The Application of Gray System Theory for Groundwater Level Prediction.

Groundwater is important water resource in Taiwan, especially for agriculture water use. Groundwater level represents the quantity of an aquifer which is pumped. The reasons including earth tide, atmospheric pressure, artificial pumping and recharge which cause groundwater level fluctuation are very complicated. Therefore prediction of groundwater level is a difficult study subject for hydrogeologists. Gray system theory is a robust tool for solving a physic problem which is complex or indistinct. Simple differential equations which are called gray models are used to identify the interaction relationship between several factors. Even the true behavior of these factors is unreliable, gray models also can provide satisfied prediction result. As mention above gray system theory is suit tool for groundwater prediction. This study used gray system theory to establish a prediction model for groundwater level in Taiwan. The groundwater level data and rainfall data were assumed as the two major factors of groundwater level. Using the past groundwater level and rainfall data , a GM(1,2) gray model was established. The prediction model was constructed with long term trend, period trend and random fluctuation. The result of prediction showed that the prediction result was sufficient for groundwater management by using gray system theory.