The Rio Grande Compact: Steven E. Vandiver started with the Colo- Its the Law! rado Division of Water Resources in 1973 as a hydrographer-in-training in Denver. He came to Alamosa as a hydrographer shortly thereafter and continued to move up through the ranks as Lead Hydrographer, Dam Safety The Adminis- tration of the Engineer, and Assistant Division Engineer. Rio Grande In 1981, Steve assumed the responsibilities of Compact the Division Engineer for Division 3, the Rio in Colorado Grande basin in Colorado. Steve, as Engi- neer Adviser for Colorado, was involved in the administration of the Rio Grande Com- pact and the Costilla Creek Compact. He was also a member of the Rio Grande Silvery Minnow Recovery Team. Steve holds a bachelors degree in civil engineering from the University of Colorado, Boulder and is a registered professional engineer.
The Administration of the the Compact and still meet her obligations to the Rio Grande Compact downstream states. Since 1939, the administration of the Rio in Colorado Grande Compact in Colorado has been an evolutionary process marked by three distinct periods. The first period from 1939-1967 was a time when Colorado officials made the decision to INTRODUCTION continue with the administration of water rights as they had during the study period of 1927 to 1936. The Rio Grande Compact requires Colorado This action worked well until 1952 when to deliver certain amounts of water annually to the Colorado under-delivered approximately 154,000 stateline according to the delivery schedules in acre-feet. The reasons for this under-delivery are Article III. On any given year this can require largely unknown, but it began a period of under- from 25 to 50 percent of the water generated in deliveries and accrued debit that continued until the Rio Grande and Conejos River basins to 1967 when that accrued debit reached approxi- arrive at the Lobatos gage just above the border mately 940,000 acre-feet. The year before, in with New Mexico. Since the diverters have the 1966, the states of Texas and New Mexico had capability of diverting and using most of the water brought an action against Colorado in the U.S. generated in both basins, it is necessary that a Supreme Court to force Colorado to comply with process be in place that enables Colorado to the provisions of the Compact. In May of 1968, ensure that her obligation is met. One can imagine the Court granted the three states and the U.S. a the turmoil that can be generated when water is stipulation for continuance of the case as long as bypassed to the stateline when there is a Colorado met her Compact obligation until she significant demand for that water in Colorado was once again in compliance. from the water rights owners on the rivers. A The second period, from 1968 to 1985, great amount of work was required by the State of Colorado administered the Compact pursuant to Colorado and the water users in the San Luis the stipulation and was forced to determine a way WRRI Valley to reach an administrative scheme that to curtail water rights in a manner that would Conference allowed Colorado to use her entitlements under allow the appropriate delivery of water to the Proceedings 1999 1 The Rio Grande Compact: Lobatos gage near the stateline. Since this PERTINENT COLORADO WATER LAW Its the Law! administrative scenario had never been attempted, the Colorado State Engineer entered a very When the State of Colorado achieved difficult time of working with the water users on statehood in 1876, her corresponding constitution both the Conejos River and the Rio Grande to included and adopted the Doctrine of Prior determine how this issue might be resolved. In Appropriation as the basis for the appropriation The Adminis- 1975, after several years of negotiated informal of the water. This was a matter of necessity due to tration of the annual operative criteria, the State Engineer the water-short characteristics of many of the Rio Grande promulgated rules and regulations for the streams in the State. It was recognized early on Compact intrastate administration of the Compact on each that because of the large numbers of competing in Colorado river and between the two rivers. In 1979, the appropriations that some judicial confirmation numerous protests to the proposed rules were would be required to allow for the orderly heard in the local District Court in an eleven-week distribution of the States water. It was also trial. The decision rendered by the Court upheld authorized by the legislature in 1883 that a State the State Engineers Compact rules but the ruling Engineer would be given the responsibility to was appealed to the Colorado Supreme Court. administer the water rights of the State. The Supreme Court decision upholding the State As early as 1883, general adjudications were Engineers rules was made in 1983. Therefore, held on the Conejos River that confirmed and from approximately 1968 to the present, the decreed water rights in relative priority based on Colorado State