance for measuring flows (Adkins 2006).

What are they? A sharp-crested weir is a vertical plate or blade 

constructed to a standard design and installed perpendicular to flow 

in an open channel (figure 6.2). The weir is calibrated so that a certain 

height of water in the pool upstream of the weir blade corresponds to a 

specific flow rate, therefore, only a single measurement of water surface 

elevation is needed. These weirs are traditional, easy to understand as a 

measurement tool, and accurate. 

Figure 6.2—Triangular sharp-crested weir on Medicine Bow National Forest 

measuring instream flow after water is diverted to municipal water intake. 

6.1 SHARP-CRESTED WEIRS
136

Planning and Layout of Small-Stream Diversions

The most common types of sharp-crested weirs are rectangular (figure 

6.3), triangular (figure 6.2), and trapezoidal (Cipoletti). All have walls 

(bulkheads) between which the weir blade is set vertically. The weir 

blade has a fixed opening cut in its top edge (L in figure 6.3). This 

opening is called the weir notch; its bottom edge is the weir crest. The 

weir blade projects away from the bulkhead a minimum of two measuring 

depths (H in figure 6.3). Generally, a staff gauge is placed upstream 

of the weir blade 2 to 4 feet for reading water surface elevation at the 

correct point (greater than 3 times H from the weir blade). Flow in the 

approach pool must be uniform (no rapid constriction or expansion of 

flow), tranquil (no turbulence), and no faster than 0.5 feet per second 

over the entire range of measured flow. This effectively limits the use of 

sharp-crested weirs to mildly sloping, unlined ditches.

A major disadvantage of the sharp-crested weir is that water must fall 

freely over the weir, and the downstream water surface elevation must 

be at least 2 inches below the weir crest, generally at least 6 inches 

below the upstream water surface elevation. This means a substantial 

amount of head is lost across the weir. 

Figure 6.3—Rectangular sharp-crested weir. Inset: detail of sharp-crested weir. 

The crest of a sharp-crested weir is narrow along the direction of flow and the 

falling water does not cling to the downstream edge of the blade.

HEAD WALL

STAFF GAUGE

AT 3-4 H

FROM WEIR

WEIR BLADE
137

Chapter 6—Flow Measurement

The different types of sharp-crested weirs can measure somewhat 

different flow rates. Table 6.1, at the end of the chapter, compares flow 

rates measurable by structures up to 5 feet wide. Although rectangular 

and trapezoidal weirs can be of any width, the “Water Measurement 

Manual” limits triangular weirs to a maximum width of 2.5 feet.

Where are they used? Sharp-crested weirs commonly are used at 

measuring points in unlined ditches where there is enough slope to lose 

6 inches or so over the weir. The design is standardized, but dimensions 

are designed specifically for the site and the range of measured flows. 

Sharp-crested weirs are very accurate at low flows, but they are not 

suitable for measuring large flows because they are easily submerged 

when the downstream water surface approaches the weir crest. Debris 

can be caught on the crest and sediment tends to deposit upstream 

of the weir. They do not work well in pipes or lined canals because the 

velocity of water approaching the weir must be less than 0.5 foot per 

second.

Installation. Sharp-crested weirs can be constructed of wood, 

aluminum, steel, or concrete. Metal installations are commonly 

prefabricated and can be hauled to the site on an ATV. Wood and 

concrete structures also can be prefabricated; however, this is not as 

commonly done. To be accurate, the weir must be constructed with the 

specified angles and dimensions. A common problem observed is the 

use of 2-inch boards for the crest, rather than a sharply beveled edge 

(Pearson 2002). 

Care must be taken during installation to avoid seepage under or around 

the structure. The weir must be vertical and level across the top, and 

there must be an adequate difference in upstream and downstream 

water surface elevation to allow the weir to function properly. The 

ditchbanks must be high enough to prevent the ditch from overtopping 

upstream of the weir. Downstream scour protection is needed to protect 

the ditch bed and banks from the turbulence caused by water spilling 

over the weir crest. Bank erosion and undercutting are two of the 

common modes of weir failure.
138

Planning and Layout of Small-Stream Diversions

Operation and maintenance. If the staff gauge has a water level 

recorder, little operator attention is required except to ensure that 

sediment and debris are removed from the approach pool. Accurate 

measurements require that the approach section be clean (for tranquil, 

uniform, low velocity flow), so post-flood maintenance is essential. Weir 

measurement accuracy also depends on the weir plate being plumb 

and level. For that reason, weirs are vulnerable to vandalism, and 

measurements can be put at risk by tree roots and ice that may shift the 

weir. 

What are they? Measuring flumes are shaped, open-channel flow 

sections that force flow to accelerate by converging the sidewalls, 

raising the bottom, or a combination of both. This causes the flow to 

pass through critical depth, which creates a unique water surface 

profile within the flume for each flow rate. As long as the crest is not 

backwatered, a single water-depth measurement upstream of the crest—

at a distance three times the height of water over the crest—provides the 

flow measurement. 

The most common flumes used to measure diversion flows are longthroated (also called broad-crested weirs or ramp flumes) and shortthroated or Parshall flumes. Several specialized structures, such as 

H-flumes, cutthroat flumes, Palmer-Bowles flumes, flat-bottomed 

trapezoidal flumes, and special sediment-passing flumes are used under 

special circumstances. The “Water Measurement Manual” (Bureau of 

Reclamation 2001) contains information on these specialized weirs and 

their applications.

In long-throated flumes, the approach channel floor (invert) ramps up 

to a flat sill or crest extending across the entire structure (figure 6.4). 

At the end of the sill, a vertical drop or a gradual downstream ramp 

returns flow to normal depth. Short-throated or Parshall flumes have a 

series of segments with different floor slopes and wall angles that force 

the water through critical depth (figure 6.5). Because they are complex 

and less accurate than long-throated flumes, Parshall flumes are not 

recommended for new installations except where required due to laws or 

compact agreements.

6.2 MEASURING FLUMES
139

Chapter 6—Flow Measurement

Figure 6.4—Long-throated flume. (A) drawing. (B) Salmon Falls Canal, west of 

Rogerson, ID. (C) Twin Falls main canal below Milner Dam, ID. 

