A discussion of up-flow springs

ZHOU Xun, WANG Xiao-cui, CAO Qin, LONG Mi, ZHENG Yu-hui, GUO Juan,SHEN Xiao-wei, ZHANG Yu-qi, TA Ming-ming, CUI Xiang-fei

1School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China.

2Key Laboratory of Groundwater Circulation and Evolution (China University of Geosciences, (Beijing)),Ministry of Education, Beijing 100083, China.

3School of Environmental Science and Engineering, Qingdao University, Qingdao, Shandong 266071, China.

4Education Centre of Jiangxi Geological Exploration Bureau, Nanchang, Jiangxi 330030, China.

Abstract: Based on their genesis, springs are commonly classified as depression spring, contact spring, overflow spring and fault spring, etc. In addition, a kind of springs, i.e., up-flow spring,can be found in the field. An aquifer is overlain by poorly-permeable unconsolidated sediments or relatively impervious formations. If the hydraulic head of the aquifer is higher than the land surface, groundwater may flow up to the ground surface through the local portion of the overlying aquicludes where the permeability is relatively good, and emerges as an up-flow spring. The common characteristics of an up-flow spring are discussed and summarized in this paper, and some examples of the up-flow springs are also given. Up-flow springs can flow up through local permeable zones in the overlying aquicludes rather than permeable faults.Although they cannot be found as frequently as depression springs, contact springs, overflow springs and fault springs etc., yet up-flow springs may occur in the form of normal-temperature springs, hot springs and salt springs.

Keywords: Spring; Hot spring; Salt spring; Groundwater; Genesis

Introduction

A spring is a point or a location of water flow where groundwater originates from an aquifer or aquifers to the ground surface. It is the point of groundwater natural discharge in an aquifer or aquifers. Through a spring, groundwater emerges to the ground surface when the spring is continually replenished from the aquifer. Springs are commonly encountered in valleys and slope toes of mountain areas and in the piedmont areas and occasionally in slopes of mountain areas.Springs are of great significance in studies of groundwater circulation and for the purpose of water supply.

Springs are classified according to different considerations, and classification of springs was performed about 100 years ago by Bryan (1919)and others. According to temperature, springs can be classified into normal-temperature springs (the temperature of the springs is close to the local annual average air temperature), cold springs (the temperature of the springs is obviously lower than the local annual average air temperature), hot springs (the temperature of the springs is obviously higher than the local annual average air temperature and is equal to or higher than 25 ℃) and boiling springs (the temperature of the springs is close to and higher than the local boiling temperature) (ZHOU Xun et al. 2009; ZHOU Xun et al. 2014a). According to total dissolved solids(TDS) of the spring water, springs can be classified into fresh springs (TDS less than 1 g/L), brackish springs (TDS ranging from 1 to 10 g/L), saline springs (TDS ranging from 10 to 35 g/L) and salt springs (TDS greater than 35 g/L). These classifications of springs focus on the physical and chemical parameters of springs (YANG Li-zhong and HUANG Da-chun, 1989; ZHOU Xun et al.2010).

Special attention has been paid by many researches to the classification of springs based on their genesis. According to the genesis, Bryan K(1919) classified springs into depression spring,contact spring and artesian spring, etc. Bear J(1979) classified springs into depression spring,perched spring, fissure spring and spring in a confined aquifer. Alfaro C and Wallace M (1994)classified springs into karst spring, glacial spring,and thermal spring, etc. Fetter C W (2001)classified springs into depression spring, contact spring, fault spring, sinkhole spring and fracture spring. Pentecost A (2005) classified springs into gravity spring, depression spring, fault spring, and overflow spring, etc. Springer A E and Stevens L E(2009) classified springs into cave spring, exposure spring, geyser, and hanging spring, etc. WANG Da-chun et al. (1995) and ZHANG Ren-quan et al.(2011) classified springs into depression spring,contact spring, overflow spring, fault spring and contact zone spring. China Geological Survey(2012) classified springs into perched spring,depression spring, contact spring, overflow spring,ascending depression spring, fault spring and contact zone spring. ZHOU Xun et al. (2009) and ZHOU Xun et al. (2014a) classified springs into depression spring, contact spring, overflow spring,up-flow spring and fault spring, etc. Kresic N and Stevanovic Z (2010) classified springs into fracture spring, cave spring, gravity spring, artesian spring,contact spring and depression spring, etc. In addition, as a combination of the above-mentioned springs, springs like contact overflow spring,depression overflow spring, depression fault spring and depression contact overflow spring can also be encountered in the field (ZHOU Xun et al. 2009;ZHOU Xun et al. 2014a). This article focuses on the formation of the overflow springs.

