请帮忙分析一下这句话的句子成分

The water table is the underground boundary below which all the cracks and pores are filled with water.

这里的which和后面的一句话是which引导的名词性从句吗？
water table到底在cracks and pores的上面还是下面？

这是主系表结构包含了定语从句。
the water table是主语， is是谓语，the underground boundary是表语。
below which这里which指的是 boundary，所以是定语从句。
all the cracks and pores are filled with water是完整主谓宾结构，所以below which一起在句中做状语。

crossing the stream，he threw the tranking dogs off。 crossing the stream，非谓语动词（现在分词形式）引导状语从句，he 主语threw谓语 the tranking dogs off宾语

答案是：water table在cracks and pores的上面。below which意思是在它下面，这里的它是代指the water table地下水位(线).。全句是由两个分句构成的并列句而非复合句。拆开看是：The water table is the underground boundary. Below the water table all the cracks and pores are filled with water. 不知我说明白没有。祝进步!