Abstract
A hydrogeological study of the Nossana Spring (Val Seriana, Bergamo, Italy) is presented with the aim of assessing the spring’s depletion risk. In the last few years, the discharge of the Nossana Spring showed a decreasing trend, similar to the trend of many other springs in the Prealpine Region. The study was carried out using a groundwater flow model to simulate the depletion curve of the spring in different recharge conditions. The simulations have shown that the depletion curve of the Nossana Spring depends on the recharge during the previous season. As a result, a negative exponential relation giving the spring depletion curve as a function of the recharge was obtained. This relation was also used to statistically calculate the actual probability of the occurrence of a deficiency in water resources, which for the present day is equal to 2%. Finally, the effect of climate change was considered, showing in the next 100 years a flat decline of about 40% in the average spring discharge and a considerable shortening of the critical length (the time to reach the critical discharge at which supply problems occur) in the dry season, which will be halved by the end of the century.
Résumé
Une étude hydrogéologique de la source Nossana ( Val de Sériana, Bergame, Italie) est présentée avec pour objectif l’évaluation du risque de tarissement de la source. Au cours des dernières années, le débit de la source Nossana a montré une tendance à la diminution, similaire à la tendance observée pour des nombreuses sources de la région préalpine. L’étude a été menée en ayant recours à un modèle hydrogéologique afin de simuler la courbe de récession de la source pour différentes conditions de recharge. Les simulations ont montré que la courbe de tarissement de la source est influencée par la recharge de la saison précédente. Une relation de type exponentiel négative permet d’expliciter la courbe de récession de la source en fonction de la recharge. Cette relation a été utilisée pour calculer de manière statistique la probabilité d’occurrence d’un déficit de la ressource en eau; celle-ci est équivalente pour le présent à 2%. Enfin, l’effet du changement de climat a été considéré, montrant qu’au cours de cent prochaines années la possibilité d’une diminution de quelques 40% du débit de la source en moyenne et une réduction considérable de la longueur critique (temps pour atteindre le débit critique à partir duquel des problèmes d’alimentation en eau surviennent) en période de sécheresse, soit une division par deux d’ici la fin du siècle.
Zusammenfassung
Es wird eine hydrogeologische Studie vorgelegt, um die Gefahr der Absenkung der Quelle Nossana (Val Seriana, Bergamo, Italia) zu untersuchen. Schon in den vergangenen Jahren wurde eine Tendenz zur Reduzierung des Wasserflusses beobachtet, die der anderer voralpiner Quellen gleicht. Es wurden mit einem unterirdischen Strömungsmodell die Absenkungsraten der Quelle unter verschiedenen Auffüllungsbedingungen dargestellt, wobei das Verhältnis zwischen der Absenkungskurve der Quelle Nossana und der Auffüllungsrate der Vorjahressaison hervorgehoben wird. Es wurde eine negative Exponentialfunktion entdeckt, mit der sich die Absenkungskurve der Quelle unter Berücksichtigung der Auffüllung bestimmen lässt. Dieses Verhältnis wurde zur statistischen Auswertung herangezogen, um die aktuelle Wahrscheinlichkeitsrate einer hydrologischen Krise herauszufinden, die mit 2 % angegeben wird. Zum Schluss wurden die möglichen Auswirkungen einer Klimaveränderung in den nächsten 100 Jahren unter Berücksichtigung eines Netto-Rückganges (ca. 40%) des durchschnittlichen Abflusses der Quelle und einer erheblichen Reduzierung der kritischen Trockenzeitdauer (im Sinne eines Zeitraumes in dem die Quelle eine kritische Strömungsgeschwindigkeit erreicht, die das von ihr gespeiste Wasserzuführungssystem in Gefahr bringen kann) analysiert, die am Ende des Jahrhunderts halbiert sein wird.
