Tumalo Irrigation District

How Water Moves Through TID’s Current Hybrid System

Diversion (top of system)

• Water is captured at the highest elevation
• This elevation is what drives both pressure (pipe) and flow (ditch)
• System needs a minimum of 120 CFS to run correctly at a 70% delivery rate

The Piped system is configured to use elevation at the top of the system to produce consistent delivery pressure

• Water enters the pipeline first
• Elevation drop creates usable pressure
• Users in this zone get:
  • On-demand delivery (in most cases)
  • More consistent flow
  • Minimal conveyance loss

 Operational reality:
The pipe system captures the most efficient portion of the system hydraulics first

Remaining water transitions to ditch system

• Water not used (or routed around pipe zones) continues downstream
• Enters open ditch network
• Begins to lose volume through:
  • Seepage
  • Operational spill
  • Transit inefficiencies

Ditch system distributes remaining supply

• Delivery depends on:
  • Remaining flow
  • Gate settings
  • Physical condition of canals

 Operational reality:
Lower system is working with reduced and less controllable supply

• More variability
• More dependent on carry water
• More losses before delivery
• Surface delivery only

Where the Confusion Comes From

How the piped portion and the ditch portion physically affect each other because they are connected to the same water supply and elevation system.

The piped and ditch systems are hydraulically connected. What happens in the upper (piped) system directly affects how water arrives, behaves, and is available in the lower (ditch) system.

Operational Challenges in This System

1) Front-End Efficiency vs. Back-End Supply

• Piping reduces losses upstream
• But also reduces incidental return flows that historically fed lower ditches

Result:

• Lower system may see:
  • Less “carry” water
  • Sharper shortages during peak demand

2) Perception of Priority

• Piped users often experience:
  • Less visible shortage
• Ditch users experience:
  • Gaps in delivery
  • Delivery delays- velocity of water- re-wetting of ditches, and vegetation

 Result:

• Strong perception that pipe users are being favored, even when allocation policy is unchanged

3) Hydraulic Control Mismatch

• Pipe system = controlled, pressurized, measurable
• Ditch system = variable, manual, loss-prone

 Result:

• Two fundamentally different service levels inside one district

4) Timing Conflicts

• Pipe users may draw water continuously
• Ditch users rely on remaining water availability

 Result:

• Continuous upstream demand can flatten or delay downstream delivery.

5) Reduced Operational Flexibility

• Open ditch systems historically relied on:
  • Spill
  • Seepage
  • Reuse flows
• Piping removes much of that “flex”

 Result:

• System becomes more efficient but less forgiving

6) Peak Demand Amplification

• During hot periods:
  • Pipe users increase demand (sprinklers are running longer)
  • Ditch users need more water to receive their allocation

 Result:

• System stress increases disproportionately at the lower end

7) Measurement Gap Between Systems

• Pipe system:
  • Often metered or measurable
• Ditch system:
  • Often estimated

 Result:

• Hard to demonstrate equity across the two systems

8) Infrastructure Transition Effects

• As piping increases:
  • Flow patterns change
  • Historic delivery assumptions no longer hold

 Result:

• Lower system may feel like it is getting “left behind” during transition phases

Key Operational Reality

A hybrid system does not behave like a single system—it behaves like two different delivery systems connected in series, where the upstream system directly affects the performance of the downstream system.

The upper system is driven by pressure and efficiency. The lower system is driven by remaining supply and timing.

As we increase piping, we improve efficiency, but we also change how water arrives at the lower end.”

Managing this system is not just about allocation—it’s about balancing two fundamentally different delivery methods in real time.

 In a gravity-pressurized piped system, water delivery is more controlled and efficient than open ditch systems, but equity is still influenced by elevation, system design, and real-time demand on the network.

A gravity-pressurized pipe system does not create water. It preserves the water that would otherwise be lost in open conveyance and allows that water to be used for the open ditches.

Equity in an open ditch system must be actively managed within physical limits that do not distribute water uniformly.