B

A

C

STAFF GAUGE
140

Planning and Layout of Small-Stream Diversions

Figure 6.5—Parshall flume (A) drawing. (B) Parshall flume in an unnamed 

irrigation lateral west of Terrebonne, OR.

B

A

GAUGE

GAUGE

GAUGE
141

Chapter 6—Flow Measurement

Flumes have several advantages over sharp-crested weirs: 

1. A wide range (0.03 to over 3,000 cfs) of flows can be measured using various flume sizes.

2. For a given head drop, a flume can measure a wider range of flows 

than a sharp-crested weir. 

3. Flume head loss is less than approximately one-fourth of that required to operate a sharp-crested weir of the same control width. 

4. The gradual convergence sections encourage the passage of sediment and floating debris.

Where are they generally used? Long-throated (ramp) flumes can be 

used on both lined and unlined ditches, although in unlined ditches a 

sharp-crested weir or orifice would likely be less expensive to construct 

and install. They are less complex than short-throated flumes, can have 

customized cross sectional shapes, and are more accurate (±2 percent 

compared to ±5 percent for short-throated flumes). 

For flumes, as for weirs, approach flow should be tranquil and uniform. 

Approach velocity should be higher than for sharp-crested weirs—

between 1 and 3 feet per second. Ramp flumes are less sensitive to 

backwatering than other devices, so they might be appropriate where 

water surface elevation in the ditch varies, such as where the farmer 

puts in a ditch plug to irrigate a field. Ramp flumes also can be designed 

to fit in pipes or in ditches of various cross-section shapes, which saves 

the installer from having to reshape the ditch to accommodate the flume. 

The upstream banks must be high enough to prevent overtopping, and 

scour protection is needed downstream, especially when using shortthroated flumes. 

Accurate flow measurement requires free flow across the structure. If 

downstream backwater (in flat landscapes or where flow resistance 

increases downstream) comes close to drowning critical depth in the 

flume, two head measurements are required to quantify flow, resulting 

in significant loss of accuracy compared to free-flow measurement 

techniques. 
142

Planning and Layout of Small-Stream Diversions

Installation. Flume designs are standardized, and customized 

prefabricated units with calibration tables can be ordered commercially 

(see for example, NuWay flumes). More commonly, flumes are made to 

specified dimensions by a fabrication shop. Computer programs such as 

WinFlume can be used to calibrate long-throated flumes. However, most 

flumes can be designed quickly and more easily by an engineer for the 

specific conditions of the site: bank height, slope, and range of flows to 

measure. 

Flumes can be constructed of wood, concrete, galvanized sheet metal, 

or other materials. They can be prefabricated and hauled on an ATV, and 

small structures can even be completely constructed offsite and placed 

in one piece. Like weirs, flumes have moderate-to-high installation costs. 

They may be somewhat more expensive to construct because they 

are longer than weirs and require more material. If installation is done 

separately from other work, and an excavator is mobilized, a steel flume 

for a 3-foot ditch might cost as much as $3,000. 

One problem observed with owner-fabricated units is that structure 

dimensions may be slightly off, which reduces measurement accuracy. 

Flumes must also be level to measure flow accurately, so precision is 

important during installation. The staff gauge location also is critical to 

accuracy.

Flumes require bank and streambed protection to avoid undercutting and 

lateral erosion. They also should have collars or antiseep walls to reduce 

seepage through the banks adjacent to the structure, and ensure that as 

much as possible of the diverted flow is measured. 

Operation and maintenance. Requirements are reading and recording 

the staff gauge to keep the flow record, and clearing the approach pool 

of sediment and debris. Sediment and debris collecting in the approach 

section are common causes of inaccurate readings. Flumes should be 

checked annually to ensure they remain level. 
143

Chapter 6—Flow Measurement

What are they? A submerged orifice is an opening below the water 

surface through which water flows (see section 3, headgates). Orifices 

constructed for use as flow measuring devices are well-defined, sharpedged openings in a wall or bulkhead. For irrigation use, circular 

or rectangular orifices commonly are placed in vertical surfaces 

perpendicular to the direction of flow (figure 6.6). One type of ditch 

headgate—a sliding gate on the end of a smooth or corrugated pipe 

(ARMCO)—has been empirically calibrated as a measurement device, 

a meter gate (Cadena and Magallanez 2005). Observation wells 

or cylinders on either side of the meter gate provide upstream and 

downstream head measurement. Meter gates typically are purchased as 

separate systems from commercial suppliers who supply tables for flow 

rate determination (Bureau of Reclamation 2001).

Figure 6.6—Rectangular submerged orifice drawing.

Submerged orifices measure relatively large flows with little head loss 

(i.e., only a small drop in water surface). This allows them to conserve 

delivery head in comparison to the losses associated with flumes or 

weirs. 

6.3 SUBMERGED ORIFICES

STAFF GAUGE A

STAFF GAUGE B
144

Planning and Layout of Small-Stream Diversions

To determine the flow rate, the size and shape of the orifice and the 

change in water surface elevation across the flume must be known 

(figure 6.6). Two head measurements (upstream and downstream) are 

required. Commercial devices come with calibration tables that show 

flow for any combination of upstream and downstream water surface 

elevation. If the orifice is operating in a free flow situation (i.e., not 

submerged), then only an upstream head measurement is required. 

Where are they generally used? Orifices conserve available head 

and are useful in situations where insufficient fall is present for weir flow 

measurements. They also require less space than weirs or flumes. The 

water should be screened or fairly clean of debris since orifices are prone 

to plugging with debris. 

Installation. Installation involves excavating the ditch, constructing 

wingwalls and headwalls, setting and leveling the structure, and 

backfilling and stabilizing the installation. Verify that the orifice as installed 

reads as designed, that is, measure the flow with a different method 

and compare it with the discharge listed on the calibration table for the 

head difference. Calibrating the orifice is vital, since field conditions must 

match closely those assumed in orifice design.

Typically, stand-alone orifices are more expensive and less accurate 

than sharp-crested weirs and some long-throated flumes. Naturally, 

the expense depends on the availability of material and construction 

equipment. An orifice measuring device can be quite inexpensive where it 

is included with another system component, such as in figure 6.7, where 

it is part of the fish screen. 
145

Chapter 6—Flow Measurement

Figure 6.7—A rectangular orifice flow measurement component is designed 

into this modular vertical flat plate fish screen, designed by Pat Schille, and 

constructed at the Yakima, WA, screen shop. 

