Paleofloods

Using paleoflood reconstruction techniques, it is speculated that a catastrophic flood occurred in Petra during the 4th to 5th century AD.  Evidence indicates that a low frequency (p= 0.001-0.0005), high magnitude event (4-6+m surge, 3+m/s velocity) would have devastated the city. Geomorphic characteristics were analyzed including the (i) exacerbating channel configurations along Wadi Mataha, (ii) relict, extant alluvia of Disi-derived sediments along Wadi Musa (in situ exposed, and in excavations), (iii) missing pavers along the Colonnaded Road that delineate the huge meanders produced during the event(s), and (iv) the location, morphology, and dimension of excavated flood-event alluvia flanking the channel of Wadi Musa. Using fluvial reconstruction formulae (i.e. Mannings, Chezy), in conjunction with the examination of these extant features in Wadi Mudhlim, Mataha and Musa, paleo-reconstructions of flood height and discharge, meander dimension, and velocity enabled the re-creation of the catastrophe. Dated strata excavated above and below the event deposits narrow its occurrence between the great earthquake of May 363 AD and the mid-5th Century. Excavated Disi deposits along the Colonnaded Road (shops XXVII-XXX), indicate that the water depth and torrent extent created floodwater meanders of amplitudes exceeding 45-50m, with a related stream power of 3-3.3m/s (enough to move 1-2m boulders). Suggestions of ‘periodic’ and ‘episodic’ flooding in Petra are common (p: 0.1-0.01), however flood levels that were catastrophic in nature, depth, velocity and turbulence (p: 0.005-0.0005), have not been addressed until today. Rushing floodwaters would have entered the Bab as-Siq at levels up to 2 to 3 meters in depth to accumulate creating surging high water that entered the Siq (to some degree), but found the northern channels of Wadi Mudhlim more suitable for flow. Water rushing down Wadi Mataha, would have accelerated from 0.5m/s to 1.1m/s, to jump past the confluence at the Nymphaeum, to rejoin the waters in Wadi Musa, creating a fantastic 5-8m flood bore, accelerating to 3.3m/s along the Colonnaded Road. The water surged down the street leaving boulders, heaps of gravel and pebbles in its wake. The road would have been blanketed by 2 to 5m of sediments. The lower city center along Wadi Musa would have been devastated, and requiring months to years to remove the massive accumulations of boulders, gravel, sand, silt and clay.

This paper explores Bayesian Markov Chain Monte Carlo (MCMC) methods for evaluation of the posterior distributions of flood quantiles, flood risk, and parameters of both the log-normal and Log-Pearson Type 3 distributions. Bayesian methods allow a richer and more complete representation of large flood records and historical flood information and their uncertainty (particularly measurement and discharge errors) than is computationally convenient with maximum likelihood and moment estimators. Bayesian MCMC provides a computationally attractive and straightforward method to develop a full and complete description of the uncertainty in parameters, quantiles and performance metrics. Examples illustrate limitations of traditional first-order second-moment analyses based upon the Fisher Information matrix.

Sedimentological (dry density, micro-fa-cies analysis on thin-slides, X-ray diffraction, layer counting) and elemental analyses (X-ray fluorescence) of a 3.5-m-long sediment core (MAH-B) from saline Lake Maharlou (SW Iran) were used to infer hydrological changes over the last * 3800 years. The sediment consists of thin, alternating beds of evapor-ites (halite, gypsum), carbonates (calcite, aragonite) and detrital minerals (quartz, muscovite, chlorite). We interpret the data with respect to three main hydrologic conditions: (1) nearly complete desiccation of the lake, marked by frequent halite layers, (2) hypersaline conditions marked by gypsum abundance, (3) wet conditions, characterized by high river-borne terrige-nous sediment input with high potassium content. Distinct flood layers indicate fluvial activity. From about 3800-2000 cal year BP, terrigenous sediment supply was high, with peaks at 3700-3650, 3500-3450, and 3400-3250 cal year BP. Evaporative conditions were not common. From ca. 2000 cal year BP to present, detrital minerals are less abundant, and the increase in gypsum abundance suggests drier climate with enhanced evaporation. Frequent desiccation events occurred from 1100 to 700 cal year BP. The late Holocene hydrology of Lake Maharlou corresponds well with records of dune formation and phases of river alluviation in Iran and the Arabian Peninsula, and with regional speleothem records. In addition to the influence of climate change on the lake hydrology, ancient humans modified water drainage in the catchment. Periods of subterranean tunnel (qanats) use correspond to dramatic shrinkage of the water body. We propose that climate changes drove long-term water shortages that were enhanced by anthro-pogenic activities, leading to more frequent desiccation of the lake during the last millennium.

In international literature, much attention has been paid to sedimentological and geomorphological evidence of extreme floods in the forelands of both contemporary and Pleistocene glaciers and ice sheets. Reports on this subject come from areas and periods of different glaciations. In Poland such events have been documented in more than ten works. This situation prompts us to establish whether or not the occurrence of such extreme events was more frequent and widespread in the area of Poland than it has been believed to date. The article reviews the existing research concerning within the extent of Pleistocene glaciations in Poland, which include the occurrence of high energy glacial outburst floods in the interpretation of sediments or landforms. Its objective is to determine the current state of knowledge and to indicate the direction of further research. The review also includes a study of palaeogeographic conditions of the previously documented jökulhlaup in Siedlątków, on the b...

