Comment on: “Economic and environmental tradeoffs from alternative water allocation policies in the South Saskatchewan River Basin” by Marian Weber and Marius Cutlac, CWRJ 39(4) 2014 Winter Issue

Introduction

The authors are critical of Alberta’s current system of prior allocation, based on the results of their model runs, but their description of the prior allocation system as they modelled it is substantially different from the prior allocation system as defined in Alberta’s Water Act, and as implemented in practice. Consequently, the model output for the prior allocation system is not realistic for Alberta’s portion of the South Saskatchewan River Basin (SSRB). The application of Water Conservation Objectives, as described in their modeling work, is not consistent with the approved SSRB Water Management Plan. Projections of future water use for irrigation in the SSRB are also not realistic.

Prior allocation system

In describing the current system, the authors state that: “During shortages, older senior licences receive priority, and must be filled before junior licences,” (410) and “senior licensees can call on all of their water before junior licensees” (411). They also state that: “The initial allocation under a share system is more equitable because water is reallocated from senior licensees with full allocation to junior licensees with none” (411). In describing their model of the system, they state that: “During a water shortage all senior licences must be completely filled before the next licence can be filled” (414). Their results then show that: “Under the prior allocation system, the low flow scenario results in the irrigation sector receiving 99% of the water due to seniority and size of the licences. Municipalities receive only 1% of the allocated water” and “Calgary under the prior allocation scenario…only has one licence of vintage 1895 that can be satisfied” (416). If these descriptions were completely accurate and comprehensive, and if the modelled results were realistic, concern over the prior allocation system would be understandable.

However, Alberta’s prior allocation system and its application are widely misunderstood. Section 30(2) of Alberta’s Water Act states that:

A licensee or traditional agriculture user diverting water pursuant to a licence or registration that has a numerically lower priority number is entitled to divert the whole allocation of water specified under the licence or registration before a licensee or traditional agriculture user has any right to divert water pursuant to a licence or registration that has a numerically higher priority number. (Alberta 1996)

This is consistent with the authors’ description of the system, and many people apparently assume that it is a complete description. However, it only partially explains prior allocation, and the principle which underlies the next section of the Water Act, 31(1), is vital to a correct understanding. It reads:

When a licensee’s or traditional agriculture user’s works is not of sufficient capacity to carry the diversion of water to which the licensee or traditional agriculture user is entitled under the terms and conditions of the licence or registration, the licensee’s or traditional agriculture user’s right to divert water under licence or registration is limited to the volume and rate of water that the works is capable of carrying.

As the authors (Weber and Cutlac) correctly note, water licences specify both an annual diversion volume and an instantaneous diversion rate. The instantaneous diversion rate is typically based on the design capacity of the diversion works, and it is the instantaneous diversion rate, rather than the annual volume, which normally governs the application of priority among licensees. In other words, although a licensee may be entitled to a large volume of water, and although they are technically entitled to receive all of it before any junior licensee receives any water, they are only entitled to divert the portion of the flow each day which is specified as their licenced rate of diversion, and the remaining flow is available for other more junior licensees to divert, subject to their licence conditions, whether upstream or downstream of the senior licensee’s point of diversion. For most large licences, it would take months of diversion at the licensed rate to divert the full volume, and it would be pointless for junior licensees to wait until senior allocations were filled before they could begin diverting.

For example, the Bow River Irrigation District (BRID) holds multiple water licences, with a total allocation volume of 450,000 acre feet (555,000 dam³) from the Bow River at Carseland. Of this, 380,000 acre feet (469,000 dam³) has relatively senior priorities of 1908 to 1953, while 70,000 acre feet (86,000 dam³) has a fairly junior 1992 priority. A separate licence, which is held by Alberta Environment and Sustainable Resource Development (AESRD), governs the rate of diversion. The diversion licence allows 34 cubic metres per second (cms) diversion with a 1908 priority, 7.4 cms diversion with a 1953 priority and 9.6 cms diversion with a 1992 priority, for a total maximum rate of 51.0 cms, which is the design capacity of the diversion works. The BRID is not entitled to receive all 380,000 acre feet of its senior allocation before a junior licensee gets any water. It is entitled to divert somewhere between 34 cms and 51 cms (2938 dam³ to 4406 dam³ per day), if licensees with more senior priority do not require that flow, and if all other conditions of the licences are being met. Any flow above that rate is available for diversion by licensees with more junior priorities, subject to their licence conditions, regardless of the fact that the BRID has not diverted its full senior allocation volume.

If there is insufficient flow any day for any licensee to divert at their licensed rate, they have the option of making a priority call, by informing AESRD that they need more water. AESRD than determines which licensee(s) need to temporarily reduce or cease diversion, in order to satisfy the more senior licensees’ needs. This occurs far less frequently than many critics of prior allocation assume to be the case, and it is common in even the driest years to have enough flow in the larger rivers in the SSRB to supply the needs of all licensees through the spring and early summer runoff. Since the BRID’s junior licence was issued in 1996, diversion to fill it has never been suspended due to a priority call by a senior licensee, although there have been times when diversion has been not permitted due to licence conditions regarding instream flow conditions. In addition, although the BRID’s most senior licence is still junior to the licences of the other two irrigation districts on the Bow River, it has never made a priority call which would deprive any junior licensees of diversion in order to fill its senior licence. Model results that show minimal water going to junior licensees are not reflecting reality.