Operation and Maintenance. Orifice measurements are more timeconsuming and require somewhat more effort than weir or flume 

measurements: you have to read water surface elevation on both sides 

of the orifice, figure the difference, and then read the flow from the 

calibration table. 
146

Planning and Layout of Small-Stream Diversions

Orifices are the water measuring structures most susceptible to debris 

accumulations. They are less likely than a weir or flume to accumulate 

sediment. Accumulations of either debris or sediment upstream of the 

orifice can alter flow conditions and result in inaccurate measurements, 

so regularly clearing debris and sediment from the area is an important 

operational chore. If the orifice is completely blocked, the structure can 

overtop and even fail. 

Table 6.1 is a comparison of measurable flow ranges and head loss 

for structures approximately 4- to 5-feet wide. All structures except 

for triangular weirs can be made much larger and can measure larger 

flows. Recalibration is necessary for flow measurement in cases where 

structures vary from standard size and configuration.

Structure

Type

Rectangular Weir (contracted)2

Triangular Weir 

Cipoletti (trapezoidal) Weirs

Short-Throated Flume

(Parshall flume)

Long-Throated Flume 

(broad-crested weir)3

Submerged 

Rectangular Orifice4

Maximum 

Flow

(cfs)

33.5

4.3

33.5

85.6

64

4.38

Minimum 

Flow

(cfs)

0.12

0.5

0.13

2.22

7.6

0.49

Minimum 

Head Loss 

(ft)1

0.05

0.05

0.05

0.33

0.13

0.1

Sharp-crested weirs

Broad-crested weirs

Submerged orifices

Table 6.1—Comparison of measurable flow ranges and head loss for structures approximately 4- to 5-feet wide

1 Minimum headloss across the weir for an accurate measurement with a single upstream measurement (weirs 

and flumes).

2 Flows for sharp-crested weirs are shown for head above weir crest of 1.99 ft. Weir width, excluding wingwalls, is 

approximately 4 ft. 

3 Channel side slopes of 1.5:1, bottom width of 2.0 ft, maximum canal depth of 4.0 ft.

4 Orifice cross-sectional area of 1.0 ft2

 and head differential from 0.01 ft to 0.80 ft.
147

Chapter 7—Operations, Monitoring, and Maintenance Plan

An operations, monitoring, and maintenance (OM&M) plan should 

be prepared in conjunction with any diversion upgrade and/or permit 

renewal. The purpose of the OM&M plan is to identify clearly what 

actions are required to maintain effective and efficient operations that 

limit the diversion’s impact on the stream channel, riparian area, water 

quality, and aquatic species. The plan should address infrastructure 

requirements, routine maintenance needs, hazards, and environmental 

factors. Examples might be actions to deal with corrosive or unstable 

soils, corrosive water, storage of fuels and lubricants, the effects 

of recent fires or floods, aquatic species movement needs, winter 

shutdown, spring runoff, and summer storm adjustments. Typically, 

the engineer/designer or manufacturer of a system will provide a basic 

OM&M plan. 

Table 7.1 presents general summaries of required activities for each 

component of a diversion facility. These summaries may be useful as 

a basis for constructing your own OM&M plan, which should be geared 

specifically to the site, the installation, its recent history, and to the water 

user’s needs and interests. 

Chapter 7—Operations, Monitoring, and Maintenance Plan
148

Planning and Layout of Small-Stream Diversions

OM&M actions required

Annually

Fill conveyance system 

with water at beginning 

of season; dewater 

at end of season.

Clean out sediment 

accumulations.

Inspect for and repair 

damage from animals, 

ice, vandals, fire, flood, 

tree roots, excessive 

vegetation growth, 

and so forth.

Inspect for exposed or 

eroded banks: repair 

and reseed.

System 

Component

Water 

Conveyance to 

User (ditch, pipe, 

canal)

Daily

Adjust headgate to 

maintain desired flow 

and required freeboard 

(daily checks and 

adjustments likely 

needed in spring or 

when flows vary).

Weekly

Inspect for and repair 

damage caused by 

animals (beavers, 

ground squirrels, 

and so forth).

Inspect mechanical 

appurtenances (waste 

ways and gates) and 

repair as needed.

Monthly/Periodically

Inspect for excess 

vegetation growth; 

clear if needed.

Inspect for and 

repair damage from 

uncontrolled storm 

runoff.

Check freeboard 

during maximum water 

diversions—may be 

needed daily in spring.

Table 7.1—OM&M actions required
149

Chapter 7—Operations, Monitoring, and Maintenance Plan

Annually

Adjust and tighten 

operator bolts.

Clear out sediment 

accumulations.

Inspect for and repair 

damage from ice, 

vandals, fire, flood, tree 

roots, moss build-up, and 

so forth.

Check seal and repair as 

needed to prevent water 

from entering ditch when 

closed.

Inspect for and repair 

damage from ice, 

vandals, fire, flood, tree 

roots, moss buildup, and 

so forth.

Repair any eroded banks 

(especially in downstream 

scour pool).

System 

Component

Headgate

Diversion 

Structure

Daily

Adjust and control flow. 

Check for debris 

accumulation.

Adjust stoplog or gate 

position to maintain 

required diversion flow.

Weekly

Check for and remove 

debris and sediment 

accumulations.

Inspect for and repair 

damage caused by 

animals (beavers, ground 

squirrels, and so forth).Inspect for and remove 

sediment and debris 

accumulations.

Record changes made to 

stoplog or gate operating 

settings. 

Inspect for and repair 

damage caused by 

animals (beavers, ground 

squirrels, and so forth)

Monthly/Periodically

Inspect for and clear 

excess vegetation 

growth.

Inspect for and repair 

damage caused by 

weather.

Lubricate gate stem 

(leadascrew) semi 

annually.

Inspect for and clear 

excess vegetation 

growth.

Table 7.1—OM&M actions required (continued)

OM&M actions required
150

Planning and Layout of Small-Stream Diversions

Annually

Inspect for high velocity 

areas. The approach 

channel may have 

changed, altering how 

water enters the screen.