Engineer has directed that the the date of appropriation and the amount required Compact be administered as a two-river system to satisfy the irrigation requirements under each with each river responsible for its own delivery ditch. The first general adjudication that occurred obligation dictated by Article III. The rules also on the Rio Grande mainstem was signed on May provided that any curtailment of diversions would 1, 1896. These adjudicatory processes were come from the junior water rights, which would widely noticed and all individuals who had have otherwise been in priority on any given day completed their appropriations were allowed to of administration. During this period of litigation come forward and provide proof of their claims. over the rules, Colorado met or exceeded its The date of appropriation, the legal description of obligation each year from 1968 through 1984 the point of diversion, the flow rate of the because of the incentive provided by the U.S. appropriation, and the use to which the water Supreme Court stipulation. In fact, because of the right was to be placed was determined by the hydrologic and climatologic vagaries of the Upper court and confirmed. The court referee Rio Grande Basin, coupled with the negative investigated each claim for accuracy, ranked the consequences of noncompliance with the water rights according to the appropriation dates, stipulation, Colorado was forced to over-deliver and recommended the court decree them to ensure that she met the obligation. This very accordingly. The State Engineer, through water conservative administration resulted in a reduction commissioners, used these decrees to administer in the accrued debit of approximately 430,000 and deliver the available water to those who were acre-feet in 17 years. entitled to it. Subsequent supplemental The third and current period began in June of adjudications would include all new or existing 1985, when the Rio Grande Project in Southern claims not previously decreed and create additions New Mexico spilled and eliminated the debt of to the water rights administrative list. All water Colorado and New Mexico. This gave cause for rights in these subsequent adjudications were the three states to recommend to the U.S. junior to all previously adjudicated rights Supreme Court that the 1966 case be dismissed, regardless of their appropriation date. Therefore, which it was on December 9, 1985. Since 1985, a water right may have a very early appropriation Colorado has operated under the Compact as it date, but having failed to participate in the was written and has met or exceeded its obligation original adjudication, would end up junior to all since that time. What is required to accomplish others in the original adjudication. this administration is the topic of this paper and The following table describes the adjudication WRRI will be described in detail below. dates and the amounts decreed in each on the two Conference Proceedings 1999 2 The Rio Grande Compact: Compact streams in Colorado. The Conejos well as the State to acquire real-time data in order Its the Law! adjudications include the Los Pinos and the San to ensure better administration. Antonio rivers because they are tributaries. It is readily apparent that the vast majority of the HYDROLOGY OF THE RIO GRANDE AND water available in both systems was decreed by CONEJOS RIVER around the turn of the century. The hydrology of The Adminis- the two basins described later in the text will show The headwaters of the Rio Grande mainstem tration of the the grossly over-appropriated nature of the two and the Conejos River are ringed by the Conti- Rio Grande streams. nental Divide. This area of southwestern Colorado Compact normally receives a significant snowpack that in Colorado Rio Grande Conejos River provides the majority of the water that arrives at and tributaries and tributaries the upper index gages on the two rivers. These headwater areas are in relatively close proximity 1896: 3209 cfs 1883: 1459 cfs to the index gaging stations near Del Norte, 1903: 2501 1890: 1312 Mogote, and Ortiz. Normally, the days snowmelt 1916: 678 1914: 502 or rain event runoff arrives at the gages during the 1934: 353 1915 to present: 375 next 12 to 24 hours, depending on what location 1959: 765 in the basin one might consider. Since the 1960 to present: 140 operating reservoirs on both systems control only a fraction of the flow, the flows at the index gages Total including instream flow: are primarily a reflection of snowmelt and rainfall 9139 cfs 4104 cfs events. All these reservoirs hold relatively junior priorities and during the runoff, the reservoirs These adjudications established early on the store under those decrees on a very limited basis system of administration that has followed for when the flows at the index gages are very large. more than 100 years. Gaging stations were Therefore, during the irrigation season, the established on all streams that had become fully reservoirs bypass the inflow to