GroMoPo Metadata for Ozark Plateau aquifer USGS model

To assess the effect that increased water use is having on the long-term availability of groundwater within the Ozark Plateaus aquifer system, a groundwater-flow model was developed using MODFLOW 2000 for a model area covering 7,340 square miles for parts of Arkansas, Kansas, Missouri, and Oklahoma. Vertically the model is divided into five units. From top to bottom these units of variable thickness are: the Western Interior Plains confining unit, the Springfield Plateau aquifer, the Ozark confining unit, the Ozark aquifer, and the St. Francois confining unit. Large mined zones contained within the Springfield Plateau aquifer are represented in the model as extensive voids with orders-of-magnitude larger hydraulic conductivity than the adjacent nonmined zones. Water-use data were compiled for the period 1960 to 2006, with the most complete data sets available for the period 1985 to 2006. In 2006, total water use from the Ozark aquifer for Missouri was 87 percent (8,531,520 cubic feet per day) of the total pumped from the Ozark aquifer, with Kansas at 7 percent (727,452 cubic feet per day), and Oklahoma at 6 percent (551,408 cubic feet per day); water use for Arkansas within the model area was minor. Water use in the model from the Springfield Plateau aquifer in 2005 was specified from reported and estimated values as 569,047 cubic feet per day. Calibration of the model was made against average water-level altitudes in the Ozark aquifer for the period 1980 to 1989 and against waterlevel altitudes obtained in 2006 for the Springfield Plateau and Ozark aquifers. Error in simulating water-level altitudes was largest where water-level altitude gradients were largest, particularly near large cones of depression. Groundwater flow within the model area occurs generally from the highlands of the Springfield Plateau in southwestern Missouri toward the west, with localized flow occurring towards rivers and pumping centers including the five largest pumping centers near Joplin, Missouri; Carthage, Missouri; Noel, Missouri; Pittsburg, Kansas; and Miami, Oklahoma. Hypothetical scenarios involving various increases in groundwater-pumping rates were analyzed with the calibrated groundwater-flow model to assess changes in the flow system from 2007 to the year 2057. Pumping rates were increased between 0 and 4 percent per year starting with the 2006 rates for all wells in the model. Sustained pumping at 2006 rates was feasible at the five pumping centers until 2057; however, increases in pumping resulted in dewatering the aquifer and thus pumpage increases were not sustainable in Carthage and Noel for the 1 percent per year pumpage increase and greater hypothetical scenarios, and in Joplin and Miami for the 4 percent per year pumpage increase hypothetical scenarios. Zone-budget analyses were performed to assess the groundwater flow into and out of three zones specified within the Ozark-aquifer layer of the model. The three zones represented the model part of the Ozark aquifer in Kansas (zone 1), Oklahoma (zone 2), and Missouri and Arkansas (zone 3). Groundwater pumping causes substantial reductions in water in storage and induces flow through the Ozark confining unit for all hypothetical scenarios evaluated. Net simulated flow in 2057 from Kansas (zone 1) to Missouri (zone 3) ranges from 74,044 cubic feet per day for 2006 pumping rates (hypothetical scenario 1) to 625,319 cubic feet per day for a 4 percent increase in pumping per year (hypothetical scenario 5). Pumping from wells completed in the Ozark aquifer is the largest component of flow out of zone 3 in Missouri and Arkansas, and varies between 88 to 91 percent of the total flow out of zone 3 for all of the hypothetical scenarios. The largest component of flow into Oklahoma (zone 2) comes from the overlying Ozark confining unit, which is consistently about 45 percent of the total. Flow from the release of water in storage, from general-head boundaries, and from zones 1 and 3 is considerably smaller values that range from 3 to 22 percent of the total flow into zone 2. The largest flow out of the Oklahoma part of the model occurs from pumping from wells and ranges from 52 to 69 percent of the total.

为评估取水增加对奥扎克高原含水层系统（Ozark Plateaus aquifer system）内地下水长期可利用性的影响，研究人员针对覆盖阿肯色州、堪萨斯州、密苏里州及俄克拉荷马州部分区域、总面积7340平方英里的模型区域，采用MODFLOW 2000构建了地下水流模型。该模型垂向上划分为5个单元，自顶向下依次为：西部内陆平原隔水层、斯普林菲尔德高原含水层、奥扎克隔水层、奥扎克含水层以及圣弗朗索瓦隔水层，各单元厚度均存在变化。斯普林菲尔德高原含水层内的大型开采带在模型中被表征为大范围空洞，其导水率（hydraulic conductivity）较相邻非开采带高出数个数量级。研究收集了1960年至2006年的用水数据，其中1985年至2006年的数据集最为完整。2006年，密苏里州从奥扎克含水层的总取水量占该含水层总抽水量的87%（8531520立方英尺/日），堪萨斯州占7%（727452立方英尺/日），俄克拉荷马州占6%（551408立方英尺/日）；模型覆盖范围内阿肯色州的取水量占比极小。2005年，模型中斯普林菲尔德高原含水层的取水量根据报告及估算值确定为569047立方英尺/日。模型校准采用了1980年至1989年奥扎克含水层的平均水位高程数据，以及2006年斯普林菲尔德高原含水层与奥扎克含水层的水位高程实测数据。水位高程模拟误差最大的区域出现在水位坡度较陡处，尤其是靠近大型降落漏斗（cone of depression）的区域。模型区域内的地下水流总体上由密苏里州西南部的斯普林菲尔德高原高地向西运移，同时存在局部水流向河流及开采中心，包括密苏里州乔普林、卡瑟奇、诺埃尔，堪萨斯州匹兹堡以及俄克拉荷马州迈阿密附近的五大开采中心。研究人员基于已校准的地下水流模型，分析了各类地下水抽采速率提升情景下2007年至2057年水流系统的变化情况。模型中所有井的抽采速率以2006年为基准，以每年0至4%的幅度提升。维持2006年抽采速率的情况下，五大开采中心的取水行为至2057年仍具备可行性；但提升抽采速率将导致含水层疏干，因此对于每年1%及以上的抽采增速情景，卡瑟奇与诺埃尔的抽采活动将无法持续；而对于每年4%的抽采增速情景，乔普林与迈阿密的抽采活动同样无法持续。研究人员开展了区带水量均衡分析（zone-budget analyses），以评估模型奥扎克含水层图层内三个指定区域的地下水流入与流出量。这三个区域分别为模型内堪萨斯州境内的奥扎克含水层部分（区域1）、俄克拉荷马州境内的奥扎克含水层部分（区域2），以及密苏里州与阿肯色州境内的奥扎克含水层部分（区域3）。所有评估情景中，地下水抽采均会导致储水量大幅减少，并诱导水流穿过奥扎克隔水层。2057年，从区域1（堪萨斯州）流向区域3（密苏里州与阿肯色州）的净模拟流量范围为：基准抽采情景（情景1）下的74044立方英尺/日，至每年抽采增速4%情景（情景5）下的625319立方英尺/日。密苏里州与阿肯色州境内的区域3的总流出量中，奥扎克含水层水井抽采为最主要的流量组分，在所有情景中占区域3总流出量的88%至91%。流入俄克拉荷马州境内区域2的最大流量组分来自上覆的奥扎克隔水层，其占总流入量的比例稳定维持在约45%。来自储水释放、通用水头边界以及区域1与区域3的流量占比相对较小，范围为总流入量的3%至22%。俄克拉荷马州模型区域的总流出量中，最大的组分来自水井抽采，占比范围为总流出量的52%至69%。