Silver Springs 1000 year Capture Zone

1000-year Capture Zones represent the distance and direction water particles in the aquifer travel in a 1000-year period before reaching a spring head. The boundaries of the geographic area that contributes groundwater to the Silver Springs spring group are dynamic and can be influenced by changing climatic conditions and by anthropogenic conditions, such as groundwater withdrawals. Groundwater within the spring recharge basin (springshed) potentially emerges as discharge from the Silver Springs spring group. The USGS MODFLOW numerical code was the basis for a regional groundwater flow model encompassing north-central Florida. This model was used to simulate the groundwater flow conditions as influenced by groundwater withdrawals that occurred in 1999. The results of the 1999 simulation were then applied to the USGS MODPATH particle-tracking code. This code allows for the determination (mapping) of the origin of groundwater contributing to a specific area of interest within the model by using the reverse particle tracking method. This method traces the flowpaths of a prescribed number of water particles from their points of discharge backward to the original point of origin or to a location determined by the estimated time of travel. In this case, the model grid cell that encompasses the Silver Springs spring group is the particle point of discharge. Further documentation of this methodology is provided in the following SJRWMD special publication: http://www.sjrwmd.com SJ2007-SP4.pdf. The delineated 1000-year capture zone represent the estimated geographic extent of areas within which it would take groundwater 1000 years to travel to the discharge point at the Silver Springs spring group. The capture zone delineations are influenced by the hydrogeologic characteristics of the Surficial aquifer system (SAS) and the Floridan aquifer system (FAS) present within these areas. Horizontal groundwater flow in the Upper Floridan aquifer is, in general, the dominating factor that determines the extent of the capture zone boundaries. Note: The 1000-year capture zone encompasses nearly all of the Silver Springs recharge basin. The 1000-year capture zone in combination with an interpretation of groundwater flow direction within the upper Floridan aquifer is used to delineate the springshed boundary for the Silver Springs spring group.千年捕获区（1000-year Capture Zones）指含水层中的水颗粒在抵达泉眼前，于1000年时间内运移的距离与方向。为银泉群补给地下水的地理区域边界属于动态边界，会受到气候变化以及地下水抽取等人为活动条件的影响。泉补给盆地（泉域，springshed）内的地下水，最终可通过银泉群以径流形式排泄。美国地质调查局（USGS）开发的MODFLOW数值模型代码，是覆盖佛罗里达州中北部区域的地下水流模拟模型的基础。该模型被用于模拟1999年受地下水抽取活动影响的地下水流状态。随后，1999年模拟的结果被应用于USGS开发的MODPATH粒子追踪代码。该代码可通过反向粒子追踪法，确定模型内特定关注区域的补给地下水的来源位置并完成映射。该方法从预设数量的水颗粒的排泄点出发，反向追踪其运移路径，直至其最初的补给原点，或是抵达由估算运移时间所确定的位置。在本研究中，覆盖银泉群的模型网格单元即作为水颗粒的排泄点。本方法的进一步详细说明可参阅以下SJRWMD专项出版物：http://www.sjrwmd.com SJ2007-SP4.pdf。本次划定的千年捕获区，代表了地下水需要耗时1000年方能运移至银泉群排泄点的预估地理范围。捕获区的划定范围，受区域内表层含水层系统（Surficial aquifer system, SAS）与佛罗里达含水层系统（Floridan aquifer system, FAS）的水文地质特征影响。总体而言，上佛罗里达含水层中的水平地下水流，是决定捕获区边界范围的主导因素。注：本次划定的千年捕获区几乎覆盖了银泉补给盆地的全部范围。结合千年捕获区与上佛罗里达含水层内地下水流向的解译结果，可划定银泉群的泉域边界。