Methodological Guide to Forensic Hydrology

Abstract

In Latin America and the Caribbean (LAC) region, geophysical, meteorological and hydrological disasters are increasing every year. With significantly limited resources, these countries are naturally forced to absorb lessons from these disasters. One of the fundamental activities during this learning task remains the need to standardize the forensic reporting process. Like all academic disciplines, engineering is exceptional in its application to the forensic field. This feature makes it a unique input to the investigation of hydrological and environmental catastrophes. Based on the fundamental concepts of forensic investigation, ten principles for properly conducting forensic hydrology studies are proposed. The ten principles proposed are: (i) Principle of use, (ii) production, (iii) principle of exchange, (iv) recognition, (v) correspondence, (vi) reconstruction, (vii) principle of probability, (viii) uncertainty, (ix) principle of certainty, and (x) conclusion principle. A hypothetical case of urban infrastructure failure is used to explain, in detail, each of the proposed principles. This paper proposes a methodology to be considered as a reference point for a forensic hydrological analysis to be used at the LAC region.

1. Introduction

The region of Latin America and the Caribbean (LAC) is by nature a zone exposed to extreme events. Floods, earthquakes, droughts, landslides, tropical storms, hurricanes, contamination of aquifers, and others occur in the neighborhoods of cities located in areas exposed to these inevitable disasters. In this LAC region in 2021, geophysical catastrophes made up 22%, meteorological disasters 55%, hydrological disasters 15% and climatological disasters 8% [1]. With significantly limited resources, these countries are forced to absorb the lessons of these disasters, making it necessary to carry out several principles of forensic analysis to recognize the causes of a disaster [2]. The widening of city limits in the LAC region is a consequence of modernity and the need for vital space due to population growth. While this complicated urban development increases the socio–cultural, economic and legal relations of society, it has severe consequences for the potential for disasters [3,4]. The impacts of urbanization on a horizontal (buildings) and vertical (urban plan) land surface cause an increase in impervious areas, the obstruction of natural streams and a decrease in the concentration time of surface runoff [5,6,7]. All these impacts have a significant effect on the increased frequency of urban flooding [8,9]. It is enough evidence to see what happened in the main cities in the LAC region [10,11,12,13,14]. All this urban development and the increase in impervious areas remain the critical problems for storm water management in urban areas [15,16,17]. Studies have proved that the modeling of flash floods in urban areas requires precision in the analysis of precipitation and runoff, especially the spatial and temporal effects [10,18,19,20]. In urban areas, it is the precipitation regime that triggers floods more than any other source of hazards. The regime should understand the magnitude and frequency of an extreme event. In addition, particular interest should be focused on the increase in the frequency of high-intensity and short-duration storms [21]. The key to responding to this is the appropriate management of intervention protocols for an urban environment under rainy seasons, as well as effective hydraulic urban network operational procedures [22,23,24,25,26,27]. This vulnerability of urban areas causes critical material and economic damage due to the flooding of suburban channels, drains, and rivers, affecting fields, urban infrastructure and roads in particular [28,29]. As already mentioned, this is due to the increase in surface flows having too low of a surface infiltration [5]. It is easy to detect the first damage after a severe storm that affects an urban area. Urban debris begin obstructing roads and people and property are quickly affected [30].

Floods, in particular, as extreme events that affect most developing countries, have become exceptionally severe hazards. Most seriously, when it occurs, it causes damage to property and loss of life. However, the most urgent problem is that floods cause significant lags in the progress of the countries of the LAC region [31]. During the last two decades, precise risk management actions have made it possible to reduce this lag [32]. Substantial conceptual improvements support these management actions. Scientific communication and research from disasters unquestionably remain the most critical components of risk management [33]. One of the fundamental activities during this learning task remains the need to standardize the steps to prepare a technical write-up, which can be presented as an environmental crime report [34]. To be specific, post-disaster experience should be used systematically as a learning tool. It is well known that the problem set-up is often more important than its solution. The solution is usually related to a straightforward question of mathematical or experimental skill [35]. Therefore, there is interest in proposing the minimal specifications for the writing of a forensic report.

One of the urgent needs for disaster damage reduction is interdisciplinary research into the root sources of multi-hazard disasters [36]. Like all academic disciplines, engineering takes on an exceptional role in its application in the field of environmental crime and forensic sciences [37]. This feature makes it have a unique contribution to the investigation of hydrological and environmental catastrophes. In these times of catastrophes and disasters, it is necessary to provide scientific knowledge, based on trustworthy and decisive scientific evidence, in the face of an unexpected and increasing risk. Therefore, this work proposes to review these damages through a hydrological–forensic analysis to identify the agents that caused the damage after the event. This hydrological–forensic analysis is based on the traditional criminalistics methods and proposes ten principles to follow to elaborate a hydrological–forensic report, which can be used before a jury to establish or determine responsibilities.