them except for appropriated that allowed the water commis- the highest portion of the runoff, if at all. Three sioners to determine the amount of water that was ditches own the three irrigation reservoirs on the available for distribution. Recognition of return Rio Grande and the water from their decrees is flows and tributary inflow to the stream make the not available to any other ditches on the river. The task even more interesting. On the Rio Grande Conejos Water Conservancy District, on the other mainstem, gages were established routinely along hand, operates Platoro Reservoir and the water the course of the river to help recognize the from it is available to the member ditches. It is a changes in the flow throughout the system. commonly held belief that all the irrigation Through the years, the State Engineer has hired a reservoirs on the Rio Grande are available to all staff of hydrographers to operate and maintain the the ditches, or to store water for other purposes. gaging stations and to rate the measuring flumes This is obviously not the case and only the owners on the ditches. The State Engineer is responsible of the reservoirs can use the water available to for the distribution of water in the system to them. Since Platoro is a post-Compact reservoir, ensure the water is available at the time and place any water stored under its decree is accounted for of demand by water right owners who are in as if it had passed the Mogote gage on a monthly priority. His staff is also responsible for ensuring basis. This stored water is then subtracted when it that the ratings on the ditches are kept current to is released to ensure that the native water in the ensure the proper amount of water is delivered to basin is properly accounted for and that the index each ditch. Headgates and measuring flumes are supply and the corresponding obligation are not required by statute on each diversion and the State altered because of storage. The annual volumes of Engineer has the authority to refuse water to the flow at the index stations are therefore relatively owners who fail to maintain these structures in unaffected by the reservoirs on either of the proper order. In recent developments, most of the Compact streams except on the occasion of a very WRRI larger diversions have installed satellite- wet year when some carryover can result. Conference monitoring equipment, which allows the user as Proceedings 1999 3 The Rio Grande Compact: Its the Law! Rio Grande River near Del Norte, CO AF * 1000 Annual Calendar Year Flows Running Avg.
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Figure 1. Rio Grande near Del Norte, CO, Annual Calendar Year Flows The hourly, daily, seasonal and annual flows Peak flows on both systems are also reflective at the index stations are extremely variable. The of the large variability of the low from year to daily diurnal effect during the runoff season as year. On the Rio Grande near Del Norte gage, the well as the variability of high altitude snowmelt peak averages around 5,400 cfs and varies over can cause large changes within the day as well as the history of the record from 1,730 cfs in 1977 to from day to day. As is the situation with most 18,000 cfs in 1912. The Conejos near Mogote western streams, the seasonal and annual flows gage shows a similar pattern with peak flows are also highly variable. The past 25 years are a from 882 cfs in 1972 to 9,000 cfs in 1912 with wonderful case study on variability of the water the average around 2,000 cfs. supply for the Rio Grande Basin. On the Rio Average flows for the two rivers reflect that Grande mainstem in Colorado, we have seen the the historic mean flow is demonstrative of the fact historic low year in 1977 of 215,000 acre-feet and that neither carries large flows on the average and just a few years later saw three consecutive that the large majority of the flows occur in the annual flows of more than 1,000,000 acre-feet, a spring months of May through July. The rest of volume which has been exceeded only in seven of the year the flows are near base-flow conditions the 110 years of recorded history. Figure 1 Rio except for the runoff from the occasional rainfall Grande River near Del Norte, CO Annual event during the summer and fall. The mean flow Calendar Year Flows shows the annual for the Rio Grande near Del Norte gage is 907 variability of streamflow at the Rio Grande near cfs, for the Conejos near Mogote is 331 cfs, for Del Norte gage. This gage is the upper index gage the Los Pinos near Ortiz is 121 cfs, and for the for the Rio Grande and is used to determine the San Antonio near Ortiz is 26 cfs. Base flows on amount of water owed to the downstream states as the four rivers would be approximately 400 cfs, WRRI well as the water available for distribution in 150 cfs, 40 cfs, and 10 cfs, respectively. Conference priority to water rights owners. Proceedings 1999 4 The Rio Grande Compact: Its the Law! Rio Grande River near Del Norte, CO. CY = 1996