System 

Component

Fish Screen

Note: In many 

cases, an agency or 

organization provides 

the fish screen or 

fishway. Ensure the 

diverter and agency 

acknowledge any 

potential conflicts 

and agree on how to 

operate the diversion.

Daily

Remove floating debris 

from screen surface.

Check to ensure cleaning 

system is operating as 

needed. 

Check screen for 

damage.

Check freeboard 

during maximum water 

diversions.

Inspect bypass pipeline 

entrance to ensure it 

is free from debris and 

sediment blockage and 

has adequate flow.

Weekly

Check for fish passing 

over, through, or around 

screen; repair as needed.

Lubricate bearings and 

mechanical components 

of the screen cleaner.

Inspect for and remove 

sediment accumulations.

Inspect for and repair 

damage caused by 

animals (beavers, ground 

squirrels, and so forth).

Adjust flow through 

screen if necessary and 

ensure flow is distributed 

as evenly as possible 

across the screen.

Monthly/Periodically

Inspect for and clear 

excess vegetation 

growth.

Table 7.1—OM&M actions required (continued)

OM&M actions required
151

Chapter 7—Operations, Monitoring, and Maintenance Plan Annually Repair any erosion on entrance and exit pool banks. Inspect for and repair damage caused by ice, vegetation (tree roots, moss buildup), floods, vandals, or fire. Check device is level.

System 

Component

Fishway (upstream 

passage)

Water 

Measurement 

Devices

Daily

Inspect fishway entrance 

to ensure it is free from 

debris and sediment 

blockage.

Inspect outfall and 

measure flow rate to 

ensure sufficient flow 

depth and discharge pool 

depth are provided for 

fish passage.

Check for and remove 

debris caught in upstream 

approach reach or on 

crest of device.

Weekly

Inspect for and repair 

damage caused by 

animals (beavers, ground 

squirrels, and so forth).

Check for sediment 

accumulation in upstream 

approach reach 

(deposits will increase 

water surface elevation 

and interfere with flow 

measurement). Remove 

as needed.

Inspect for and repair 

damage caused by 

animals (beavers, 

ground squirrels).

Monthly/Periodically

Remove excess 

vegetation.

Remove excess 

vegetation.

Table 7.1—OM&M actions required (continued)

OM&M actions required

153

Glossary/Bibliography

An anchor: a heavy object buried in the streambed and chained to a log 

or other weir component to stabilize it and prevent it from floating away.

The bankfull channel is the channel width, depth, or area filled with 

water just as rising water spills onto the flood plain. Bankfull flow is often 

described as a channel-forming flow because it is a frequently occurring 

high flow that, in many channels, transports the most sediment and 

correlates with channel size (Emmett and Wolman 2001). See Forest 

Service Stream System Technology Center DVD: “Identifying Bankfull 

Stage in the Eastern and Western United States.”

For any open channel cross section, each flow rate has two depths: a 

higher depth at subcritical flow and a lower depth at faster supercritical 

flow. Critical depth is the boundary between the two. Critical depth is 

important in flow measurements because a single depth measurement 

uniquely defines water velocity. Many flow measurement structures are 

designed to force water to critical depth through a known cross sectional 

area, so that flow rate can be read off a calibration table. 

Fines include fine gravel, sand, silt, and clay. 

Head describes the energy in a mass of water. For diversion planning 

purposes, it can be thought of as the elevation of the water surface 

above a reference level, such as the channel bed, the ditch bed, the floor 

of a hydraulic structure, or the point of water use. Velocity and pressure 

are also components of head, but they can usually be neglected in 

diversion planning. 

For the purposes of diversion planning, head loss is the decrease in 

water surface elevation between two points (section 3.2). 

A structure is outflanked when water runs around it instead of over or 

through it. This may happen during a flood if the streamwater surface 

rises higher than the walls of the structure.

Piping is erosion caused by water percolating through soil (or an earthen 

dam). This type of erosion results in small tunnels inside the soil mass 

(soil pipes), which enlarge as water progressively concentrates and 

removes more soil particles.

A mixture of rocks is poorly graded when the rocks are uniform in 

size. Because the particles are all similar in size, smaller particles are 

not present to fill the spaces between them, so these mixtures have 

continuous pore spaces through which water can move relatively rapidly. 

Meaning is the same as well sorted. 

Ballast

Bankfull channel

Critical depth

Fines

Head

Head loss

Outflanked

Piping

Poorly graded

Glossary/Bibliography
154

Planning and Layout of Small-Stream Diversions

Thalweg

Unentrenched 

(channels)

Uniform (flow)

A thalweg is a line connecting the deepest points in the channel from 

upstream to downstream along the streambed (see figure 2.2).

Entrenchment refers to vertical confinement of a channel (Rosgen 

1994). Unentrenched channels have wide flood plains where floodwaters 

can spread out, slow down, and drop their sediment and debris loads. 

Unentrenched channels often meander across a relatively flat valley 

floor, and erosion on the outsides of meander bends can cause these 

channels to shift location and alignment. Streambanks are often low and 

erodible where vegetation has been removed. 

Uniform flow is straight, without expansions, contractions, or turbulence.
155

Glossary/Bibliography

Adams, S.B; Schmetterling, D.A.; Young, M.K. 2005. Instream movements by boreal toads. 

Herpatology Review 26(1): 27-33.

Adkins, G. B. 2006. Flow measurement devices. Utah Division of Water Rights. Online at <http://

waterrights.utah.gov/distinfo/measurement_devices.pdf>. Accessed 4/23/2010.

Bates, K.K. 2006. Assessment of diversion related structures within the Sawtooth National 

Recreation Area. Prepared for the Sawtooth National Recreation Area and USDA Forest 

Service. Boise, ID: U.S. Department of Agriculture, Forest Service, Intermountain Region, 

Instream Flow Group. 

Bates, K.K.; Love, M. (in preparation). Modifying culverts for fish passage. San Dimas, CA: U.S. 

Department of Agriculture, Forest Service, National Technology and Development Program. 

Bohn, C,C.; King, J.G. 2000. Stream channel responses to stream flow diversion on small streams of 

the Snake River drainage, Idaho. RMRS-RP-20. Ogden, UT: U.S. Department of Agriculture, 

Forest Service, Rocky Mountain Research Station. 

