# Groundwater and Urban Planning Perspective
## 2 Exploring the Connection between Urban Development and Urban Subsurface Hydrology
### Land Instability in Bucharest City  
Located in southeastern Romania, with an area of approximately 240 km\({}^{2}\) and a population of over 2.1 million inhabitants [31], Bucharest is crossed by two rivers: the Dambovita and Colentina. The first is extensively canalized and the second was reshaped at the beginning of the 20 th century in a series of chained lakes [32], which have a direct hydraulic connection to the shallow aquifer. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Region** & **Name** & \begin{tabular}{c} **Built Area Density** \\ **(Inhabitants/sq km)** \\ \end{tabular} & \begin{tabular}{c} **Population** \\ **(2019)** \\ \end{tabular} & \
\begin{tabular}{c} **Function** \\ **Function** \\ \end{tabular} &
\begin{tabular}{c} **GUP Elaborated in** \\ \end{tabular} \\ \hline Northeast & Iasi & 6347.08 & 382,767 & municipality & 1999 \\  & & & (CRM) & \\ Northeast & Bacau & 5819.05 & 197,097 & CRM & 2009 \\ Southeast & Constanta & 5372.78 & 312,250 & CRM & 2010 \\ Southeast & Galati & 5172.35 & 305,386 & CRM & 2017 \\ Southeast & Braila & 7017.42 & 201,414 & CRM & 2021 \\ South & Ploiesti & 4293.23 & 226,133 & CRM & 2017 \\ South & Pitesti & 7043.76 & 173,537 & CRM & 2021 \\ Southwest & Craiova & 5286.90 & 300,375 & CRM & 2000 \\ West & Timisoara & 5333.53 & 326,636 & CRM & 2021 \\ West & Arad & 3165.74 & 176,455 & CRM & 1998 \\ Northwest & Cluj Napoca & 4810.47 & 326,145 & CRM & 2018 \\ Northwest & Oradea & 2987.65 & 221,301 & CRM & 2021 \\ Northwest & Baia Mare & 3844.24 & 145,220 & CRM & 1999 \\ Centre & Brasov & 3223.75 & 289,190 & CRM & 2010 \\ Centre & Sibiu & 5211.81 & 168,477 & CRM & 2010 \\ Centre & Tägui Mures & 5442.24 & 147,305 & CRM & 2010 \\ Bucharest-Ilfov & Bucharest & 8903.9 & 2,139,493 & Country capital & 1998 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the selection criteria. Figure 2: The location of the chosen 17 cities on the Romanian map. Map generated in Esri® ArcMapTM 10.3. Base map source: ESRI. Source: elaborated by the authors. Bucharest is a dynamic city with an expanding population and surface coverage, and thus its infrastructure shows considerable development and subsurface changes. Aspects of urban development in connection to groundwater dynamics have been highlighted. Two parallel directions of study have followed: the examination of the current urban development and planning framework and a land instability analysis (Figure 1). Considering the particularities of the subsidence phenomena, two time periods have been considered, for which data sets from two European satellite radar missions were available. Thus, for the 2004-2010 period, data from the ENVISAT ASAR mission have been used and processed using the Persistent Scatterer Interferometry (PSI) technique. For the 2014-2018 period, data from the current European radar mission (Sentinel-1) has been used. Maps of the vertical displacements of the terrain for the entire urban area were generated using these data sets for the two time intervals mentioned above. The consistency of the results for the two time intervals has been observed by analyzing two corresponding land displacement maps. Numerous areas of instability that were identified on the land displacements map for the 2004-2010 interval show the same trends as for the 2014-2018 interval. Alongside the PSI technique, a land surface change detection technique was used for a better interpretation of the changes and displacements at the land's surface level. A new cartographic product has been obtained through combining the map of the vertical land displacements with the surface terrain change detection map [28]. Therefore, the potential areas that locate the source of vertical displacements have been established accurately. The chosen area is located along the Colentina River corridor (Figure 3). For the 2014-2018 period, a methodology to characterize the area has been proposed.