Water Resource Planning Considerations for Irrigated Short Rotation Intensive Culture Projects

Mark Madison, P.E. CH2M HILL, Portland, OR

Greg Brubaker, P.E., CH2M HILL, Gainesville, FL

Implementing a large-scale short rotation intensive culture (SRIC) project requires a significant quantity of water. In order for the project to be successful and profitable, the right mixture of water resources must be identified and acquired. Careful planning is essential.

How Much Water?

For the purposes of discussion, we have estimated the water demands of a generic largescale SRIC project in the eastern United States. Using generalized water uptake rates for poplars, sweet gums, and sycamores, we have estimated peak-month irrigation demand and the annual water usage. The quantities shown in Figure 1 provide a rough indication of the amount of water that is needed for an SRIC project, based on 1.33 inches per week peak month water use at 90 percent efficiency and 40 inches per year irrigation requirement. In actuality, it would vary according to the types of trees planted and an assortment of site specific factors such as soil moisture, groundwater levels, and climatic conditions. Nevertheless, these estimates give an idea of what is meant by "significant quantities." For a 1,000-acre plantation, for example, approximately 5 million gallons per day (mad) would be needed. For the year, that plantation would need about 1 billion gallons. Five thousand acres would need 26 mad, which is equivalent ta the daily usage of a city with a population of 200,000.

Potlatch Corporation's hybrid poplar SRIC plantation in the desert near Boardman, Oregon, provides another example of the kind of water demand that can be encountered. The plantation is planned for 22,000 acres, about half of which are currently planted. The total projected water demand for the plantation is over 200 mad. The rate is high because of the hot, dry climate, with 10 inches of rain annually and a long growing season, but the production rates from this area are among the highest in the country. Depending on its location and other factors, the associated water demand of an SRIC project can range from impressive to astonishing.

Water Use Trends

Figure 1: Large-Scale SRIC Water Requirement Estimates

Irrigated SRIC plantations represent a relatively new phenomenon in agriculture that has developed in the last decade. In the east, many forest products companies are determining the feasibility of developing SRIC plantations ranging in size from 1,000 to 10,000 acres. In the west, companies such as Potlatch, James River, MacMillan Bloedel, and Boise Cascade have already implemented large-scale irrigated SRIC projects. Water demands for SRIC projects will have a significant impact on water resources in the given area. Even without additional water use by SRIC projects, the water withdrawals and consumptive use of agriculture are higher than any other sector, as illustrated in Figure 2. The thermo/electric power sector used comparable volumes, but returned most of what it took; whereas irrigated agriculture consumed a high percentage of what it took—via evapotranspiration. In 1990 all sectors consumed approximately 105 million acre-feet of water. Irrigated agriculture accounted for 81 percent of that. Clearly, irrigated agriculture is a substantial water user.

Current and projected trends point to increased competition for water resources. This competition has been at the forefront in the western states, but is beginning to arise in the eastern states as well. Irrigated agriculture or silviculture are increasingly facing a tug of war with other interests for the limited supply of water available. Other interests include public and domestic users, industry, environmentalists, and regulators.

For example, Tampa Bay and north Florida are contending for control of the Suwannee River water supply. Tampa Bay wants to pipe water from north Florida to meet its water demands because of dwindling local sources. Also in Florida, environmentalists are attempting to reduce agricultural uses of water to provide more water to the Everglades. Another example of the current trend is the battle that the states of Georgia, Florida, and South Carolina are having about over-pumping of the Floridan aquifer, which is causing salt intrusion along the coast. Similarly, concern about mill wastewater discharges is increasing.

The public's concern about environmental issues is heightened, but its concern about agricultural needs is relatively flat. Urban industrial demands are increasing in certain areas of the country, especially in the southeast, in Florida, South Carolina, and Virginia. Moreover, regulatory

limitations on surface and groundwater withdrawals have become stricter. In some states, for example, the regulatory agencies require permits for the consumptive use of water. In Florida or South Carolina and in most western states, an SRIC project would need such a permit.

Planning is Critical

Because of the large water requirements, multiplication of contending water users, and tighter regulatory constraints, a comprehensive water resources management plan is critical to the long-term success of any SRIC project. The planning should be done for full-scale operations, not just for the prototype or demonstration project. Full-scale planning activities help to identify pitfalls early in the process. A long-term perspective also helps the participants to identify the least cost mixture of water supply alternatives. In general, development of a comprehensive water resources management plan is done in three steps:

1. Determine current and future irrigation demands.
2. Appraise all possible sources of water to meet the estimated demands.
3. Select the most economic approach for satisfying the projected demands.

While straightforward in concept, the planning process may become complex in practice. Depending on the size and nature of a particular project, several detailed investigations and studies could be required to develop a viable plan.

