GroMoPo Metadata for SW Kansas GMD3 KGS model

Ground-water levels have been declining during the last few decades in the Ogallala-High Plains aquifer (HPA) in western Kansas, including within Southwest Kansas Groundwater Management District No. 3 (GMD3). The water-level declines have decreased ground-water discharge to the Arkansas and Cimarron rivers, thereby causing decreasing streamflow. One of the Kansas Water Plan (KWP) objectives is to "Reduce water-level declines rates within the Ogallala aquifer and implement enhanced water management in targeted areas." An associated goal of the KWP is to "Conserve and extend the life of the HPA." As a part of planning and management activities, the Kansas Water Office (under a cooperative agreement with the U.S. Bureau of Reclamation) and GMD3 contracted with the Kansas Geological Survey (KGS) to develop a computer model of the HPA in the GMD3 area to further characterize the hydrologic system and water availability. The model will provide more information on water in storage and allow projection of likely aquifer responses to possible future conditions and management scenarios (KWP, Upper Arkansas River Basin High Priority Issue, Management of the HPA). The KGS constructed a numerical model for a rectangular area of 100 by 150 miles that enclosed GMD3 and extended approximately 6 miles to the north, east, south (into Oklahoma), and west (into Colorado) of the GMD3 boundaries. The active cells included the paleovalley of the Arkansas River in Hamilton and western Kearny counties. The KGS model utilizes MODFLOW, a widely used software program for modeling ground-water flow and stream- aquifer interactions developed by the U.S. Geological Survey. The KWO formed a Technical Advisory Committee to oversee the project, which included staff of the KWO, GMD3, KDA- DWR, and a consulting firm retained by KDA-DWR to provide technical review. The main focus of the project was the development of a calibrated transient model that simulated ground-water flow and stream-aquifer interactions during the period 1947-2007. Predevelopment conditions were simulated for 1944-1946. The model included 12,083 active model cells (each a mile square), involved one layer, and simulated ground-water flow in the HPA and associated alluvial aquifers. Six recharge zones were used and the types of recharge included that from precipitation, enhancement of precipitation recharge in irrigated land, and return recharge below fields irrigated with ground-water and river water diverted from the Arkansas River. The precipitation applied to each cell varied depending on the distribution for each year across the model area. Ground-water pumpage from the HPA for Kansas during 1990-2007 was based on reported water-use records, and for earlier years was estimated from regression equations based on a de-trended ratio of water use/authorized quantity versus precipitation and the Palmer drought severity index for 1990-2007. Similar approaches were applied to estimating pumpage in the Colorado and Oklahoma portions of the model, although the procedures varied because the data and data access for pumping records are not as readily available as those for Kansas. The pumpage rate from the HPA increased from 78,000 acre-ft/yr for predevelopment to a maximum of 2,708,000 acre-ft/yr in 1991 and was 1,844,000 acre-ft/yr for 2007 in the modeled area. The percentage of irrigation return recharge was calculated for each year in Kansas counties based on data for changes in irrigation type and applied to adjacent counties in Colorado and Oklahoma. Results from the calibrated model indicated that the long-term recharge from areal precipitation averaged over the model area was 0.41 in/yr during 1946-2007. Stream-aquifer interactions were simulated for the Arkansas and Cimarron rivers and Crooked Creek. Hydraulic conductivity (K) and specific yield (Sy) were estimated using lithologic data from about 15,000 well logs examined by the KGS PST+ (practical saturated thickness) program. In order to account for the impact of declining water levels on the calculation of K and Sy during the transient period, the calibrated model was broken into six step models: 1) predevelopment, 2) predevelopment to 1966, 3) 1967 to 1976, 4) 1977 to 1986, 5) 1987 to 1996 and 6) 1997 to 2007. In each step model, K and Sy were dynamically updated using the observed water levels for the corresponding time period. During model calibration, the K and Sy values were adjusted by matching streamflows and observed water levels during each step to simulated values. A recharge function with different parameters for each of the six recharge zones was also incorporated into the calibration. The parameter estimation program PEST was employed to optimize parameters during the calibration process. The model indicates that ground-water pumping has caused substantial decreases in aquifer storage. The storage decline rate started to increase in the 1950s, accelerated in the 1960s to mid-1970s, and then approximately leveled from the late 1970s to 2007, although it varied substantially each year depending on pumping. The accumulated decline in ground-water storage simulated for the entire model area for 1947-2007 is 66,409,000 acre-ft, which comprises 29.3% of the simulated predevelopment storage. The storage decreases have been accompanied by a decrease in streamflow out of the model. Water-level declines in the HPA have resulted in the "capture" of ground water that otherwise would have discharged to streams; without this capture, the aquifer storage loss would have been approximately 12% greater than simulated. The total storage volumes simulated for the HPA only within the GMD3 area for predevelopment and the end of 2007 are 193,454,000 and 133,622,000, respectively, giving a storage decline of 59,832,000 acre-ft, which is 30.9% of the predevelopment value. The total storage volumes computed for the GMD3 area from measured water levels are 191,216,000 and 133,726,000 acre-ft for predevelopment and 2007, respectively. These values give a storage decrease of 57,490,000 acre-ft, which is 30.1% of the predevelopment volume. The storage volumes from the model and estimated from observations for the GMD3 area differ by only 1.2% and 0.1% for predevelopment and 2007 conditions. The average water-level decline simulated for all the model cells within the GMD3 area is 69.89 ft in comparison with 67.01 ft for the difference between contoured water-level surfaces based on observations in the predevelopment period to 2007. The calibrated model will be used to simulate ground-water flow and stream-aquifer interactions for future conditions involving continuation and changes in pumping, and different climatic conditions as selected by the KWO and GMD3. A separate report that presents and discusses the results of these scenarios will be prepared.

