Managed aquifer recharge via infiltratio

1 Managed aquifer recharge via infiltration ditches in

2 short rotation afforested areas

3

M. Mastrociccoa

, N. Colombani b#, E. Salemia

, B. Bozc

, B. Gumierod

4

5

a 6 Department of Physics and Earth Sciences, University of Ferrara, Via Saragat, 1 - 44122 Ferrara, Italy

b 7 Department of Earth Sciences, “Sapienza” University, P.le A. Moro, 5 - 00185 Rome, Italy

c

8 Freelance consultant, Bioenergy and Climate Change Department, Veneto Agricoltura, Viale dell'Università, 14 -

9 35020 Legnaro (PD), Italy

d 10 Department of Biological Geological and Environmental Science (BiGeA), Bologna University, Via Selmi, 3 - 40126

11 Bologna, Italy

12

# 13 Corresponding author: Tel.: ++39 0532 974692, Fax: ++39 0532 974767

14 E- mail address: [email protected]

15

16

17 Abstract

18 Managed aquifer recharge (MAR) design and operation must incorporate the expected long-term

19 performance from a water quantity perspective to sustainably mitigate hydrologic impacts of

20 groundwater overexploitation. Gravity driven infiltration ditches in forested areas are one of many

21 MAR scheme that could augment the available water resources. Research on the longevity of these

22 structures is sparse, leading to concerns about their long-term capability to sustain elevated

23 infiltration capacity. In the present study, an infiltration system consisting of a regular grid of eight

24 ditches divided into 4 sequential plots within a short rotation forested area (AFI) was monitored

25 from its inception to determine its hydrologic performance over time and its possible export to

26 similar areas of the Brenta Megafan (Northern Italy). During the monitored period, the AFI was not

27 significantly affected by clogging since the suspended solids carried by the Brenta River water

28 diversion were extremely low. The main source of clogging was the fallen foliage during the

29 autumn, easily managed via ordinary maintenance. The AFI displayed an almost constant

30 performance to infiltrate the diverted water over the first three years of operation, with a total

amount of infiltrated water of approximately 0.8 Mm3

31 /ha/y. The best tracer to reconstruct the

32 downward water movement through this highly permeable vadose zone was temperature, while the

33 groundwater table fluctuation could not be used to infer the effective infiltration, because of its

34 large seasonal variability. The good results suggest that promote this technique in other areas of the

35 Brenta Megafan that suffer from groundwater resources depletion.

36 1. Introduction

37 Groundwater resources represent about 98% of liquid freshwater on earth and are thus critically

38 important to satisfy urban, agricultural, industrial and environmental needs (Aeschbach-Hertig and

39 Gleeson, 2012). To guarantee further agricultural and municipal development required by the fast

40 demographic growth, in many regions water authorities will rely more heavily on groundwater in

41 coming decades (Green et al., 2011). Nevertheless, groundwater resources are still generally

42 undervalued, disregarded and often inadequately managed and protected, both in semi-arid and

43 humid regions of the world (Foster et al., 2013).

44 Anthropogenic perturbation of groundwater systems is remarkable in the last century, as a result of

45 over extraction for urban water supply, agricultural practices and land-use changes in recharge

46 zones. In many areas, this has caused a decline in the water table resulting in environmental

47 problems, like adverse impact on groundwater-fed wetlands of high ecological value (Herrera￾48 Pantoja et al., 2012; Holländer et al., 2009). Moreover, the variations of the regional hydrologic

49 cycle related to climate change (especially the intensity, location, and seasonal variability of

50 precipitation); also pose challenges for the sustainable management of groundwater resources and

51 related ecosystems (IPCC, 2014a, b).

52 To address these issues a wise groundwater management is urgently required. Most experts agree

that a considerable part of the increased water demand in the 21st 53 century will need to be met by an

54 increased water storage capacity (Bouwer, 2002). Conventionally, such storage is achieved with

55 dams and surface reservoirs. Though, dams have various disadvantages such as evaporation losses,

56 sediment accumulation, potential of structural failure, high costs for construction and maintenance,

57 adverse ecological, environmental and socio-cultural effects (Wang et al., 2012; Xie et al., 2014).

58 As aquifers offer vast opportunities for underground storage of water, managed aquifer recharge

59 (MAR) is expected to become increasingly appealing in the near future (Dillon, 2005), not only

60 because it provides essentially zero evaporation but also because economic and other aspects of

61 recharge are often favourable (Dagès et al., 2008; National Research Council, 2008).

62 MAR encompasses a series of strategies and techniques for increasing percolation towards an

63 aquifer, using excess flows in streams or channels, agricultural return flows or treated waste water

64 (Bouwer, 2002; Greskowiak et al., 2005; Heilweil and Watt, 2011; Massmann and Sültenfuß, 2008;

65 Prommer and Stuyfzand, 2005).

66 MAR systems need permeable soils to get high infiltration rates and to minimize land requirements,

67 a vadose zone free from fine-textured materials, unconfined and sufficiently transmissive aquifers

68 to guarantee lateral flow of the infiltrated water (Perkins et al., 2014; Racz et al., 2012; Reese,