Water Management

Explore the problems and solutions associated with water management in riparian areas by clicking through the slides using the slide-navigation buttons () below.

The Problem

Historic or Natural Flows
The diagram below shows how a river like the Jocko River looked prior to irrigiaton withdrawls. The stream can handle fifty-year and one-hundred-year floods without the channel becoming destabil-ized and without excessive erosion.

Reduced Flows due to Irrigation Diversions
Reduced flows can cause the channel capacity (the amount of water the stream can carry) to be reduced. This can also result in a reduction in the width of the floodplain. A smaller channel will not be able to handle larger flood flows without increasing erosion and destablizing the channel.

Reduced Flows

Water diversions can significantly alter a river’s ecology in a number of ways. Amongst the most pronounced are that you end up with (see the illustration above):

• a smaller river, (stream width)
• a narrower floodplain, and (width of floodplain)
• and an incised channel (elevation of water height).

Irrigation canals, drainage ditches, and water-impoundment features (e.g., ponds) are common throughout the lower mainstem Jocko River floodplain. The construction of these artificial features often results in localized changes in floodplain hydrology and leads to an increase in fish entrainment (fish getting trapped in canals), spread of noxious and non-native plant species, and poor habitat for other aquatic species. Management and restoration plans for protected properties will prescribe techniques to remove or modify existing water diversions and/or impoundments as an initial step to restore floodplain hydrology.

Irrigation withdrawals can also cause channel sinuosity (how much a river winds or meanders) to decrease because channels become destabilized from carrying an increased sediment load, while the ability to transport that load has decreased. If sinuosity decreases, the slope of the stream channel increases, which increases the stream's energy and the damage done by the stream during floods.

Irrigation withdrawals can cause water temperatures to increase and this can seriously impact fish like bull trout and cutthroat that need cold water. Other impacts, like land clearing and grazing practices in the floodplain, can also impact water temperature.

Many riparian trees and shrubs require depositional surfaces where their tiny seeds can germinate without competition from other plants. Reduced flows caused by irrigation withdrawals can reduce the number of depositional features, thereby reducing the numbers of tree and shrub stands that become established over a period of several years.

Effects of drought years may be more pronounced due to irrigation withdrawals; this can cause higher mortality in young trees whose roots have not yet reached their maximum depth. It can also result in loss of wetlands.

Other impacts from irrigation practices include fish entrapment in unscreened diversions, unstable diversion points, and water quality problems associated with the irrigation return flows.

Irrigation diversions can also prevent migratory forms of bull trout and westslope cutthroat trout from moving upstream into spawning habitats.

The Solutions

Practice Water Conservation

Practice Water Conservation
Evaluate the efficiency of the total irrigation system
from the pump or diversion to return flow or tailwater.
Upgrade irrigation equipment to improve delivery and
application efficiency where feasible.

Schedule irrigation according to crop needs, soil water
depletion, and water availability, accounting for precip-itation. Apply only enough irrigation water to fill the effective crop root zone. In short, do not over water.

Time irrigations to individual crop needs to eliminate
unnecessary applications.

Monitor soil moisture by the feel method, tensiometers, resistance blocks, or other acceptable methods before and after each irrigation.

These measures not only save fish and rivers, they can save a farm or ranch by lowering water and energy costs.

Improve Diversion Structures

Improve Diversion Structures
Irrigation diversions can cause channel problems. For example, there is a diversion on the Jocko River where the annual maintenance narrows the channel. The river responds by down-cutting and degrading the stream bed. As a result, the diversion point has to be moved upstream each year to capture water. This has gone on for years, and the current diversion point is now some 700 feet upstream from the original site. An improved design would eliminate this problem.

Other diversions are barriers to fish movement, blocking bull trout and other migratory fish from their historic spawning areas. Fish ladders can solve this problem.

Still other diversions entrap fish, which is a constant drain on the fishery resource. Fish screens on diversions can remedy this problem.