Bureau of Reclamation. 2001. Water measurement manual. 3rd edition. Washington, DC: U.S. 

Government Printing Office. Online at <http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/>. 

Accessed 4/23/2010.

Bureau of Reclamation. 2009. The WinFlume Home Page. <http://www.usbr.gov/pmts/hydraulics_lab/

winflume/>. Accessed 4/23/2010.

Cadena, F.; Magallanez, H. 2005. Analytical solution for circular gates as flow metering 

structures. J Irrigation and Drainage 131(5): 451-456.

California Department of Fish and Game. 2009. Fish passage design and implementation. Part XII of 

the California salmonid stream habitat restoration manual. Online at <http://www.dfg.ca.gov/fish/

REsources/HabitatManual.asp>. Accessed 4/23/2010.

Colyer, W. 2010. Personal communication. September 14, 2010.

Emmett, W.W.; Wolman, M.G. 2001. Effective discharge and gravel bed rivers. Earth Surface 

Processes and Landforms. 26: 1369-1380.

A

B

E

C
156

Planning and Layout of Small-Stream Diversions

Federal Interagency Stream Restoration Working Group. 2001. Stream corridor restoration: 

principles, practices, and processes. U.S. Department of Agriculture, Natural Resources 

Conservation Service National Engineering Handbook 653. Online at <http://www.nrcs.usda.

gov/technical/stream_restoration/>. Accessed 5/17/2010.

Forest Service Stream-Simulation Working Group. 2008. Stream simulation: an ecological approach 

to providing passage for aquatic organisms at road-stream crossings. San Dimas, CA: U.S. 

Department of Agriculture, Forest Service, National Technology and Development Program. 

Online at <http://www.stream.fs.fed.us/fishxing/aop_pdfs.html>. Accessed 4/23/2010.

Gale, S.B.; Zale, A.V. 2008. Effectiveness of fish screens to prevent entrainment of westslope 

cutthroat trout into irrigation canals. North American Journal of Fisheries Management. 28(5): 

1541-1553. 

Heiner, B.J. 2009. Parshall flume staff gauge location and entrance wingwall discharge 

calibration corrections. Logan, UT: Utah State University, Department of Civil and 

Environmental Engineering. Master’s Thesis. Online at <http://digitalcommons.usu.edu/

etd/480>. Accessed 3/3/10. 

Hill, R. 1999. How good is your water measurement? Logan, UT: Utah State University Cooperative 

Extension AG/BIE/WM/01. Online at <http://extension.usu.edu/files/publications/publication/

AG_BIE_WM_01.pdf>. Accessed 4/23/2010.

Moulton, M. 2010. Personal communication. Review comments transmitted via email to K. 

Clarkin 6/10/2010. 

National Oceanic and Atmosphere Administration, National Marine Fisheries Service. 2008. 

Anadromous salmonid passage facility design. Portland, OR: National Marine Fisheries 

Service, Northwest Region. 

Northcote, T.G. 1998. Migratory behavior of fish and its significance to movement through riverine fish 

passage facilities. In Fish Migration and Fish Bypasses. 1998. Jungwirth, M.; Schmutz, S.; 

Weiss, S., eds. Oxford, England: Fishing News Books, Oxford, England. 

Pearson, K.E. 2002. Irrigation water measurement. Agronomy Note #348. Bozeman, MT: 

Montana State University Extension. Online at <http://agnotes.org/AgNotes/docs/348.htm>. P

Accessed 4/23/2010.

N

M

H

G

F
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Rosgen, D. L. 1994. A classification of natural rivers. Catena. 22: 169-199.

Rosgen, D. L. 2001. The cross-vane, W-weir, and J-hook vane structures: their description, 

design and application to stream stabilization and river restoration. Fort Collins, CO: Wildland 

Hydrology Inc. Online at <http://www.wildlandhydrology.com/assets/cross-vane.pdf>. Accessed 

4/24/2010.

Schmetterling, D.A.; Adams, S.B. 2004. Summer movements within the fish community of a 

small montane stream. North American Journal of Fisheries Management 24:1163-72.

U.S. Department of Agriculture, Forest Service. 2003. Identifying bankfull stages in the eastern 

and western United States. DVD. Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station, Stream Systems Technology Center.

U.S. Department of Agriculture, Forest Service, Watershed, Fish, Wildlife, and Rare Plants Staff. [In 

preparation]. Water rights and uses site visit field guide. Washington, DC.

U.S. Department of Agriculture, Natural Resources Conservation Service. 2001. Design of rock weirs. 

Engineering Technical Note 13. Online at <ftp://ftp-fc.sc.egov.usda.gov/ID/technical/technotes/

engineering/eng_tn13.pdf>. Accessed 4/23/2010.

U.S. Department of Agriculture, Natural Resources Conservation Service. 2007a. Flow-changing 

techniques. National Engineering Handbook Part 654-Technical Supplement 14H. Online at 

<http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17817.wba>. Accessed 

12/21/10.

U.S. Department of Agriculture, Natural Resources Conservation Service. 2007b. Grade control 

structures. National Engineering Handbook Part 654-Technical Supplement 14G. Online at 

<http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17816.wba>. Accessed 

12/21/10.

Washington Department of Fish and Wildlife. [2000 draft] Fish protection screen guidelines for 

Washington State. Online at <http://wdfw.wa.gov/hab/ahg/screen51.pdf>. Accessed 4/21/2010.

Washington Department of Fish and Wildlife. [2000 draft] Fishway guidelines for Washington State. 

Online at <http://wdfw.wa.gov/hab/ahg/fishguid.pdf>. Accessed 4/23/2010. 

Witte, L. G. 2001. Still no water for the woods. Salt Lake City, UT: ALI-ABA Federal Lands Law 

Conference. Oct 19, 2001. 

