Selected Basin Characterization Model Parameters for the Great Basin Carbonate and Alluvial Aquifer System of Nevada, Utah, and Parts of Adjacent States

This dataset was created in support of a study focusing on ground-water resources in the Great Basin carbonate and alluvial aquifer system (GBCAAS). The GBCAAS is a complex aquifer system comprised of both unconsolidated and bedrock formations covering an area of approximately 110,000 square miles. The aquifer system is situated in the eastern portion of the Great Basin Province of the western United States. The eastern Great Basin is experiencing rapid population growth and has some of the highest per capita water use in the Nation. These factors, combined with the arid setting, have levied intensive demand upon current ground-water resources and, thus, predictions of future shortages. Because of the large regional extent of the aquifer system, rapid growth in the region, and the reliance upon ground water for urban populations, agriculture, and native habitats, the GBCAAS was selected by the U.S. Geological Survey (USGS) Water Resources program as part of the National Water Census Initiative to evaluate the Nation's ground-water availability.

These data are derived from the Basin Characterization Model (BCM). The BCM is a distributed-parameter, water-balance accounting model that is run on a monthly time step. The BCM incorporates spatially distributed parameters (monthly precipitation, monthly minimum and maximum air temperature, monthly potential evapotranspiration, soil-water storage capacity, and saturated hydraulic conductivity of bedrock and alluvium) to determine where excess water is available in a basin and whether the excess water is stored in the soil or infiltrates downward into underlying bedrock.

This dataset is composed of three raster layers. Two of the layers are outputs of the BCM model, one is an input. The layers are as follows:

1. Estimated average in-place recharge for the years 1940 to 2006 in the GBCAAS study area. In-place recharge is output from the BCM and is calculated as the annual mean amount of water that can drain from the soil zone directly into consolidated bedrock or unconsolidated deposits.

2. Estimated average runoff for the years 1940 to 2006 in the GBCAAS study area. Estimated runoff is output from the BCM and is calculated as the annual mean amount of water that runs off the mountain front or becomes streamflow.

3. Estimated saturated hydraulic conductivity (K) of bedrock and unconsolidated basin fill in the GBCAAS study area. The data are input to the BCM model as one of two temporally invariable inputs: storage capacity of soil and saturated hydraulic conductivity (Flint and Flint, 2007). The dataset was developed by applying assumed K values to geologic formations derived from 1:500,000-scale and 1:750,000-scale digital State geologic maps covering the study area. Hydraulic conductivity estimates of bedrock are uncertain because of the unknown hydraulic properties and spatial distributions of fractures, faults, fault gouge, and shallow infilling materials associated with different bedrock types and evaporative demand.

These data are output from a model and should be used with caution. Refer to the larger work citation for details about the data and adjustments made to estimated recharge and runoff in water balance calculations made for the GBCAAS study.

References cited:
Flint, A.L., and Flint, L.E., 2007, Application of the Basin Characterization Model to estimate in-place recharge and runoff potential in the Basin and Range carbonate-rock aquifer system, White Pine County, Nevada and adjacent areas in Nevada and Utah: U.S. Geological Survey Scientific Investigations Report 2007-5099, 30p.

本数据集为支撑一项针对大盆地碳酸盐岩与冲积含水层系统（Great Basin carbonate and alluvial aquifer system, GBCAAS）地下水资源的研究而编制。GBCAAS是一套复合型含水层系统，由松散沉积物与基岩地层共同构成，覆盖面积约110000平方英里。该含水层系统坐落于美国西部大盆地省的东部区域。大盆地东部地区正经历快速人口增长，且人均用水量位居全美前列。上述因素叠加区域干旱的环境背景，对现有地下水资源形成了高强度需求，进而催生了未来水资源短缺的预测。鉴于该含水层系统的大范围分布、区域内的快速发展，以及城市人口、农业与原生栖息地均依赖地下水，美国地质调查局（U.S. Geological Survey, USGS）水资源项目将GBCAAS纳入全国水资源普查倡议（National Water Census Initiative），以评估全美地下水可获取性。

本数据集源自流域表征模型（Basin Characterization Model, BCM）。BCM是一类分布式参数水均衡核算模型，以月为时间步长运行。该模型整合了多类空间分布参数：月降水量、月最低与最高气温、月潜在蒸散量、土壤储水容量，以及基岩与冲积层的饱和导水率，用于测算流域内富余水资源的分布位置，以及富余水量是储存在土壤层中还是下渗至下方基岩。

本数据集包含三个栅格图层，其中两个为BCM模型的输出结果，剩余一个为模型输入参数。各图层详情如下：
1. 1940年至2006年GBCAAS研究区的原位补给量估算平均值。原位补给量由BCM模型输出，计算方式为可直接从土壤层排泄至固结基岩或松散沉积物的年平均水量。
2. 1940年至2006年GBCAAS研究区的径流量估算平均值。径流量估算结果由BCM模型输出，计算方式为流出山地前缘或形成溪流径流的年平均水量。
3. GBCAAS研究区基岩与松散盆地沉积物的饱和导水率（K）估算值。该数据作为两类时间不变输入参数之一（另一类为土壤储水容量）输入至BCM模型（Flint与Flint, 2007）。本数据集通过将预设导水率值应用于研究区的地质地层而构建，所用地质数据源自覆盖研究区的1:500000与1:750000比例尺数字化州级地质图。基岩导水率的估算存在不确定性，这源于不同基岩类型相关的裂隙、断层、断层泥与浅层充填物的水力特性及空间分布尚不明确，同时也受蒸发需求的影响。

本数据集为模型输出结果，使用时需谨慎。如需了解本数据集详情，以及GBCAAS研究区水均衡计算中对补给量与径流量估算值的调整细节，请参阅相关研究文献。

引用文献：
Flint, A.L. 与 Flint, L.E., 2007, 流域表征模型在内华达州怀特松县及内华达与犹他州邻近区域的盆地与山脉碳酸盐岩含水层系统中估算原位补给量与径流潜力的应用：美国地质调查局科学调查报告2007-5099，共30页。