Improve Management of Return Flows

Improve Management of Return Flows
Irrigation can cause water quality problems from return flows. Return flows are defined as the water that returns to a stream or groundwater after being diverted and used for irrigation. They include tail water from farms and irrigation water that seeps past the root zone of plants. Sometimes, irrigation diversions, especially private diversions, do not have control structures associated with them, and at times (depending on flow) they divert more water than is used. This results in excess or return flows that flow back into the stream, often causing water quality problems by increasing the temperature of the stream (return flows are warm) and dumping fine sediment in the stream. Both temperature increases and silt can damage native trout populations.

Adding control structures to diversions and managing irrigation systems better can eliminate or minimize return flows. Creating wetlands to trap sediment can also help to remedy return-flow problems.

Establish Ecologically Based Instream Flows

Establish Ecologically Based Instream Flows
The term "instream flow" refers to water left in a stream to maintain or improve the way the stream functions and to protect or restore fish and wildlife habitat. In contrast to out-of-stream uses, instream flows do not require diversion, rather the water stays in the stream, which has not always been the case. In the past entire sections of streams were dewatered (all the water was taken) during certain times of the year because the legal framework did not consider fish and wildlife a beneficial use of the water.

Instream flows or flow levels should be set to maintain critical habitat, to achieve a channel maintenance flow (the flow that maintains the channel shape and completes instream sediment transport). Instream flows should also incorporate higher-magnitude ecological flows—riparian maintenance and valley maintenance flows—which tend to occur when natural water supply is available. Because of their importance in reshaping floodplain topography and the distribution of floodplain sediments, the goals should be to maintain these flows in all years when there is enough natural water available.

The Benefits

Productivity

Increased Forage
Healthy riparian areas are more productive since abundant water, shelter, and forage translate into more fish and wildlife and better production for livestock producers.

For example, the graph at left shows how a well-managed riparian area produced three times the forage of a degraded floodplain. Forage is important, but so is cover and water and all three increase dramatically under good management.

Less Destructive Floods

Less Damage
Meandering streams with healthy riparian areas can reduce flood damage. A well-vegetated floodplain slows flood waters and better enables it to absorb water. This reduces stream power and stream damage during floods. A straightened channel that has been overgrazed is a recipe for serious flood damage.

More Water

More Water When We Need It
We can't change how much rain and snow falls, but we can affect how much stays to water riparian vegetation, livestock, and wildlife, and how much flows in streams for fish.

Flooding is one way streams bank water. When a stream with healthy riparian vegetation overtops its banks, the water saturates the floodplain and raises the water table. Then in late summer, fall, and winter, when stream flows are naturally at their lowest, that groundwater flows back into the stream.

Poorly managed riparian areas can cause runoff to occur over a shorter time period and produce higher peak flows. That means less retention time for water to soak into the floodplain, which means less groundwater flowing back into the stream during late summer, fall, and winter when fish, wildlife, and people need it most.

Fish and Wildlife

Fish and Wildlife
One of the greatest benefits of healthy riparian areas is a diverse and vibrant wildlife community and healthy native fishery. Riparian areas are crucial to fish and wildlife. It is estimated, for example, that approximately 80% of our wildlife species—everything from birds to mammals—depend on riparian areas for all or part of their lifecycle. The more a riparian area is degraded, the fewer resources there are for wildlife (food, cover, nesting and denning places, travel corridors, etc.) and the greater the chance that some species will disappear from an area.

More Stable Channels

More Stable Channels with Natural Shapes and Sizes
Riparian vegetation reduces the horsepower of a stream by slowing water down through friction. A three-inch-deep rootmat resists erosion up to 20,000 times better than bare-soil streambanks. Deep-rooted grasses, forbs, brush, and trees stabilize stream banks and play a major role in defining channel shape and size (lower left).

Well-vegetated streams tend to be narrow and deeper than streams with degraded riparian zones. Without roots to hold things together, the cohesive nature of streambanks breaks down, and the stream becomes wide and shallow (lower right).