R

S

U

W

Appendix A—Site Assessment Checklists

159

DIVERSION STRUCTURE SITE DATA CHECKLIST

Diversion Name: _________________________ Stream: ________________________________

Site ID:_________________________________ Tributary to: _____________________________

Prepared By: ____________________________ Date: __________________________________

Weather: _______________________________ Time: __________________________________

Location(lat/long): ________________________ Map Reference: _________________________

Water Right Owner: _______________________ Phone No.:______________________________

Owner’s Address: __________________________________________________________________

_________________________________________________________________________________

_________________________________________________________________________________

Water Right No.: ___________________________________________________________________

Total Possible Diversion Flow: ________________________________________________________

Type of Diversion: __________________________________________________________________

_________________________________________________________________________________

_________________________________________________________________________________

Diversion Condition: ________________________________________________________________

_________________________________________________________________________________

_________________________________________________________________________________

In-stream Fish Passage Issues: _______________________________________________________

_________________________________________________________________________________

_________________________________________________________________________________

Appendix A—Site Assessment Checklist
160

Planning and Layout of Small-Stream Diversions

Available Written Comments/key points for field visit

Information

Site Assessment

Design Report

Construction Drawings

O&M Plan

Watershed Plan 

TMDL Study

Grant Application 

1

 Indicate items available and check if reviewed.

41
Appendix A—Site Assessment Checklists

161

INFRASTRUCTURE OBSERVATIONS

Structure Type (describe) Present/Evaluated6 Condition Description and Photo No.

Diversion Structure

Fish ScreenFish BypassWater Measuring Device

Flow ControlOther

6 If structure is present but not evaluated = P; if structure was evaluated = E
162

Planning and Layout of Small-Stream Diversions

Problem

Sediment DepositionErosion/HeadcutsStream Bed Scour/DegradationLateral Channel InstabilityDitch FailuresAquatic Animal Passage Upstream and DownstreamOperation and MaintenanceOther:

Condition

Geology/SoilsStream TypeStructuresLand OwnershipArchaeologyVegetationAquatic and terrestrial biota

Evidence

 Potential constraint on diversion location, layout and/or design

See list of common constraints in table 2.2

See list of common problems in table 2.1

SITE CONDITIONS
Appendix A—Site Assessment Checklists

163

FLOW

Flow Condition Diverted Flow Method of Determination Stream Flow Method of Determination

Site Visit Flow

Max Diversion Flow

Stock Water Flow

High Runoff Flow7

7 Diversion designers typically use the 25-year flow as the high design flow. The recurrence interval can be higher if resource 

protection warrants.

SITE SKETCH

Include downstream and upstream survey endpoints, channel alignment, channel features (pools, sediment accumulation), diversion structure/dam, ditch/pipe entrance and alignment, fish screen, bypass, water measurement structure, cross section locations. 
164

Planning and Layout of Small-Stream Diversions

DIVERSION SITE SURVEY

This survey data form includes the minimum number of points needed for planning upgrades at a site 

with no existing fish screen or bypass channel. The form should be expanded (or data taken in a field 

book) to accommodate other points that may be important to describe your site. For a typical diversion 

site, the graphic shows the general area where each point would be taken; locations may vary for 

different types of diversions. See table 2.3 in chapter 2 for explanation of points. 

Temporary benchmark(s): Elevation________ Description:____________________________________

Longitudinal Profile Notes

Measurement Points BS FS (water depth

(thalweg) (+) HI (-) Elevation for survey point)

Beginning of Profile:

Downstream 

Downstream Cross Section

Pool Tail-out/Riffle crest

Pool Maximum Depth

Thalweg Below Dam

Dam Crest

Immediately Above Dam

Opposite Ditch 

Ditch Entrance/Headgate

Ditch Bank at Headgate, 

Right/Left

Upstream Cross Section

End of Profile (Upstream)

Ditch, 100-200 ft Down Ditch

from Headgate

Ditch Bank 100-200 ft Down

Ditch From Headgate, Right/Left
Appendix A—Site Assessment Checklists

165

Downstream Cross Section at LP _______’

Longitudinal Profile Notes

Measurement Points BS FS (water depth

(thalweg) (+) HI (-) Elevation for survey point)

Left Endpoint 

Top Left Bank

Bottom Left Bank

Left Edge of Water

Thalweg 

Right Edge of Water

Bottom Right Bank

Top Right Bank

Right Endpoint

 

Upstream Cross Section at LP _______’

Left Endpoint 

Top Left Bank

Bottom Left Bank

Left Edge of Water

Thalweg 

Right Edge of Water

Bottom Right Bank

Top Right Bank

Right Endpoint
166

Planning and Layout of Small-Stream Diversions

Other Survey Observations

Headgate Size_____________________________________________________________________

Ditch Width _______________________________________________________________________

High Water Elevations Where Measured (Distance on LP)

_________________ ________________

_________________ ________________

_________________ ________________

_________________ ________________

TYPICAL SITE PLAN WITH MINIMUM LONGITUDINAL PROFILE SURVEY POINTS
Appendix B—Automating River Diversions

167

Demand for water in and from national forests continues to increase; and 

water temperature, water quality, and in-stream and riparian habitats are 

being managed with increasing care and administrative oversight. 

The emerging need to improve management of surface-water diversions 

to maintain desired in-stream flows clearly is apparent. 

Flow management criteria in the future will not only need to specify the 

amount of water diverted under a water right, but also the amount left in 

the stream. How might these water management criteria be met? Handcontrolled ditch gates and onsite flow measurement by reading a gauge 

may be effective enough in some cases; however, traditional methods 

may not permit rapid enough response to flow changes in the river where: 

● Water is scarce. 

● Withdrawals must be coordinated with multiple users. 

● Habitat for threatened or endangered aquatic species is at risk. 

● Ditch overtopping would do environmental damage.

New irrigation systems also require flexible water delivery. In the past, 

water users typically received a constant flow rate on a predetermined 

schedule, and this was often adequate for managing their surface 

irrigation systems. However, as the variety of irrigation systems has 

increased, the need for more flexible flow management, both in 

timing and quantity, has become apparent. For example, end guns 

on center pivot systems turn on and off, and microirrigation systems 

irrigate different-sized fields on schedules based on the weather 

(evapotranspiration rates and precipitation).

A river diversion typically has several primary functions, including:

● On/off control of water.

● Flow rate control.

● Flow rate measurement.

● Volumetric measurement (Burt 2010).

Appendix B—Automating River Diversions
168

Planning and Layout of Small-Stream Diversions

Automating the functions of an irrigation turnout is becoming increasingly 

common, as the available technology improves, and as farmers’ 

management practices require additional flexibility. Remote control and 

monitoring of flow rates throughout a whole system is also possible. 