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Figure 2. Rio Grande near Del Norte, CO for 1996
Rio Grande River near Del Norte, CO. CY = 1997
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This variability creates a difficult and major diversions; Rio Grande challenge to the managers of the diversion systems Spreadsheets for water accounting; Compact and especially to those responsible for ensuring 10-day reporting; in Colorado that Colorado meets her Compact obligation to Natural Resources Conservation Service deliver water to the downstream states. The monthly forecasts; constantly moving target demands that the Communication protocol with National Compact be administered on a daily basis. The Weather Service; staff involved in this effort must be able to readily Closed Basin Project analyze the past, current, and future conditions of streamflows of the calendar year. Real-time data, Political Tools: calendar year flows-to-date and good historic Active water user associations; streamflow data are all required to calculate what Water conservation and water conservancy must be done to stay current with deliveries. The districts; challenge then is to use that knowledge to Continuing education programs to inform administer the priority system on both river users and public; systems while concurrently bypassing the proper Media relationship to inform public of amount of flow to the stateline to meet the significant events; required delivery for Compact purposes. It is Strong relationship between the State imperative to water right owners as well as the Engineer staff and water user community water managers to ensure that Colorado is able to utilize her full entitlement allowed under the CURRENT ADMINISTRATION Compact while meeting her obligations. As conditions change during the year, they must be Since 1968, the Rio Grande Compact has had recognized in a timely manner and adjustments a significant impact on water rights administration made to the administration of the river to in the Upper Rio Grande in Colorado. The State accomplish those two goals. Engineer has administered the Compact on a two- river system since that time. Both the Rio Grande TOOLS and the Conejos are administered independently according to their respective delivery obligations. There are a number of tools that the State of Therefore, two separate accountings and Colorado uses to administer effectively the Rio administration schemes are used for day-to-day Grande Compact. These include legal, physical administration. The following administration and political tools that are employed to determine process is used for both rivers and is linked only the actions that must take place for Colorado to by certain adjustments to the deliveries that are meet its obligation at the Lobatos gage. explained later. Article III of the Rio Grande Compact is the Legal Tools: pertinent section that describes what Doctrine of Prior Appropriation system administration of water rights is required to contemplated by the Constitution; provide the appropriate flow to the stateline to Case Law that reinforces and refines the meet Colorados annual obligation. That article Doctrine; sets the annual delivery obligation for each river Historic and current adjudication process; based upon the native water that flows past the 1969 Water Right Determination and index stations. The combination of the two WRRI Administration Act; separate delivery schedules determines Colorados Conference Proceedings 1999 6 The Rio Grande Compact: total obligation less the 10,000 acre-feet credit consumptive uses are 570,000 acre-feet on the Its the Law! provided by the Compact. The delivery schedules Rio Grande and 224,000 acre-feet on the Conejos are reflective of the inflow-outflow relationships system. These peak consumptive use amounts developed during the Rio Grande Joint occur when the annual flow is quite large and Investigation Study from 1927 to 1936. The considerably above the average flow. Figures 4 delivery schedules set in place the amount of and 5, Rio Grande Compact Delivery The Adminis- consumptive use that is allowed in each basin for Requirements Verses Annual Index Flows and tration of the given flows into that basin. The consumptive use Rio Grande Compact Delivery Requirements As Rio Grande that is allowed in each basin is reflected in their Percent of Annual Index Flows graphically Compact delivery schedules by subtracting the delivery demonstrate the delivery schedules in Article III. in Colorado obligation from the index flow. For each given They represent both the percentage of the index annual flow, there is a theoretical consumptive required as well as the numeric value of the use for each river and all additional flows must be obligation for the corresponding index supply. passed through the system. The maximum
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WRRI Conference Proceedings 1999 7 The Rio Grande
Compact: Rio Grande Compact Delivery Requirements As Percent of Annual Index Flows Its the Law!