Resumen
Se presenta un estudio hidrogeológico del manantial de Nossana (Val Seriana, Bergamo, Italia) con el objetivo de evaluar el riesgo de depleción del manantial. En estos últimos años, la descarga del manantial de Nossana mostró una tendencia decreciente, similar a la tendencia de muchos manantiales en la región pre Alpina. El estudio fue llevado a cabo usando un modelo de flujo de aguas subterráneas para simular la curva de depleción del manantial en diferentes condiciones de recarga. Las simulaciones han mostrado que la curva de depleción del manantial de Nossana depende de la recarga durante la estación previa. Como resultado se obtuvo una relación exponencial negativa que da la curva de depleción del manantial en función de la recarga. Esta relación fue también usada para calcular estadísticamente la probabilidad real de la ocurrencia de una deficiencia en los recursos de agua, la cual actualmente equivale a 2%. Finalmente, se consideraron los efectos del cambio climático en los próximos 100 años, lo cual mostró un descenso parejo de cerca del 40% en la descarga promedio del manantial y una considerable reducción de la longitud crítica (tiempo para alcanzar una descarga crítica en que ocurren los problemas de alimentación) en la estación seca, la cual se verá reducida a la mitad hacia el final del siglo.
摘要
为评价其枯竭风险, 对意大利贝加莫Val Seriana城的Nossana泉进行了水文地质研究。在过去的几年, 与Prealpine地区许多其他的泉一样, Nossana泉的排泄量表现出下降的趋势。本次研究通过地下水流模型来模拟不同补给条件下该泉的枯竭曲线。模拟表明, Nossana泉的枯竭曲线取决于前一季节的补给量。由此得到泉的枯竭曲线是补给量的负指数函数。此关系也用于对水资源不足发生的实际概率进行统计计算, 当前概率为2%。最后, 考虑了气候变化的影响, 得出在未来的100年平均泉排泄量有约40%的平缓下降, 以及旱季临界长度 (达到临界排泄量的时间, 即补给问题出现的时间) 的显著缩短, 到本世纪末该长度会减半。
Riassunto
La nota propone uno studio idrogeologico finalizzato alla valutazione del rischio di esaurimento della Sorgente Nossana (Val Seriana, Bergamo, Italia). Negli ultimi anni, infatti, le portate di questa sorgente hanno evidenziato un tendenza alla decrescita, con un andamento simile a quello di molte altre sorgenti della fascia prealpina. Tramite un modello di flusso sotterraneo si sono simulate le curve di esaurimento della sorgente per diverse condizioni di ricarica, evidenziando la dipendenza dell’andamento della curva di esaurimento della Sorgente Nossana dalla ricarica della stagione precedente. E’ quindi stata individuata una funzione esponenziale negativa in grado di fornire la curva di esaurimento della sorgente in funzione proprio della ricarica. Tale relazione è poi stata utilizzata per valutare in termini statistici l’attuale probabilità di accadimento di un periodo di crisi idrica, risultata pari al 2%. Infine, si sono analizzati i possibili effetti derivanti dal cambiamento climatico, evidenziando per i prossimi 100 anni una decrescita netta (pari a circa il 40%) della portata media della sorgente e una notevole riduzione della durata critica della stagione asciutta (intesa come il periodo di tempo tale per cui la sorgente raggiunge una portata critica, cioè in grado di mandare in crisi il sistema acquedottistico da essa alimentato), che arriverà a dimezzarsi per la fine del secolo.
Resumo
Apresenta-se o estudo hidrogeológico da nascente Nossana (Val Seriana, Bérgamo, Itália), com o objectivo de avaliar o risco de esgotamento da nascente. Nos últimos anos, o caudal da nascente Nossana apresenta uma tendência decrescente, similar às tendências de muitas outras nascentes na região Pré-alpina. O estudo foi conduzido recorrendo a um modelo de fluxo de águas subterrâneas para simular a curva de esgotamento da nascente em diferentes condições de recarga. As simulações mostraram que a curva de esgotamento da nascente Nossana depende da recarga durante a estação anterior. Como resultado, obteve-se uma relação exponencial negativa entre a curva de esgotamento da nascente e a recarga. Esta relação foi ainda utilizada para calcular estatisticamente a probabilidade real de ocorrer escassez nos recursos hídricos, que actualmente é de 2%. Finalmente, considerou-se o impacte das alterações climáticas, demonstrando-se que nos próximos 100 anos ocorrerá um declínio gradual de cerca de 40% no caudal médio da nascente e um decréscimo considerável da distância crítica (o tempo necessário para atingir o caudal crítico, em que podem ocorrer problemas no abastecimento) durante a época seca, que será reduzida para metade até ao final do século.
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Gattinoni, P., Francani, V. Depletion risk assessment of the Nossana Spring (Bergamo, Italy) based on the stochastic modeling of recharge. Hydrogeol J 18, 325–337 (2010). https://doi.org/10.1007/s10040-009-0530-3
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DOI: https://doi.org/10.1007/s10040-009-0530-3