Grundvattenbildning till berg- En litteraturstudie samt fallstudie av järnvägstunneln delen Varberg-Hamra

Sammanfattning: Both globally and from an individual perspective, water is the most important resource we have on earth. Knowledge of groundwater and groundwater recharge is important from many perspectives, such as environmental, socio-economic and structural engineering. The thesis is written at Lund University in Environmental sciences and aims to highlight groundwater recharge to the crystalline bedrock and groundwater recharge when tunneling in hard rocks. The paper also houses a case study of Västkustbanan part Varberg-Hamra, where local groundwater recharge is estimated. The question is what determinates groundwater recharge during normal geological conditions and when tunneling and whether these differ. The literature study shows that for Sweden, groundwater recharge to bedrock depends on several factors such as the hydraulic contact between soil and rock, rock mechanics and hydraulic properties as well as the overlying layers permeability. Groundwater recharge to bedrock takes place mainly through the soil and is greatest in topographic highs and in areas where the rock is heavily fractured. The study also shows that only a very small part of the groundwater in the soil forms groundwater in rock. Groundwater in rock is controlled largely by the rock fractures and fracture zones. Main groundwater recharge in tunnel areas works in the same way as for normal groundwater recharge to bedrock, the difference being an increase in recharge because a tunnel acts as a drainage center. The size of the increase is determined by the rate of leakage into the tunnel and drainage of groundwater and on the hydrogeological context. Calculation of hydraulic parameters is possible for both cases, however, computer simulations are more common to evaluate and predict local conditions in terms of groundwater recharge, leakage into the tunnel and lowering of the water table. In the case study, an estimated groundwater recharge is calculated to be 0.34 m3/ m2/year before tunneling under current conditions. The evaluation of the pumping test in Varberg gave a hydraulic conductivity of the pumped soil-bedrockaquifer to 5x10-6 m/s. The semipermeable layer had a vertical leakage rate which was estimated on average to 5x10-8 m/s, resulting in a leakage from 6x10-4 to 3x10-5 m3/s at transient conditions. The leakage per day at transient conditions was calculated to 2300 l, which may result in negative environmental consequences.