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Deliveries to the stateline are not required to SEASONAL ADMINISTRATION adhere strictly to the Compacts delivery schedules on an annual basis. The Compact in Since 1968, Colorado has attempted several Article VI allows for the accrual of Compact different scenarios to ensure that Colorado would credits and debits. Colorado may under-deliver by meet her obligation. What has evolved over time as much as 100,000 acre-feet in any particular is a very successful routine that guides year, and may accrue up to 100,000 acre-feet of administrators through the year. It provides a annual debit over multiple years. Colorado may reasonably accurate method for meeting the also receive up to 150,000 acre-feet of annual obligation within a few percentage points, thus credit in any given year and may accrue an allowing Colorado to utilize fully her entitlements unlimited credit over multiple years. This credit and at the same time meet her obligation to the and debit accounting provision of the Compact downstream states. It requires recognizing the provides Colorado with some flexibility in indexes and deliveries from the first of the year to managing water use from year to year, and allows the present, assuming deliveries for the early the state to utilize the credit to enhance water winter months and adjusting the forecast for the supply in years when it will provide relief to a irrigation season as it progresses. After the annual shortage in the system. The only downside to index supply forecasts for both rivers are having credit water stored in Elephant Butte is established, then water rights are curtailed as is that approximately 10 percent of the water is lost necessary to ensure that the Compact delivery to evaporation each year. Current administration requirement is met. If the actual runoff and practices are to make deliveries that approximate summer thunderstorm activity changes the the obligation on an annual basis. Because of the forecasted index supply, adjustments are made to vagaries of the climate and hydrology, it is very deliveries to account for those changes. Large late WRRI difficult to forecast accurately enough during the season increases in the indexes require significant Conference runoff to exactly meet the delivery requirements. changes in administration that can cause Proceedings 1999 8 The Rio Grande Compact: considerable hardship to very senior pre-Compact thus the anticipated obligation is very low. This Its the Law! water rights. action will maximize deliveries to the stateline As described above, day-to-day during this period and will allow for lower administration of the Rio Grande Compact for curtailment during the irrigation season. The inter- and intrastate purposes involves a series of Closed Basin Project is pumped at a prudent level detailed calculations using historical, real-time, considering the limitations of winter operations The Adminis- and forecasted streamflow information at all and well production. The March 1 forecast is used tration of the seven of the Compact gages as well as at the to make some of the initial analyses for how the Rio Grande intermediate gages between them. Compact will be administered for the early part of Compact the irrigation season. The Rio Grande headwater in Colorado The upper index gages are: areas typically receive large accumulations of Rio Grande near Del Norte snow during this month and therefore it is Conejos River near Mogote normally assumed that significant changes will be Los Pinos River near Ortiz (April October) made to the projected index supply when the April San Antonio River at Ortiz (April October) forecast is received.
The lower index gages are: April 1st through October 31st Rio Grande near Lobatos Conejos near La Sauses (two stations) Diversions are normally allowed to commence around April 1 but because of the normally cold Flows at these locations are used to determine springs and low demand, Compact obligations are the total annual delivery obligation, to determine usually made without any curtailment. As soon as deliveries to date, and to establish a curtailment the April forecast is received from the Natural of water use if needed to meet the delivery Resources Conservation Service (NRCS) on or obligation of the year. The State Engineer, about the 7th of the month, the first comprehensive through the Engineer Adviser and the staff in the analysis is done to determine the projected index Division of Water Resources office in Alamosa, supply for the year. Upper index flows that have makes these calculations every 10 days when occurred through the end of March are added to diversions are being made, and monthly during the the forecast (AprilSeptember) and to average remainder of the year for both river systems. It is flows for October through December. This will critical to remember that each river is analyzed provide the first estimate of the annual index separately and that each river has its own delivery supply for each river. obligation. From that estimate of the annual index, the The general methodology for making these obligation for each river is determined using the calculations is described in the four following delivery schedules in Article III. Deliveries steps. The dates are for illustrative purposes only through the end of March are added to the normal and vary depending on the forecast and Compact (average) deliveries for November and December, status of the State of Colorado. Examples of the the anticipated Closed Basin Project deliveries 10-day analysis sheets and report are attached. and the appropriate portion of the 10,000 acre- foot credit. The sum of those deliveries, January 1st through March 31st subtracted from the projected obligation determines the amount of water needed at the Both the Rio Grande and the Conejos River stateline during the irrigation season (April diversions are curtailed 100 percent, that is, no October). Adjustments to the amount needed are diversions are allowed except for storage in pre- made for variables, which include Colorados Compact reservoirs. Any