Automation does not necessarily imply complexity, as shown in figure 

B.1 (an example of a float control).

A float control maintains a constant water level upstream or downstream 

of the head gate (figure B.1). With the downstream water level at the 

pivot axis, the gate is balanced so that the moment caused by the center 

of gravity about the hinge is equal to the moment caused by the upthrust 

of the float. Any change in the water level alters this stability, causing the 

gate to rotate. The resulting increase or decrease in discharge restores 

the water level to the pivot centerline. The float control requires no power 

and little maintenance as long as the diversion is screened to keep trash 

from interfering with gate operation. 

One disadvantage of the float gate from the water user’s perspective 

is the difficulty in changing the setting or making adjustments. Also the 

flow rate can vary as the gate adjusts to maintain the desired upstream 

or downstream water level. For more information, see flap-gate design 

information from the Irrigation Training and Research Center (ITRC 

2007).

Figure B.1—Automatic float gate used to maintain constant water level on the inlet 

screen for the Hood River Canal Diversion, Hood River, OR. Only the closer gate is 

operating, and it is adjusting to keep the upstream (on left) water level the same. The 

float or ballast is the round tube at the end of the levered gate. 
Appendix B—Automating River Diversions

169

Another simple automated setup for flow monitoring might be a water 

level sensor on a flume or weir with a datalogger that is downloaded by 

hand. 

More complex automated systems improve the flexibility and 

responsiveness of diversion management with remote monitoring and 

headgate-control functions. Supervisory Control and Data Acquisition 

(SCADA) systems are used in industry to monitor and control complex 

processes for manufacturing plants, power grids, and pipelines. As wateruser demands and regulatory requirements continue to rise, irrigation 

districts and other water users have begun to deploy SCADA systems to 

better manage water withdrawals and distributions. Some systems also 

aim to make the system transparent to all users by providing real-time 

flow monitoring data via the Internet (see, for example, the Sevier River 

Water Users Association Virtual River Basin 2011). 

The costs associated with installing SCADA components will probably 

limit their application for small diversions on National Forest System 

lands for some time. However, that may no longer be true for larger 

installations. The technology is changing rapidly, and as electronic 

components come down further in cost, increase their functionality, and 

become more robust for field use, the economic feasibility of remote 

monitoring and control will increase. At a minimum, these systems are 

worth knowing about as potential future tools. 

Unlike the independent systems described above, many SCADA 

systems include data transmission to a base station computer for remote 

monitoring and/or control. Several levels of SCADA systems can be 

generally identified (Smith and Magnuson 2005):

● Monitor only (likely lowest cost).

● Monitor and manual remote control.

● Local automated control.

● Full gate or canal automation (likely highest cost).

SCADA systems for diversions
170

Planning and Layout of Small-Stream Diversions

A monitoring-only system might consist of an onsite water-level sensor 

(pressure transducer or ultrasonic water-level sensor), RTU device, 

and power source (figure B.2). Data are transmitted to the base station, 

and conversion of water level to flow information might be done by 

software provided with the sensor, by the RTU, or by the central system. 

It is increasingly common for sensors to include datalogging or RTU 

functions, and many can also transmit data to the office computer at 

set intervals. Regardless of the system components, a backup battery 

should be installed in case of power failure. This kind of system requires 

the water user to travel to the site to manipulate the ditch gate by hand.

Figure B.2—Broad-crested weir on the Twin Falls main canal, Murtaugh, ID. 

This is the main measuring device for the Twin Falls Irrigation District. It is 

remotely monitored by telemetry and is powered by solar panels. Telemetered 

data from this site is used to adjust upstream head gates to regulate flow to 

a setpoint that is monitored at this weir. A setpoint is simply the target gauge 

reading or flow that is required.

Remote Terminal Unit

A remote terminal unit 

(RTU) is the electronic 

component of a SCADA 

system—a computer—

located at the diversion 

site. RTU is a widely used, 

generic term that covers 

many different devices. 

Functions an RTU may have 

include datalogging and 

storage, communicating 

with the central office 

computer (base station), 

and controlling the various 

sensors or controllers at 

the site. They are generally 

programmed to interrogate 

the sensors or other 

instruments at the site at 

preprogrammed intervals. 

They may store that 

information until the base 

station calls to download 

it, or they may update 

the base station regularly 

automatically. Some can 

transmit settings changes 

requested by the base 

station to attached devices 

(e.g., a gate controller/

actuator). 
Appendix B—Automating River Diversions

171

A monitoring and manual remote control system would add a gate 

actuator (motor and cable system that moves the gate up and down 

and a position sensor) and controller functionality. This means the 

RTU receives information from the sensor and sends commands to the 

actuator (figure B.3). Together with the water-level sensor, this system 

allows the operator in the office to remotely open or close the gate and to 

monitor changes in water level. 

Figure B.3—Automatic gate at Twin Falls main canal, Murtaugh, ID. From left to 

right---solar panel and antenna; three boxes containing the RTU; regular screw 

type gate with the actuator, and a cover over the gate stem. The tube running 

along the back of the concrete head wall goes to a water surface level sensor 

that measures how much water is flowing through the gate.
172

Planning and Layout of Small-Stream Diversions

A local automated control system has all of the above plus an RTU 

programmed to maintain a constant flow by moving the gate up or 

down to a setpoint in response to a water level reading (figure B.4). 

The controlling water level is commonly in the ditch, but it could also 

be in the stream itself, if criteria were based on streamflow rather 

than ditchflow. This is referred to as ‘local control’ because all the 

components needed to measure and control ditchflow are onsite and 

responding to preprogrammed criteria or setpoints. Flow targets and 

adjustment criteria can be changed remotely if necessary. Data might be 

stored in the base station computer with some backup storage capacity 

onsite. 

Figure B.4—SCADA components for Middle Cub River diversion, ID. From left 

to right: the breaker panel for alternating current grid power, the flow meter local 

readout (blue), and the RTU. The RTU reads the flow from the flowmeter and 

adjusts the automated gate to maintain the flow at the programmed setpoint. 