An important element of the planning process is the collection of information. This includes stream flows, meteorological data, well capacities, water quality data, types of soils, and topography. Important decisions will be made on the basis of this information. The water demands of the project must be projected and consumptive use permitting constraints identified. Also, the project should be examined to see how the water demand will vary throughout the year, during the irrigation season, and as the trees mature. Average day and maximum day demands should be projected.

After the prevailing circumstances and the projected water demand characteristics have been identified, then the search for water supply sources can begin. This analysis should include consideration of all potential sources, how available they are, the timing of their availability, and how their capacities will vary throughout the year. How will the supply vary diurnally and seasonally? Is the water quality compatible with the proposed crops and soil types? The long-term reliability of each viable source should be determined. The investigation of water resources will probably entail careful review of the water rights permitting involved. On many projects in the western United States, water rights are an important component of the project.

When the sources have been reviewed, the different ways to regulate their flows can be analyzed. The required storage capacities need to be determined based on the locations, quantities, and occurrences of the various water supplies. Will surface or subsurface storage be required to meet irrigation needs? Typically, if groundwater is the main irrigation source, then additional storage is not required because the aquifer serves as a storage component. When required, surface storage reservoirs are normally adequate for most projects. If land is not available for surface storage facilities, or it is cost-prohibitive, alternative storage strategies, such as aquifer storage recovery (ASR) could be considered. ASR is a water management technology in which water is stored underground in a suitable aquifer through a well during times when the water is available and recovered from the same well when needed. Three principal criteria that govern ASR applicability are as follows:

• Variability in the water supply that does not match demand.
• A minimum scale of development exists, below which ASR may not be cost-effective. The development costs for the first well can be considerable. Subsequent wells can usually be brought on at a lower cost. As a preliminary guide, water supply and demand should be such that a minimum of 1 mad ASR recovery capacity should represent a useful addition to assist in meeting peak or emergency system demands. For most SRIC systems, this requirement is normally achieved.
• A storage zone that meets hydrogeologic, hydraulic, geochemical, water quality, and regulatory criteria must exist at the site.

As part of the comprehensive water resources management plan, it is important to identify the transmission system components needed and the best routes for the pipeline to the potential SRIC site.

Economic considerations are, of course, paramount in such enterprises. Typically, it is worthwhile to perform a least cost analysis that looks at various combinations of the alternatives. This should include present worth and annual cost estimates. The analysis should address anticipated capital costs (i.e., planning, permitting, design, and construction) and operating expenses for each alternative. Within this analysis, an evaluation of the benefits that will result from the implementation of each alternative should be conducted. Also, while conducting the financial analysis, project phasing should be considered with respect to annual cash flow limits for the project. Appropriate phasing can be an important factor in determining the economic viability of the project.

Additionally, the planning effort should address operations and maintenance requirements and establish the level of redundancy that is acceptable, which will significantly affect the costs associated with the project. Reasonable and sound operating budgets should be formulated, and energy and water efficient irrigation systems should be considered to make it a cost-effective project. Recently, CH2M HILL designed an automated drip irrigation system to precisely deliver filtered, chlorinated, and fertilized water to the root zones of 12 million trees at the Potlatch Corporation poplar plantation in Oregon. The plantation draws water from the Columbia River and delivers it through nearly 500 miles of main lines, 19,000 miles of drip irrigation tubing, and 24 million drip emitters. The pumping systems will cost over $1 million per year to operate. Maximizing the efficiency of water and energy use was crucial to controlling production costs and making the project feasible.

Alternative Irrigation Water Sources

An essential element of the planning process will be determining whether the native groundwater and surface water sources available will be adequate for the project. If they are not, or they are not affordable, then it is worthwhile to consider alternative sources. The types of sources available will presumably be different for each location. Some common alternative sources are:

• Mill effluent
• Domestic wastewater and biosolids
• Stormwater runoff and irrigation return flows
• Food processing wastewater
• Other industrial wastewaters

Pulp and paper mills produce approximately 4.2 billion gallons per day of effluent in the United States. Only 0.1 percent of that is currently land applied—and reuse is done at only nine mills in the nation. This yet-to-be-exploited water source could be very valuable to an SRIC project. Moreover, the pulp and paper industry will probably be under pressure from environmental groups to increase their reuse percentage to reduce waste loads to receiving streams.

If a city is close to the project site, then it would be an oversight not to consider application of reuse water or biosolids from domestic wastewater treatment plants. Stormwater runoff from cities, industrial areas, and irrigation return flows could be other potential sources. A site with well drained sands will not generate much runoff, but in some states, particularly in Florida, large irrigation projects are required to have stormwater management systems for pollution abatement. If it is already necessary to construct such a system, then it may be feasible to take advantage of the collected runoff as an irrigation source. Food processing wastewater and other industrial wastewaters in the vicinity should not be overlooked as potential sources.

Water quantity will be the factor that initiates the search for alternative sources, but water quality may be the factor that determines their suitability. Example water quality values for effluents from kraft mills, secondary treatment plants, and beverage distillation facilities are summarized in Table 1. The values for kraft mills are typical of those found in the southeastern United States. The values for secondary treatment plants are from EPA guidance documents. The values for the beverage distillation facility are taken from a CH2M HILL project performed several years ago. The groundwater quality standards for Florida are shown for comparison.