storage in post-Compact accrued credits or debits, return flows, tributary reservoirs is accounted for and subject to inflows or accretions to the rivers. Compact rules. An exception to the100 percent Once the amount to be delivered during the curtailment can occur if Colorado has a large irrigation season is determined, it is necessary to accrued credit, a spill of Elephant Butte has or determine how much of the available index supply WRRI will occur, or if drought conditions prevail and must be delivered on a daily basis to achieve the Conference Proceedings 1999 9 The Rio Grande Compact: desired delivery. This is accomplished by dividing Because the Compact is river specific in Its the Law! the amount of delivery required by the amount of Colorado, the process for determining curtailment index supply available during the irrigation percentages occurs independently for both the Rio season. This quotient then represents the Grande and the Conejos River and different percentage of the daily available index supply that curtailment percentages are applied to the two must bypass the Colorado diverters and be systems pursuant to the analysis described above. The Adminis- delivered to the stateline. Again, return flows, It is important to note this process relies heavily tration of the tributary inflows and groundwater accretions on forecasted inflows at least through the end of Rio Grande must be taken into consideration and the June. As the snowmelt runoff recedes, the summer Compact curtailment reduced accordingly or substantial thunderstorm activity or lack thereof begins to in Colorado over-deliveries can result. Weather conditions control the index supply for the remainder of the present of the greatest challenges for summer and fall seasons. The actual flows are administrators as the weather can cause not, and cannot be known until very late in the substantial changes to the index supply and the calendar year. While Colorado attempts to match forecast, adding significantly to the delivery the delivery requirement on an annual basis, over- obligation. Late summer or early fall rainfall and under-deliveries can and do result from events can have very dramatic effects on inaccuracies associated with inflow forecasts and administration and must be handled in a timely uncertainties associated with natural stream manner to prevent large under-deliveries. A study systems. These over- and under-deliveries are of delivery schedules shows that in higher years added or subtracted from the accrued debit or like 1999, the incremental amount of water that credit carried forward from previous years, and has to be delivered when an unexpected event the resulting status as of January 1 of each year is occurs can reach as high as 90 percent of the considered in the following years curtailment increased amount of water indexed. Therefore, calculations. during the entire irrigation season it is imperative The State of Colorado relies heavily on the that a continual monitoring of daily administration coordinated forecast inflows to the basin that are occurs to ensure that the forecast is indeed developed and provided by the Natural Resources tracking as was expected and that deliveries are Conservation Service in cooperation with the being made accordingly. National Weather Service. These forecasts are published monthly, typically beginning in January November 1st through December 31st and ending in May or June. Since Colorado analyzes her Compact status and considers Diversions on both the Rio Grande and the adjustments to the curtailment every 10 days, Conejos River are curtailed 100 percent if there is often a need for more up-to-date necessary to deliver water to the stateline to information, especially during periods of high complete the remaining deliveries. Reservoirs are runoff. Colorado has routine discussions with the typically allowed to go into storage on November Natural Resources Conservation Service and the 1. Consultation with the water users on both National Weather Service concerning trends and rivers can result in some diversions extending into intermediate forecasts prior to the release of November if the Compact will be met with the updated monthly forecasts. remaining deliveries. In fact, six large ditches on As previously discussed, the effect of the Rio Grande have obtained decrees to divert applying a curtailment to the Rio Grande and the water to recharge the aquifers in the San Luis Conejos River is to make a percentage of the Valley to the extent the water is not needed to water flowing past the index gages unavailable for meet the Compact obligation. Typically, by no diversions such that it can be delivered at the later than Thanksgiving, the winter weather has stateline. As curtailment information is developed made diversions of water impossible and all during the irrigation season, the calculated diversions are concluded. Closed Basin Project percentages are communicated to the appropriate deliveries are made to the river at the sustainable water commissioners, who use this data in their level necessary and in accordance with winter water rights administration. WRRI operations. Conference Proceedings 1999 10 The Rio Grande Compact: RESERVOIR STORAGE, TRANS-BASIN Compact water through the system. These gages Its the Law! DIVERSIONS, AND COMPACT also help establish return flows and tributary ACCOUNTING inflow that are available to help Colorado meet delivery requirements on both rivers. Most reservoirs within the Rio Grande Basin Depending on the actual deliveries made in Colorado were constructed prior to signing and during a 10-day period and considering what The Adminis- ratification of the Rio Grande Compact. As such, water is in transit, adjustments may be made to tration of the storage and releases by these reservoirs are not the curtailment. A monthly analysis of how the Rio Grande reflected in the Compact accounting performed by actual runoff compares to the forecast or how Compact the State of Colorado. By contrast, reservoirs rainfall events may be affecting the annual index in Colorado constructed after 1939 (post-Compact