过去数十年间，堪萨斯州西部奥加拉拉-高平原含水层（HPA）的地下水位持续下降，其中包括西南堪萨斯州地下水管理区第3区（GMD3）境内。地下水位下降导致流向阿肯色河和锡马龙河的地下水排放量减少，从而引起河流径流的减少。堪萨斯州水资源计划（KWP）的一个目标是为“降低奥加拉拉含水层的水位下降速率，并在目标区域实施改进的水资源管理。”KWP的另一个相关目标是“保护和延长HPA的使用寿命。”作为规划和管理工作的一部分，堪萨斯州水资源办公室（与美国垦务局合作）与GMD3签订了合同，委托堪萨斯州地质调查局（KGS）开发GMD3区域HPA的计算机模型，以进一步描述水文系统和水资源状况。该模型将提供有关储存水资源的更多信息，并允许预测含水层对可能的未来条件和管理局面的响应（KWP，上阿肯色河流域高优先级问题，HPA的管理）。KGS为包含GMD3并延伸至GMD3边界北、东、南（进入俄克拉荷马州）和西（进入科罗拉多州）约6英里的100乘150英里矩形区域构建了一个数值模型。活跃的单元格包括哈密尔顿和凯尔尼县西部阿肯色河的古河谷。KGS模型使用MODFLOW，这是美国地质调查局开发的一种广泛用于模拟地下水流动和河流-含水层相互作用的软件程序。KWO组建了一个技术顾问委员会来监督该项目，该委员会包括KWO、GMD3、KDA-DWR的员工，以及由KDA-DWR聘请的咨询公司，以提供技术审查。该项目的重点是开发一个校准的瞬态模型，模拟1947-2007年期间的地下水流动和河流-含水层相互作用。对1944-1946年的开发前条件进行了模拟。该模型包括12,083个活跃的模型单元格（每个为一英里见方），涉及一个层，并模拟了HPA及其相关冲积含水层的地下水流动。使用了六个补给区，补给类型包括降水、灌溉土地上降水补给增强，以及地下水灌溉和从阿肯色河引水的农田的回补补给。每个单元格应用的降水根据模型区域的每年分布而变化。1990-2007年堪萨斯州从HPA的地下水抽水量基于报告的水使用记录，而对于早些年份，则是根据去趋势的水使用/授权量与降水量以及1990-2007年帕尔默干旱严重指数的回归方程进行估算。对于模型中科罗拉多州和俄克拉荷马州的抽水量估算，采用了类似的方法，尽管由于抽水记录的数据和数据获取不如堪萨斯州那么容易，因此程序有所不同。HPA从开发前到1991年的最大抽水量为2,708,000英亩英尺/年，2007年为1,844,000英亩英尺/年。根据灌溉类型的变化和应用于相邻科罗拉多州和俄克拉荷马州的数据，为堪萨斯州的每个年份计算了灌溉回补补给百分比。校准模型的结果表明，1946-2007年期间，模型区域的多年平均降水补给为0.41英寸/年。模拟了阿肯色河、锡马龙河和扭曲溪的河流-含水层相互作用。使用KGS PST+（实用饱和厚度）程序检查的大约15,000个井的岩性数据估计了水力传导率（K）和特定产量（Sy）。为了考虑下降水位对瞬态期间K和Sy计算的影响，校准模型被划分为六个步骤模型：1）开发前，2）开发前至1966年，3）1967至1976年，4）1977至1986年，5）1987至1996年，6）1997至2007年。在每个步骤模型中，使用对应时间段观察到的水位动态更新K和Sy值。在校准过程中，通过将每个步骤的河流流量和观察到的水位与模拟值匹配来调整K和Sy值。校准中还纳入了具有每个六个补给区不同参数的补给函数。参数估计程序PEST被用于校准过程中的参数优化。该模型表明，地下水抽水导致了含水层储存的显著减少。储存下降速率始于20世纪50年代，在20世纪60年代至70年代中期加速，然后从20世纪70年代末至2007年大致保持稳定，尽管每年的变化幅度很大，这取决于抽水。1947-2007年模拟的整个模型区域的累计地下水储存下降为66,409,000英亩英尺，占模拟的开发前储存的29.3%。储存减少伴随着模型流出量的减少。HPA的水位下降导致原本会排入河流的地下水被“捕获”；如果没有这种捕获，含水层储存损失将比模拟的大约多12%。仅就GMD3区域而言，模拟的HPA在开发前和2007年末的总储存量分别为193,454,000和133,622,000英亩英尺，储存下降量为59,832,000英亩英尺，占开发前价值的30.9%。根据测量的水位计算出的GMD3区域的总量分别为191,216,000和133,726,000英亩英尺，对于开发前和2007年。这些值给出了57,490,000英亩英尺的储存减少量，占开发前体积的30.1%。模型和从观测中估计的GMD3区域的储存量在开发前和2007年的条件下仅相差1.2%和0.1%。GMD3区域内所有模型单元格的平均水位下降模拟值为69.89英尺，而根据1947年至2007年观测的水位表面绘制的等高线之间的差异为67.01英尺。校准模型将被用于模拟涉及抽水持续和变化以及KWO和GMD3选择的不同的气候条件下的未来条件下的地下水流动和河流-含水层相互作用。将准备一份单独的报告，以展示和讨论这些情景的结果。