Biochemical oxygen demand (BOD) and total suspended solids (TSS) concentrations are similar for kraft mill effluent and domestic secondary treatment plant effluent. These values are acceptable for irrigation. Most food processing effluents, however, require additional treatment to reduce the high BOD and TSS concentrations. It is difficult to apply food processing effluents without installation of special filtration systems.

Mill effluent is low in nutrients, so it must be supplemented with nutrient applications. In contrast, secondary treatment effluent is an excellent source of nitrogen and phosphorus. At 20 milligrams per liter (mg/L) nitrogen, it provides about 167 pounds of nitrogen per million gallons (approximately 3 acre feet). At 10 mg/L phosphorus, it provides about 85 pounds per million gallons. The rates of application need to be controlled so that groundwater standards are not violated. This is more likely to be critical on very sandy soils with low water holding capacity. Most food processing effluents provide too much nitrogen, phosphorus, and potassium, and must be treated or diluted.

For mill effluent, the significant parameters to examine are total dissolved solids, sodium, chloride, and color. Compared with the groundwater quality standards, these parameters are typically two to three times higher. That does not mean that mill effluent cannot be used for SRIC irrigation, but it does indicate that the long-term plan must address operational modifications to protect groundwater and surface water quality in the area. Very little information is available to help establish appropriate application rates for long-term salt load management. Pilot projects are recommended to establish loading rates, leaching requirements, and dilution needs. Metals concentrations need to be looked at to see if they might limit the amount of water that can be applied to the crop. For most soils, however, they do not present a problem.

A summary of the benefits and challenges of our four examples of alternative water resources are summarized in Table 2. These include mill effluent, domestic wastewater treatment plant effluent, stormwater runoff, and food processing effluent. Some of the techniques that have been employed to deal with lower quality irrigation water include:

• Multiple, staged filtration systems
• Control valve manifolds for automated irrigation, and frequent flushing of all drip tubes
• Micro sprinklers to distribute high solids wastewater

Time domain reflectometry (TDR) or other automated technologies for soil moisture monitoring

• Modifying the irrigation cycle to maximize root zone depth
• Water source blending for water quality control

Alternative Water Source Partnerships

Several good reasons present themselves for a forest products company to establish a partnership with a wastewater generator. Foremost is the possible acquisition of a free, unrestricted water source. Additionally, the wastewater generator may be willing to help defray the costs of the irrigation system infrastructure, because it has been saved the cost of purchasing land for a water reuse application program or additional treatment to meet stream standards. Depending on the nutrient concentrations of the wastewater, fertilizer expenses and operations and maintenance costs could be reduced for the project. The forest products company may also be able to secure a hardwood source through forward contracting with a wastewater generator that has a reuse system and grows trees.

Wastewater generators will be interested in such a partnership because it will help them reduce their wastewater disposal costs. Not only will it reduce their land purchase costs, but it will also establish technical assistance from the forest products company and secure a market for the wood.

A recent present worth evaluation of disposal options for a municipal wastewater treatment plant (WWTP) in southeastern United States serves as an example of how the costs that wastewater generators face may render them especially receptive to discussions about implementing water reuse projects with forest products companies. In this instance, it was going to be necessary for the WWTP to upgrade to incorporate advanced wastewater treatment (AWT) or somehow eliminate its current effluent discharges to the river in order to meet more stringent permitting conditions. CH2M HILL analyzed a variety of options including AWT, wetlands treatment, public-access-level reuse, and land application using an SRIC hardwood tree plantation. The AWT and SRIC costs are illustrated for comparison in Figure 3. The graph shows that the estimated present worth cost for AWT was $46.7 million, whereas the present worth cost for a 1,800-acre SRIC project was $30.7 million. If land salvage costs are considered, the SRIC project cost is reduced to $25.2 million. One of the advantages of the SRIC project is that revenue can be produced in 6 to 7 years to help reduce the overall present worth cost of the option. The AWT had capital costs similar to those of the SRIC, but much higher annual operations and maintenance costs and zero revenue generating potential.

Summary

Given the increasing competition for water resources, it is probable that an SRIC project will need to obtain water from multiple sources to meet its irrigation needs. Adopting a "big picture" planning approach will help to ensure the development of a reliable, least cost system. If available, mill effluent and municipal wastewater can be excellent water sources. Water quality usually becomes an issue when using alternative water sources instead of native groundwater or surface water sources, but by employing the appropriate techniques and technological advances in irrigation and monitoring equipment, it is possible to protect the environment and cultivate trees profitably. We encourage forest products companies to investigate partnering opportunities with wastewater generators. Both parties are apt to benefit significantly by the association.

File posted on March 17, 1998; Date Modified: February 21, 1999