 So, good day everyone, I'm very honored to share with you a case study that I've been working on is assessing the impact of managed aquifer recharge on the groundwater system in Yongding River catchment by numerical modeling. As you may know, Beijing is the capital of China, it's under rapid urban development and the total population is around 22 million at the end of the year 2020. However, the average annual precipitation is only 585 millimeter per year and this very uneven temporal distribution amount of year. 60% of the water supply relies on the groundwater resources, however, because of a 10-year drought from 1999 until 2009, the city's water resources has been overdrafted, the rivers was cut off, groundwater was heavily overexploited which also arouses other kinds of environmental problems in the city and the city was seeking for a solution to this water scarcity problem. One of the opportunities are the large-scale water transport projects and one of them is transferring the yellow river water from the neighboring provinces to the Yongding River catchment in China, in Beijing and the water diverted from the yellow river will be released from the upstream reservoir to the river channel and on the one hand these water release helps to maintain the environmental flow and at the same time the infiltration from the riverbed is augmenting the groundwater recharge and the water will first go through the mountain area before it arrives in the plain area of the city and then the discharge is controlled by a sluice which could regulate the water release rate and the duration to the downstream mar site which is the main research area of this study. And this mar site at the urban area along the Yongding River channel has been constructed into several lakes and the wetland parks which functions as the recreational spaces for the citizens and at the same time also largely improved the river ride ecosystem and during the release from the upstream sluice the released water will be recharged to the aquifer and the total infiltration area is around 10.4 kilometer square. So since 2019 the water release from these sluice has been tested before and after the flood season with different release rate and duration and in 2019 in the springtime 132 million cubic meters were released during 93 days and 151 million cubic meter has been released in 2020 spring during 32 days and the other 15 million cubic meters were released during 22 days in 2020 autumn. So in order to assess the impact of this mar project on the groundwater system we would like to use groundwater modeling to do a simulation and we expect that by this construction of a 3D groundwater model we could compute the spatial distribution of the groundwater level changes time quantifying the recovery of the groundwater storage and the infiltration rate and the maximum infiltration capacity of the riverbed and also identify the potential hazards related to this mar project and in the end to optimize the future mar management in the area and this model construction is was based on a regional groundwater flow model of the urban city area of Beijing which simulates the monthly groundwater flow dynamic from 1995 until 2008 and in this case we locally refined the grid in the area of interest to simulate the response of groundwater system on the managed aquifer recharge and extend this model simulation period until 2020 with steady stress period and the model calibration was done by adjusting the hydraulic parameters to match the computed groundwater level with the observations and as can be seen most of the groundwater level changes with time at the observation wells can be well captured which verifies the accuracy of this model simulation and here is the the groundwater level contour map during the three water release event and the groundwater level under the riverbed and the surrounding areas has been increased significantly and the maximum groundwater level increase can be more than 20 meters and from the water balance results we could clearly see that during the groundwater storage has been restored after the implementation of the managed aquifer recharge and compared to the beginning of 2018 the groundwater recharge has been increased in total 85 million cubic meters and the infiltration rate for a different part of the marsh side has also been calculated because of the different hydrogeological conditions from the north part to the south part of the marsh side the infiltration rate for different lakes and wetlands also varies from 0.7 meters per day up to 0.05 meters per day so the surface water and the groundwater actually are hydraulic disconnected at the upstream so the infiltration rate can always maintain the maximum all the time however at the downstream part after the groundwater level increased during the water release events groundwater and surface water body becomes hydraulic connected so the high infiltration rate can no longer be maintained therefore it is predicted that in the future the infiltration capacity of the downstream lakes and wetlands will get lower and another aspect we concern is the efficiency of this water release on recharging the groundwater storage so compared to the total water released from the upstream smooth the groundwater recharge efficiency of 2019 screen is around 15 percent or 15 percent higher than the other two events in 2020 because it has a relatively longer recharge period and moderate water release rate but overall the majority part of the released water have been infiltrated through the river channel and restored the groundwater storage and besides all the potential all the positive impact of this the MAR project some potential hazards should also be addressed like here we mapped the area with more than three meters groundwater level increased and the area with less than 10 meters groundwater depth after the MAR operation at in November 2020 and then the increase of the water level might result in the groundwater pollution since there are several old waste disposal sites in the study area and these shallow groundwater depths might do damage to some underground infrastructures such as the metro stations or the basement of the buildings which also needs to be monitored frequently in the future and so from the results above some recommendations for the future MAR management of the Union River catchment can be draw for the MAR operation scheme that we could see longer release water release duration and lower release rate could improve the groundwater recharge efficiency and for the risk control aspects like the high groundwater level needs to be aware during the MAR implementation and overall this groundwater model reconstructed can be a very effective tool to support the decision makers to test a different future groundwater recharge scenarios and assess the impact of the MAR operation in this highly urbanized groundwater environment and I think that's all I would like to share until now and welcome all kinds of questions thank you thank you Siva thank you very much if you can stop sharing your screen they can all see us a bit better again and indeed I would ask all the people attending or attendance to add your questions also to their question and answer box meanwhile we have received a few already and we have some time to address them so as to that Mooneep is asking how many groundwater monitoring wells where there are were used to quantify the groundwater in your case study and what was the overall time scale or the time the period of observations which you based your results thank you thank you Siva and thanks for the questions Mooneep in total when we construct this regional groundwater model there were 202 observation wells through the Beijing Plain area which is the counts for 6,500 kilometer square from the shallow aquifer until the deep aquifer but most of the observation wells were in the shallow aquifer and it's the kind of combined pumping wells also functions as the monitoring wells and in this Yongding River catchment the MAR site we studied in this research they were in total 77 groundwater monitoring wells specifically just around the MAR site which some of them just located exactly near the riverbed and some are a little bit further which that we could use them to see the impact area of this MAR site and also at the same time calibrate to this model yeah that's quite an impressive number of monitoring wells I would say and before I go on to the next question I had one link to that you mentioned the rising water level could cause challenges and I'm wondering how much of the recharge to ground waters being recovered by wells by pumping wells do you have an idea so is or is it purely recharge without really looking into let's say recovery of the of the recharge water to avoid also that rise to that would be excessive in this part of the MAR site we don't really have an intensive groundwater obstruction the most of the recharge water will just stay in the aquifer as a storage and gradually spread during the in the unconfined aquifer and which we believe that with the long-term operation it can it will spread further which will actually benefit for the drinking water production and also worse to mention we have another MAR pilot study in another catchment in this area which is exactly located next to well field groundwater well field so in for that one the most of the recharged water will be directly abstracted as the groundwater pumping which it's a kind of a sustainable way of using this recharged water this actually links to abraham's question from the audience which is also a challenging one I think the question is what is the comparative advantage of using these targeted localized recharge methods along the river as compared to improving infiltration over the entire aquifer or the entire hydrological unit what do you think I would like to say firstly this is actually a very highly urbanized area we don't really have so many space for the large-scale infiltration to to replenish the whole hydrological unit and with this specific site recharge on the one hand it's actually it recharges the groundwater that is our main concern here but at the same time it also has some side benefit like the constructed wetlands parks that we the people just could just have a walk there to enjoy a natural sense in a very urbanized area like my parents would just go there for during the weekend for a walk which they really enjoying and at the same time this riverbed also actually was implement some liner at the bottom so the recharged water will be stayed in the river as an environmental flow which also benefits the riverized ecosystem that is also a side benefit so that's what I would say the benefit of this interesting yeah