Note the telephone: The irrigation district can call in to the RTU and check the 

flows, gate position, and make adjustments to the flow setpoint without visiting 

the site. 
Appendix B—Automating River Diversions

173

Some irrigation districts have wireless communication systems that 

enable users or ditchriders to view real-time flows throughout the system 

from their office, home, or truck (Burt et al. 2007). Webcams also are 

installed frequently to enable users to visually check the position and 

condition of the gates (e.g., trash buildup). Remote monitoring and 

control systems are customized depending on the user’s information and 

control needs. Generally irrigation SCADA systems are comprised of 

some combination of the following components, several of which may be 

housed in the RTU:

● Water level measurement sensor/flow calculation software/

datalogger.

● Motorized gate, gate actuator, gate position sensor.

● Remote computer, central system (office computer), and software 

allowing secure access to remote computer.

● Human-machine interface: user interface software that enables 

communication, control, and display of system status and 

monitoring results (figure B.5). 

● Telecommunication equipment: radio, cell phone, satellite phone, 

telephone line.

● Power supply (12 volt direct current or 110 volt alternating current).

Figure B.5—One of the monitoring and control panels for the Hood River canal 

SCADA system. This panel shows real-time pressure measurements and flows 

from three sources to the power plant. 
174

Planning and Layout of Small-Stream Diversions

Constraints for automation and SCADA systems

Communication. Transmitting data is likely to be more difficult on forest 

lands than in agricultural environments. Generally, equipment relying on 

line-of-sight (radio) cannot be used, and many wireless dead zones may 

exist. Several options are available for communications at remote sites. 

One is meteor burst communications, which is a radio propagation mode 

that exploits the ionized trails of meteors during atmospheric entry to 

establish brief communications paths between sites. This is the method 

that is used by the USDA Natural Resources Conservation Service 

(NRCS) for its remote Snowtel sites. NRCS assists water users in setting 

up and using meteor burst communications. 

Other possible methods are commercial satellite phone services, 

the geostationary operational environmental satellite (GOES) 

communications used by the U.S. Geological Survey and other 

government agencies, and frequency-hopping spread spectrum 

radios that may or may not require a frequency license and are used 

in conjunction with repeater stations. The GOES system requires 

an unobstructed view of the southern horizon. To receive data from 

GOES, a water user would need to enter into an agreement with a 

Federal agency, most likely the USDA Forest Service or USDA Natural 

Resources Conservation Service, U.S. Geological Survey, or the Bureau 

of Land Management. 

Power Supply. A power supply can be another thorny issue when no 

power lines are available. Some automatic gates (e.g., float gates) 

require no power. Others can be run from solar panels (figure B.2). 

Many remote weather sites are powered by solar panels and glass-mat 

battery combinations, which would be very applicable for many diversion 

sites. Sites requiring more power could consider fuel cells, methanol 

generators, or other types of generators. Cost of the various power 

supplies are from $1,200 for a 50-watt solar panel and two glass-mat 

batteries up to tens of thousands of dollars. Most systems should be 

able to use a solar panel and battery setup unless they are operating 

many controls or doing frequent transmitting. 
Appendix B—Automating River Diversions

175

System design and setup. Currently, turnkey SCADA systems rarely are 

available (however, see the Rubicon SCADAConnect system). Individual 

components are available but operators need to understand how to 

apply them to their specific situation, or they need to find someone 

knowledgeable enough to piece the various components together. People 

who specialize in setting up SCADA systems are called integrators 

because they combine components from different suppliers into an 

integrated monitoring/communication/power/control system. They also 

provide local support for the built system over time, which can be quite 

important.

Cost. SCADA costs (2010) vary widely, depending on the purpose, the 

approach to communication, scale, and instrumentation requirements. 

Costs depend strongly on specific site characteristics. As a hypothetical 

example, consider a remote diversion with a single gate located in a 

small valley with a good view of the southern horizon. Line of sight is 

restricted but could be maintained with two additional repeaters. The 

options are:

1. Automate the gate and set it for specific flow rate. Equipment would 

include a power supply, gate sensor, gate actuator set to maintain 

the desired flow rate, and probably a datalogger. 

2. Monitor remotely without any automation. Equipment: datalogger, 

transmitter, power supply, communication method.

3. Automate the gate with remote monitoring and manual remote 

control. In addition to equipment required for options 1 and 2, an 

RTU collects and sends data, receives commands, and makes gate 

adjustments.

Option 1: An automated (not float) gate costs between $5,000 and 

$5,500 per gate installed.

Option 2: Remote monitoring only. Dollar amounts in this example only 

include setting up and using the referenced communication method. 
176

Planning and Layout of Small-Stream Diversions

Method Equipment and Monthly Access

 Installation Cost Fee

Satellite modem $7,500 $40

GOES Satellite1,2 $4,800 $30

Meteor Burst2 $9,075

Broad spectrum Radio3 $16,175

1

 Requires a clear view of the southern horizon.

2

 Requires agreement with government agency.

3

 Includes the cost of two repeaters.

Option 3: Monitoring plus control. The broad spectrum radio is the only 

method that would approximate real time control and feedback. Some 

equipment can be used for both monitoring and automation/control. 

The cost range is approximately $19,000 to $22,000, depending on the 

number of repeaters needed. 

Option 3 is the system most irrigation companies use if they use SCADA

systems. Naturally, the cost increases as the scale increases. For 

irrigation districts that monitor and control dozens of gates with custom 

software, SCADA installation and setup can run into the hundreds of 

thousands of dollars. Complex systems like this also need people skilled 

in operating and maintaining mechanical and electronic equipment, and 

knowledgeable about the software that controls them.

SCADA technology and its application to diversion control are changing 

rapidly. Devices are coming out with more monitoring, control, and 

communication features, and costs are decreasing. In the future, 

automatic or remotely controlled flow control systems are likely to be 

more and more critical for serving off-channel water users while achieving 

the in-stream flow regimes needed to maintain riparian vegetation and 

aquatic wildlife populations.
Appendix B—Automating River Diversions

177

REFERENCES

Burt, C.; Piao, X.; Gaudi, F. 2007. SCADA information umbrellas for 

irrigation districts. In SCADA and related technologies for irrigation 

district modernization II, Proc 2007 USCID Water Management 

Conference. U.S. Committee on Irrigation and Drainage, Denver CO.

Burt, C. 2010. Irrigation district turnouts. ITRC Report R 10-002, San 

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