Another critical misinterpretation of the prior allocation system is evidenced by the authors’ low-flow prior allocation result that gives only 1% of allocated water to municipalities, including Calgary, as they apparently assume that Calgary and other upstream municipalities are not allowed to divert any water that will be required for senior licences or inter-provincial apportionment flows downstream. In fact, because municipal use is largely non-consumptive, water allocated under junior licences can still normally be diverted, since most of it is returned to the rivers as treated wastewater. This water is then available for reuse by senior licensees downstream, or it passes into Saskatchewan as part of the required inter-provincial apportionment flow. The two largest irrigation diversions on the Bow River, for the BRID at Carseland and the Eastern Irrigation District at Bassano, are both downstream of the return flow from Calgary’s wastewater treatment plants, and it is both legal and logical for Calgary to use the water first. The other two relatively large cities in the southern portion of the SSRB, Lethbridge and Medicine Hat, are downstream of the major irrigation diversions, but there is always more than enough water for municipal use flowing past them in order to meet the terms of the inter-provincial apportionment agreement, and there is no reason to prohibit them from using that water before returning it to the rivers. The authors allow for such municipal use in their full trading model, but apparently do not in their prior allocation model.

Aside from the apparent misinterpretation of the prior allocation system, the limitations of the Aquarius model, which runs on a monthly time step and allocates water on a monthly basis, are likely to diminish the accuracy of the output. Water supply and demand are highly variable on a daily basis, and even a weekly time step is coarse when modelling water management in the SSRB. In addition, the monthly irrigation diversion distribution which was modelled, “15, 22, 30, 20, 10 and 3% of the annual allocation from April to September” (413), is inconsistent with normal patterns of irrigation diversion in Alberta. For the 6-year period from 1999 to 2004, which was typical, the monthly irrigation diversion pattern to eight of the largest districts combined, representing more than 95% of the total diversion to irrigation districts, was 5, 15, 21, 25, 17, 12 and 5% of the total annual diversion from April to October. In 2001, the year against which the model was calibrated for low flow, this pattern was 5, 16, 24, 23, 16, 10, 5 and 3% from April to November (Alberta Agriculture and Rural Development 2014).

Water conservation objectives

The authors state that “WCOs [water conservation objectives] for the Bow, Oldman and Lower South Saskatchewan Basins were generally established at 45% of long-term natural flow” (411). The SSRB Water Management Plan recommended WCOs for these sub-basins that “are either 45% of the natural rate of flow, or the existing instream objective increased by 10%, whichever is the greater at any point of time” (Alberta Environment 2006). The WCOs are not 45% of long-term natural flow; they are 45% of the natural rate of flow each day. The only water licences that are subject to these WCOs are those that have been approved for applications made after 1 May 2005. Since these sub-basins were closed to new applications in 2007, very few junior licences are subject to WCOs. The SSRB Water Management Plan also recommended that all existing licences and licences subject to renewal should retain their original conditions for instream objectives, and that new licences stemming from applications received prior to 1 May 2005 should be given conditions for instream objectives that existed on 1 May 2005 (Alberta Environment 2006). Modeling results should have been based on existing licence conditions for instream objectives rather than WCOs, except for recent junior licences that are subject to the WCOs.

Future demand for irrigation water

A final point of interest is whether increasing demands for water for irrigation, which the authors project, are realistic. Their opening sentence includes: “demands for water continue to rise due to expanding municipal and irrigation needs…” (409). Later, in referring to a report by AMEC, they state that “by 2030, irrigated water use is expected to increase by more than 50% over 2005 levels (AMEC 2009, 411).” The AMEC report actually stated that:

By 2030, water use could increase from the current 1,981,000 dam³ to about 3,040,000 dam³, an increase of 53%. This magnitude of increase would occur if irrigation districts were to implement, under their existing licence allocations, the maximum level of expansion modelled in this study. (AMEC 2009, v, emphasis added)

Jumping from “could…if” to “is expected to” is a large leap, but it is prudent to consider whether this is likely. The maximum level of expansion modelled by AMEC equalled a 25% increase in the total irrigation district area, which was projected to potentially occur over 25 years. From 2009 to 2013, the area within irrigation districts assessed for irrigation increased by 1.6%, which is consistent with the rate of irrigation expansion in recent years, but well below the rate corresponding to AMEC’s maximum expansion projection. The trends in water use are of much greater interest. Because of high variability in annual diversion due to variations in weather, Alberta’s irrigation districts have utilized 10-year rolling averages to show trends in diversion. The 10-year rolling average diversion for all irrigation districts combined peaked in 1992 at 2,408,000 dam³. By 2005, it had decreased to 2,186,000 dam³, and in 2013 it dropped to 1,632,000 dam³. At the same time, the 10-year rolling average for the area actually being irrigated increased from 1,045,000 acres in 1992 to 1,205,000 acres in 2005 and to 1,215,000 acres in 2013 (Alberta Agriculture and Rural Development 2014). This decrease in diversion is so large that an examination of the corresponding precipitation records is worthwhile. Growing season (15 April to 15 October) rainfall records from 1970 through the present are available for Lethbridge, Brooks and Bow Island, which are located such that they are collectively representative of the primary irrigated region. The average growing season rainfall for these three locations is 259 mm for the period of record. The 10-year average rainfall was 248 mm in 1992, 235 mm in 2005, and 286 mm in 2013. Although increased rainfall tends to decrease diversion, the substantial decrease in diversion is primarily attributable to improved irrigation efficiencies. In the Alberta Irrigation Projects Association’s Conservation, Efficiency, and Productivity Plan, which was endorsed by all of the irrigation districts, one of the key targets is that “on a ten-year rolling average, the irrigation districts will keep diversions at or below the year 2005 reference benchmark of 2.186 billion m³ per year” (Alberta Irrigation Projects Association 2010, 26). Irrigation districts have been expanding the irrigated area using water saved through improved application and delivery efficiencies, while still reducing their diversions, and this trend should continue. In any given year, water demand could be high due to drought conditions, but the evidence does not support predictions of large increases in irrigation diversions in the future.