Nathalie Molines is a lec­tur­er-cum-research sci­en­tist at the UTC-Avenues lab­o­ra­to­ry in the Depart­ment of Urban Engi­neer­ing. Togeth­er with Katia Chancibault from the Water and Envi­ron­ment Lab­o­ra­to­ry (LEE) at Gus­tave-Eif­fel Uni­ver­si­ty, 77420 Champs-sur-Marne and Bernard de Gou­vel­lo from CEREMA, she co-super­vised Saray Chavez’s the­sis (2020–2024).

Focus­ing on the impact of urban plan­ning doc­u­ments on r ain-water man­age­ment at the source, Saray Chavez’s the­sis was hon­oured at the 2025 “Grand Prix” (for urban con­text the­ses). It also received the 2025 Open Sci­ence The­sis Award in the “inter­dis­ci­pli­nary and trans­verse” cat­e­go­ry. For a long time, rainwater—often con­sid­ered a waste product—has been dis­charged (via com­bined or sep­a­rate sew­er sys­tems) to waste­water treat­ment plants. Dur­ing heavy rain­fall spells, these sys­tems can become over­whelmed, lead­ing to the direct dis­charge of untreat­ed water into the nat­ur­al envi­ron­ment. Fur­ther­more, runoff from imper­vi­ous sur­faces con­tributes to water pol­lu­tion before it enters the sew­er systems.

Rain­wa­ter man­age­ment at the source offers a dif­fer­ent approach: pro­mot­ing water infil­tra­tion where it falls, par­tic­u­lar­ly through veg­e­ta­tion and reduc­ing soil imper­vi­ous­ness. This strat­e­gy reduces the vol­ume of water dis­charged into the sys­tems, while help­ing to com­bat urban ‘hot spots’, enhance bio­di­ver­si­ty and gen­er­al­ly improve qual­i­ty of life.

Its imple­men­ta­tion, how­ev­er, depends heav­i­ly on local urban plan­ning (PLU), which trans­late pub­lic pol­i­cy goals into build­ing reg­u­la­tions. Through these reg­u­la­tions, they can encour­age “green­ing”, lim­it soil seal­ing, or man­date rain­wa­ter man­age­ment sys­tems at the source.

Two com­ple­men­tary approach­es have been devel­oped. The first, qual­i­ta­tive, analy­ses the life cycle of an urban plan­ning reg­u­la­tion, from its draft­ing to its appli­ca­tion dur­ing the review of a build­ing or devel­op­ment per­mit. The sec­ond, quan­ti­ta­tive and spa­tial­ized, cross-ref­er­ences the char­ac­ter­is­tics of urban plan­ning rules with those of a pan­el of 23 alter­na­tive solu­tions tai­lored to the speci­fici­ties of the ter­ri­to­ry to pro­duce an imple­men­ta­tion poten­tial index. This tool makes it pos­si­ble to esti­mate the influ­ence of reg­u­la­tions on the imple­men­ta­tion of each solu­tion and to assess their suit­abil­i­ty for the region’s needs.

This the­sis is part of a col­lab­o­ra­tive research ini­tia­tive, close­ly involv­ing researchers and oper­a­tional stake­hold­ers from the Nantes met­ro­pol­i­tan area. Co-cre­ation work­shops were orga­nized through­out the the­sis to test sci­en­tif­ic hypothe­ses against oper­a­tional prac­tices, refine method­olog­i­cal choic­es and val­i­date the tools and indi­ca­tors devel­oped. This direct involve­ment of local agen­cies strength­ened both the sci­en­tif­ic robust­ness of the results and their adop­tion by local stakeholders.

This research brings togeth­er three dis­ci­plines that have his­tor­i­cal­ly had lit­tle inter­ac­tion: reg­u­la­to­ry urban plan­ning, ter­ri­to­r­i­al deci­sion sup­port and urban hydrol­o­gy. This mul­ti­dis­ci­pli­nary approach served as a key lever for con­duct­ing orig­i­nal research at the inter­face between sci­en­tif­ic out­put and pub­lic action.

“Local author­i­ties often devel­op urban plan­ning reg­u­la­tions with­out hav­ing tools that allow them to con­crete­ly antic­i­pate their effects on ter­ri­to­r­i­al adap­ta­tion. This the­sis helps fill this gap by propos­ing a method of analy­sis and deci­sion sup­port, test­ed using the case of the Nantes Met­ro­pol­i­tan Area,” notes Nathalie Molines.

This momen­tum is being extend­ed. The ANR so-called Per­mépo­lis project explores the issue of urban de-imper­me­abi­liza­tion. A new the­sis, launched last Octo­ber (fund­ed by Gus­tave-Eif­fel Uni­ver­si­ty), is also under­way. Super­vised by the same research team, it focus­es on the devel­op­ment of adap­ta­tion sce­nar­ios and their hydro­cli­mat­ic assessment.

MSD