Sincerely,

Chris Schull

District Manager

 

This operational reality is not new — it has been part of the Tumalo system for over 100 years. Modern drought conditions, changing snowpack timing, and increasing environmental constraints have simply made the variability more visible and harder to manage.

1. Tumalo Creek is not a stable river system

Tumalo Creek is driven by:

• Cascades Snowpack
• Rapid spring runoff
• Temperature swings

That means:

• A warm weather event can create strong flows very quickly
• A cold snap can abruptly reduce runoff
• Daily (diurnal) fluctuations can be severe during spring melt
• The creek can appear healthy one day and critically low the next 

2. Tumalo creek has a short “good window of water”

The pattern is generally:

Time Period

Typical Condition

April–June

Strong snowmelt runoff

Late June–July

Rapid decline begins

August–September

Base-flow dominated system

Fall/Winter

Very low natural live flow

This is a classic Central Oregon east-slope Cascade hydrograph:

• Strong spring peak
• Sharp recession curve
• Small late-season base flow

• Base flows around ~75 CFS
• Peak spring runoff around ~250 CFS
•  Higher flows are temporary. Once snowmelt ends, flows fall quickly.

3. The creek naturally drops to relatively small late-season flows

• Tumalo Creek is not a reservoir-fed stable supply
• There are no major regulating controls on the creek itself
• Water arrives when snow melts
• When melt ends, the system shrinks rapidly
• The creek is fundamentally different from heavily regulated reservoir systems.

4. TID’s diversion has always depended on timing and supplementation

 TID relies on:

• Live flow from Tumalo Creek
• Supplemental stored water from Crescent Lake
• Smaller Deschutes River supplies through the Bend Feed system

Federal and district documents describe the operating model clearly:

• Early irrigation season = 90% of the water from Tumalo Creek
• Later season = increasing reliance to 90% Crescent Lake storage

The major challenge is that Crescent supplementation has a travel lag of roughly five days.

So, when Tumalo Creek suddenly crashes:

• TID cannot instantly replace that water
• The system experiences operational instability
• Rolling outages and rebalancing become necessary

That has been true long before recent drought years.

5. Historically, the creek can become operationally stressed very fast

• Spring runoff can produce substantial flows
• But irrigation season often coincides with rapidly declining hydrographs
• Diversions plus declining natural runoff can reduce downstream flows dramatically
• The lower creek historically experienced severe dewatering conditions during irrigation season before modernization efforts.
• This is one reason modernization became such a major basin priority:

• Open canal seepage losses are enormous
• Conveyance inefficiency amplified shortages
• Conserved water programs became necessary to protect instream flows

6. The “live flow” narrative people often expect is not hydrologically realistic

A common public perception is:

“The creek should just continuously provide enough water.”  that has never really been the reality.

The actual reality is:

• Tumalo Creek behaves more like a fast-reacting mountain runoff system
• Flow conditions are highly weather-dependent
• There are dramatic seasonal declines
• Daily fluctuations can be severe
• Stable delivery historically required supplemental storage and operational balancing

Even in years with decent snowpack, timing matters:

• A rapid warm-up can create an early runoff peak
• Snowpack can disappear quickly
• Late-season live flow is inadequate

7. Why this matters operationally for TID

This explains why TID operations involve:

• Rotation discussions
• Balancing between pipe and open systems
• Storage supplementation
• Canal modernization
• Conserved water programs
• Operational rationing during runoff transitions

The system was originally built in an era assuming:

• Large seepage losses
• Less regulation
• Smaller demands
• Different environmental expectations

Modern operations now must simultaneously balance:

• Senior irrigation rights
• ESA/HCP requirements
• Instream protections
• Infrastructure limitations
• Highly variable snowmelt hydrology

• Short-duration spring abundance
• Rapid seasonal decline
• Significant day-to-day fluctuation
• Small late-season base flows
• Dependence on supplemental storage to stabilize deliveries