Hydrogeological entities - Mayotte

The hydrogeological entity is a part of the geological space, aquifer or non-aquifer, corresponding to a physical system characterised in terms of its state and hydrogeological characteristics. The hydrogeological entity must be understood in a systemic sense and corresponds to a division of the geological space carried out at a given stage of knowledge, in particular for deep systems. The constitution of hydrogeological entities comes from the knowledge at a given date of the underground environment (geological map, geological section, geological log, structural scheme and piezometric map). Hydrogeological entities can be multipart. Hydrogeological entities cover the entire territory ensuring a horizontal and vertical relationship of entities in accordance with the principle of completeness. A hydrogeological entity is a part of the geological space: - delimited to a certain scale (level of use) - related to a type of geological formation (theme) - defined by its aquifer potentials (nature) - characterized by a type of porosity (middle) - characterized by the presence or not of a tablecloth, which can be free, captive or free and captive (state) They have been defined according to rules developed within the framework of a common national methodology and validated by a national steering committee under the responsibility of the ministry in charge of the environment. A hydrogeological entity will be represented by its orthogonal projection to the ground. The reference scale is 1/50 000th, i.e. the scale of the national geological repository. Each entity has a code that is assigned by the BRGM (Order of 26 July 2010, SNDE). According to Sandre, dictionary of the SAQ hydrogeological repository version 2.2水文地质实体（hydrogeological entity）属于地质空间的一部分，可分为含水层（aquifer）与非含水层（non-aquifer）两类，是一类以自身状态及水文地质特征为表征的物理系统。 需从系统层面理解水文地质实体，其对应于特定认知阶段下对地质空间的划分，针对深部地质系统尤为如此。 水文地质实体的划定依据特定时期对地下环境的认知成果，包括地质图（geological map）、地质剖面（geological section）、地质测井（geological log）、构造纲要图（structural scheme）以及水压图（piezometric map）。 水文地质实体可具有多组分结构。 水文地质实体覆盖全域，依据完整性原则（completeness principle）确保实体间的水平与垂向关联。 水文地质实体作为地质空间的一部分，需满足以下界定要求： - 按特定尺度（应用层级）划定边界 - 关联某一类地质建造（主题类别） - 以其含水层潜能（本质属性）作为定义依据 - 以特定类型的孔隙介质为表征特征 - 以是否存在隔水覆盖层为判定依据，该覆盖层可使含水层呈现无压、承压或兼具无压与承压三种状态 此类实体的划定遵循统一国家方法论框架下制定的规则，并经由负责环境事务的部委牵头的国家指导委员会验证通过。 水文地质实体以其在地面的正交投影（orthogonal projection）进行表征，参考比例尺为1/50000，即国家地质数据库的标准比例尺。 每个实体均配有由法国地质矿业研究局（Bureau de Recherches Géologiques et Minières，BRGM）赋予的专属编码（依据2010年7月26日政令，SNDE标准）。 本内容依据Sandre发布的《SAQ水文地质数据库词典》2.2版整理。