Glacial deposition and fluvial/lacustrine sedimentation interact over terrains in central New York State to preserve a history of geological and hydrological events as well as hydroclimatic transitions. The lower reach of Fish Creek draining the eastern watershed of Oneida Lake, NY, is an area with prominent wood remains. This study explores a collection of 52 logs encased in organic-rich deposits exposed by bank erosion at three locations along Fish Creek near Sylvan Beach, NY, with respect to radiocarbon ages, species, and the crossdating potential of tree rings. Radiocarbon ages and successful tree-ring crossdating document what we interpret as seven major hydrologic episodes ca. 10 ka (i.e. ca. 10,000 cal yr BP), 7.4 ka, 6.8 ka, 6.4 ka, 5.5 ka, 3.1 ka and 2.2 ka cal BP, during which channel aggradation and tree burial may have been associated with abruptly increased flood frequency and/or high water tables. This pilot study establishes four floating tree-ring records: [1] early Holocene hemlock (Tsuga), mid-Holocene [2] walnut (Juglans sp.) and [3] sycamore (Platanus), and [4] late Holocene elm (Ulmus sp.), with sample sizes of 8–14 series of 55–135 years length. Despite the complexity of distribution of radiocarbon ages at each site, the wealth of well-preserved wood demonstrates great promise for understanding the paleoflood history of the Oneida watershed by documenting the magnitude, location, and timing of floods. Further additional systematic sampling can add and strengthen tree-ring dating and tree-ring based flood records, confirm results, and contribute to the Holocene hydrological history of the region.
Keywords: paleoflood, paleohydrology, riparian forest, U.S. Northeast, Fish Creek, dendro- chronology.

Introduction
The flood is a devastating event that occurs both due to natural causes and due to mismanagement of human factors. During periods of climate change, catastrophic floods have occurred, mainly due to extreme rainfalls, leading to widespread damages and heavy economic losses, displacement, migration, the spread of epidemics, and the mortality of many people. Psychological research related to current global warming also indicates the appearance or exacerbation of mental disorders after the occurrence of this natural event. In this study, the socio-economic and health consequences of floods have been studied, and also, using paleoclimate, archeological, and historical researches, some severe and extensive flood events from prehistory to the present have been presented. Finding reports of flood events from historical documents and discovering evidence of floods among the cultural layers of ancient sites, along with paleoclimate and paleo-flood studies, can yield more accurate results from past climatic and environmental conditions. In the studies of environmental sedimentology of some ancient sites of Iran, evidence of catastrophic floods belonging to the mid-fourth millennium BC has been found and some also have been reported in the historical books of the Islamic period. These events coincide with periods of climate change called medieval warming and the Little Ice Age and occurred mostly in Iran due to extreme rainfalls and flooding of rivers and seasonal streams.
Materials and Methods
In this study, first, the devastating social, economic and health consequences of floods are explained. Then, archaeological evidence is examined, some of which are the result of field research. Finally, historical documents and reports that mention the occurrence of great and influential floods from the early Islamic period to the present are presented.
Results and discussion
Occurrence of heavy rains in a country like Iran, due to its special climatic and topographic features has always caused various natural disasters such as floods and landslides and as a result, has caused great and irreparable economic and social losses (Farajzadeh, 2013: 112). Floods kill more than 2,000 people each year and affect 75,000,000 of the world's population. The reason is the geographical distribution of alluvial fans and shore lines that have long been attractive for human habitation (Mohammadi, 2010: 73).
The occurrence of floods, due to the extreme rainfalls related to climate change, mainly overlapped with drought periods. One of the most important and obvious archeological evidence of floods dates back to the fourth millennium BC. According to the high resolution paleoclimate research of Lake Neor in Ardabil, from about 4200 to 3000 BC, there was a very dry period with increasing dust (Sharifi et al., 2015). During this period, at least two periods of severe drought occurred, 3700-3600 BC and 3250-3150 BC, which are shown by the paleoclimate research of Soreq Cave in the west of Jerusalem (with a resolution of 3 to 20 years) (Bar-Matthews and Ayalon, 2011). Archaeological evidence of floods in the middle and late fourth millennium BC as a result of environmental sedimentology and archaeological excavations in the sites of Mafin Abad Islamshahr, Meymanat Abad Robat Karim and Qara Tepe of Qomroud in North Central Iran, as well as in the sites of Shoruppak, Kish and Ur in Iraq Have been identified (Shaikh Baikloo et al., 2020).
The flood of 628 AD, which occurred due to the flooding of the Tigris and Euphrates rivers in Mesopotamia, was probably one of the main reasons for the fall of the Sassanid dynasty. Blazari, the historian of the Islamic period, in Fotouh Al-Baldan (1958: 414-415), attributes the occurrence of this great flood to the end of the reign of Khosrow Parviz. This event has not only led to the death of many people, but also had more unpleasant consequences such as the destruction of crops, famine, displacement, and the spread of plague.
Conclusion
Therefore, it can be said that if flood prevention and control in Iran are not managed efficiently and effectively, extreme rainfalls related to current climate change (global warming) can cause serious damages and irreparable losses.