1 Classification of some kinds of springs

Based on the relationship between the spring’s threshold and the lowest position of groundwater circulation in the aquifer which replenishes the spring, springs can be classified into springs of shallow groundwater circulation and springs of deep groundwater circulation. In the fractured rocks in mountain areas, fractures nearly do not develop at a certain depth below the land surface.Precipitation infiltrates and penetrates to the depth,and groundwater converges and finally emerges in the form of a spring at a lower topography. If the lowest position of groundwater circulation is still higher than the spring’s threshold, this kind of spring is called a spring of shallow groundwater circulation. If the lowest position of groundwater circulation is lower than the spring’s threshold, this kind of spring is called a spring of deep groundwater circulation, which is commonly encountered in the field (ZHOU Xun et al. 2009;ZHOU Xun et al. 2014a). For example, the threshold of Ningchang salt spring in Wuxi County in eastern Sichuan Basin is approximately 8 m higher than the water stage of the nearby river. The salt spring originates from the Triassic carbonates in the northern bank of the river, and aquicludes and faults do not exist in the vicinity of the spring.The Nichang salt spring is a spring of shallow groundwater circulation (ZHOU Xun et al. 2014b).

Springs of a special genesis, i.e., up-flow springs (Yong Liu Quan or Yong Chu Quan in Chinese pronunciation), can be observed in the field. They were first defined by ZHOU Xun et al.(2009, 2014). An aquifer is overlain by unconsolidated sediments of relatively low permeability or by relatively impervious formations. The hydraulic head of the aquifer is higher than the land surface.Groundwater can flow up to the land surface as an up-flow spring through the local zones of relatively high permeability in the unconsolidated sediments or impervious formations. An up-flow spring is characterized by: (1) The confining feature of the aquifer from which the spring emerges and the higher hydraulic head than the land surface near the spring’s threshold, (2) the existing local zones of relatively high permeability in the overlying unconsolidated sediments or impervious formations, and (3) no existing faults as permeable channels.

2 Examples of up-flow springs

Up-flow springs occurring in the field are not found as frequently as depression spring, contact spring, overflow spring, and fault spring, etc.Fig. 1 presents schematic profiles showing 8