supply is also made. This continual updating and reservoirs) are subject to special Compact reevaluation provide Colorado administrators and restrictions concerning how and when they can water users the information to make informed store water and require adjustments to observed decisions on if or how adjustments to the flows at index gages during the accounting curtailment should be made. It also provides a procedures. For example, operations at Platoro process to assess the current conditions and if Reservoir, which is the largest post-Compact there have been changes from the assumptions reservoir in the Basin, affect the flows in the used to establish the forecast. Extreme drought or Conejos River at the Mogote Index Gage. flood conditions that change those assumptions Observed flows at the Mogote Gage must are recognized and the administration varies therefore be adjusted (upward when the reservoir accordingly. If normal summer and fall rainfall is storing water, and downward when it is does not occur and lower than normal flows releasing) in order to calculate accurately the result, then the curtailment may be reduced. If the Compact delivery obligation for the Conejos summer monsoon season provides vastly River. increased flows, then large increases in the Similar adjustments are made to streamflow curtailment may have to be made to remain gages affected by trans-basin diversions into the current on deliveries. The 1999 season is a perfect Rio Grande Basin. Annual storage, releases and example of how the curtailment must be increased evaporative losses by post-Compact reservoirs due to significant changes in the river hydrology and Basin inflows from trans-basin diversions are during the latter half of the year. As is very explicitly accounted for in the administration of evident to the observer, the flows in the later the Compact. summer months on the Upper Rio Grande were well above normal because of an unusual DAILY ADMINISTRATION monsoon flow. This rainfall dramatically increased the index supply on the river and caused Once the water commissioners for each river Colorado to increase the curtailment from 12 have received the curtailment percentage for the percent to more than 40 percent as the summer next period of the season, they incorporate that proceeded. The only way to compensate for the requirement into the delivery of water to ditches. increased obligation from the increased index After determining the amount of native flow at the supply was to increase the curtailment. These upper index station each morning, they apply the types of unforeseen events show that without curtailment percentage to that flow and thereby regular and routine monitoring and adjustment in establish what water has to bypass the ditches and operation, Colorado cannot expect to meet her flow to the lower index delivery points. The obligation within reasonable tolerances. The remainder of the water is distributed to the ditches vagaries in the hydrology and climate and the on their river in accordance with their relative inability of man to predict weather in advance priorities. Because of the distance involved makes the administration of the Compact a between the index gages and the ditches and dynamic and challenging process. delivery points, the delivery to them is time- One of the goals of the State of Colorado is to lagged. The intermediate gaging stations on the try to determine the curtailment percentage that WRRI rivers help the water commissioners track the can be applied throughout the irrigation season so Conference Proceedings 1999 11 The Rio Grande Compact: that the resulting effect of that curtailment is Its the Law! applied evenly across the priorities as the hydrograph rises and recedes. Large changes in the curtailment within the season can transfer the effect of the Compact and disproportionately affect the water rights in the system. This issue is The Adminis- extremely important to the water users on both tration of the rivers who decided long ago that the impact of the Rio Grande Compact should be shared as uniformly as Compact possible by the water rights that were in priority in Colorado in any given year.
REMARKS
Since 1968, the State of Colorado has worked diligently to develop a methodology that allows her to meet her Compact obligation. The ability to do so is hampered by a number of variables that are either unknown or subject to change without notice. Thus a system has been developed that recognizes and accounts for these variables. The system also is flexible enough that changes can be made to maintain deliveries that are required. The original curtailment and changes to it during the year directly affect the water supply for many water-right owners on the Conejos River and the Rio Grande. It is extremely important for Colorado to utilize fully the entitlements allowed under the Compact. Colorados entitlements provide water to over one-half of the irrigated land on the Rio Grande above Fort Quitman, Texas. That system has to be run without large reservoirs and is primarily a run-of-the-river operation. For this reason, it is critical for Colorado to analyze continuously and improve her methodology of Compact administration. Improved snowmelt runoff forecasting as well as improved weather forecasting would greatly enhance the ability of Colorado to meet her obligations while reducing its impact on water users. It is, and always will be, the variability and the unknowns of the hydrologic system that provide the challenges to administrators and users on the system.
WRRI Conference Proceedings 1999 12 The Rio Grande Compact: Its the Law!
The Adminis- tration of the Rio Grande Compact in Colorado
WRRI Conference Proceedings 1999 13 The Rio Grande Compact: Its the Law!
The Adminis- tration of the Rio Grande Compact in Colorado
WRRI Conference Proceedings 1999 14 The Rio Grande Compact: Its the Law!
The Adminis- tration of the Rio Grande Compact in Colorado
WRRI Conference Proceedings 1999 15 The Rio Grande Compact: Its the Law!
The Adminis- tration of the Rio Grande Compact in Colorado
WRRI Conference Proceedings 1999 16