situations of up-flow springs. Fig. 1A shows an up-flow hot spring originating from the piedmont area, where the carbonate aquifer outcrops in the mountain area and is overlain by Quaternary unconsolidated sediments in the plain area.Groundwater receives recharge from infiltration of precipitation in the mountain area and flows to the plain area. After being heated by the heat flow from below, groundwater flows up through the local zone of relatively high permeability in the Quaternary unconsolidated sediments to the land surface. The Xiaotangshan hot spring in the Xiaotangshan geothermal filed (BAI Tie-shan and LI Xin-Yu, 1989) to the north of Beijing is close to this situation. Fig. 1B shows an up-flow hot spring emerging in the middle of an inter-mountainous down-faulted basin in Yangyuan County of Hebei Province. Groundwater receives recharge from infiltration of precipitation in the surrounding mountain areas and flows to the basin area. After being heated by the heat flow from below,groundwater flows up in the center of the basin through the local zone of relatively high permeability in the Quaternary and Neogene unconsolidated sediments to the land surface.Fig. 1C shows the formation of the Xiannvshan hot spring in the northeastern Sichuan Basin. The carbonate aquifer of the Middle Triassic Leikoupo Group and the Lower Triassic Jialingjiang Group is overlain by the sandstone aquiclude of the Upper Triassic Xujiahe Group. A river valley in the sandstone aquiclude forms owing to the incision of a local river. After receiving recharge from infiltration of precipitation in the outcropping mountain areas and being heated by the heat flow from below, groundwater flows to a certain place below the river valley and up through the local fractured zone in the sandstone aquiclude to the land surface. Several saline springs in the eastern Sichuan Basin are similar to the situation in Fig. 1C. Fig. 1D shows an up-flow spring emanating from the slope toe. The confined carbonate aquifer is underlain and overlain by sandstone aquicludes. After receiving recharge from infiltration of precipitation in the outcropping mountain areas, groundwater flows towards a low-topographic valley and up through the fractured zones in the overlying sandstone aquiclude to the land surface. Fig. 1E shows the groundwater occurrence and flow direction in an alluvial fan in the piedmont region. From the fan head to the fan front, the unconsolidated sediment aquifer changes from being coarse-grain,unconfined and one-layered to being fine grain,confined and multi-layered. After receiving recharge from infiltration of precipitation in the fan head area, groundwater flows towards the plain area in one of the confined aquifers and up through the local zone of relative high permeability in the overlying clay aquiclude to the land surface.Fig. 1F shows an up-flow hot spring in a granite region. A fault zone occurs in the granite rock and is overlain by Quaternary unconsolidated sediments. Groundwater circulates in the fault zone and receives the heat from below. The hot water flows up along the fault zone and through the Quaternary unconsolidated sediments and to the land surface, emerging as a hot spring. This kind of spring is also called an up-flow fault spring. The hot springs which once existed in the cities of Fuzhou (CHEN Mo-xiang et al. 1994) and Zhangzhou (WANG Ji-yang et al. 1993) in Fujian Province are similar to this situation. Fig. 1G shows the formation of an up-flow spring located to the east of Jinzhong (Yuci) in Shanxi Province,although the spring dried up about 40 years ago due to over-exploitation of groundwater in the nearby water supply wells. Groundwater in the fractured sandstone aquifers of the Lower Triassic Liujiagou Group and the Middle Triassic Ermaying Group received recharge from infiltration of precipitation in the eastern mountain area and flowed to the west and up through the fractured zone in the aquiclude of mudstone inter-bedded with sandstone of the Lower Triassic Heshanggou Group and the permeable zones in the Quaternary unconsolidated sediments and to the land surface.Fig. 1H shows the occurrence of fault springs and up-flowing springs in western part of the huge sedimentary basin, the Great Artesian Basin, in Australia. The Jurassic-Lower Cretaceous aquifer is overlain by the Upper Cretaceous aquitard and Quaternary unconsolidated sediments. Groundwater in the Jurassic-Lower Cretaceous aquifer is in an artesian state. Groundwater rises along the permeable faults, permeable fractures and permeable fractured zones and through the Quaternary sediments to the land surface.

Fig. 1 Schematic profiles showing eight overflow springs

3 Conclusions

Up-flow springs are seldom examined and understood in the previous hydrogeologic investigations. An up-flow spring is different from other types of springs in that the confined aquifer from which the up-flow spring is replenished is overlain by consolidated or unconsolidated aquicludes.Local permeable zones other than permeable faults exist in the overlying aquicludes. Under suitable topographic conditions, groundwater in the aquifer flows up through the local permeable zones to the land surface. An up-flow spring is a kind of ascending springs. Up-flow springs can be found in the piedmont areas, the intermountainous downfaulted basins and sedimentary basins, as well as river valleys. They are not so frequently encountered as depression springs, contact springs,overflow springs and fault springs. They can be normal-temperature springs, hot springs and saline or salt springs.

Acknowledgements

This work was cooperatively supported by the Natural Science Foundation of China (41572223,41172227), the Natural Science Foundation of Beijing (8152026), the Fundamental Research Funds for the Central Universities of China(2652015244, 2652015245, 2652015426) and the National Key Project of Foundational Research and Development of China (973 Project)(2011CB403005).