2. Environmental Rights

The United Nations hosted a Conference on Environment and Development in Brazil in 1992. This meeting ratified the United Nations Conference on the Human Environment, promulgated in Stockholm in 1972. The objective was to encourage cooperation, connecting nations and establishing strategic alliances between people and society. Foremost, it was to enter universal agreements to respect, protect and recognize the environment as a developing system [38]. The most representative principle of this initiative is number 15, which reads:

PRINCIPLE 15. To preserve the environment, the Precautionary Approach shall be widely applied by States according to their capabilities. Where there are threats of considerable or irreversible damage, the absence of sufficient scientific certainty should be unused as a reason for deferring cost-effective measures to prevent environmental degradation. This Principle comprises three critical components. (i) The mission to identify the hazard, (ii) risk management and identification of damage, and (iii) the existence of scientific uncertainty.

Thirty years ago, Principle 15 was directly related to the social engagement, which includes providing the authorities in matters of environmental crimes with scientific and technical data. To elaborate a certified report that contains enough elements to characterize the eventual damage produced in the environment. Thus, environmental law must be supported by environmental forensic science to provide evidence and to reach environmental justice, and above all, to technically and economically quantify the damage produced. In this manner, we can say that ecological rights give powers to environmental forensic science to: (i) Carry out scientific research and technically prove the presence of an environmental violation, which may possibly be criminal. (ii) Identify the triggering phenomena of a green crime, its agents, the consequences caused and provide the systematic capacity to reconstruct the facts that caused the suspected crime. (iii) Provide evidence, propose techniques and identification of victims, as required. (iv) Provide sufficient evidence to scientifically verify the degree of active involvement of the suspected offender and others involved.

3. Forensic Hydrology

Forensic science remains an investigation-oriented scientific effort to study traces of previous activities by detecting, recognizing, recovering, examining, and interpreting them to comprehend suspicious events of social interest, like environmental crimes, security incidents or disasters [39]. Criminalistics is one of the fields of forensic science that investigates potential environmental crimes by means of specialized techniques of scientific investigation at the scene. Additionally, it responds to questions about what, who, how, where, why, when and with what. Criminalistics as a forensic science enriches the legal value and use of scientific investigation against illegal activities.

These Forensic Sciences bring together a structured and systemized set of knowledge of a scientific, legal and technical nature, which are applied to the analysis of the facts that are the subject of a judicial conflict [40]. Its study includes disciplines like anthropology, psychology, odontology, voice analysis, forensic medicine, genetics and engineering, and others. Expert specialties provide a valuable contribution to the scientific investigation of environmental crimes from a forensic point of view. The connection between environmental issues and forensic science is materialized in environmental forensic science [41]. In this recently developed area of investigation, the challenge is to expand the boundaries of traditional forensic science to adapt to problems related to environmental damage. To accomplish this goal, it is necessary to employ the knowledge of traditional forensic science to clarify, understand and suggest the reason for the environmental damage that has happened. The modern disciplines that explain, help to acknowledge and instruct us about natural disasters caused by multi-hazard risks include hydraulics and hydrology. In this way, Forensic Hydrology is defined as the methodological scientific study of all hydrological processes involved in and triggering a disaster.

The fundamental objective of Forensic-Hydrology is to reach a chronology and reconstruction of the post-disaster or post-environmental crimes events, based on the properties of the traces and the application of the field and laboratory forensic techniques. It is essential to recognize the focus of the investigation of Forensic-Hydrology begins after a disaster has happened or after an environmental crime has been done. Any analysis prior to a disaster or an environmental crime represents only a hydrological study.

Some of the most common disasters studied by Forensic Hydrology include: Extreme rainfall and runoff, floods, flash floods, mudflows, landslides, catastrophic failures of hydraulic works, overflows of drains, canals and lagoons, fluvial alterations, soil and aquifer contamination, and others.

Examples of environmental crimes associated with hydrology in Mexico include: Discharge of wastewater, chemical or biochemical liquids, wastes or pollutants into soils, subsoil, marine waters, rivers, basins, reservoirs, deposits or federal water streams (Art 416, Federal Penal Code, Mexico, Twenty-fifth Title). Damage to wetlands, swamps, mangroves, lagoons, estuaries, marshes and reefs (Art 420 bis). Destruction of native vegetation; removal or destruction of natural vegetation; cutting, uprooting, felling or cutting down any or some trees, or change in the use of forest land (Art, 418).

3.1. Perfect Research and Contradictions

An environmental disaster or environmental crimes represent a specific type of reduction in the life quality of a human or in the environmental impact in which people live. As a result of a multi-hazard disaster or a social conflict. In both cases, the impact on ecosystems or ecological balance must be evaluated. This implies that the perfect post-disaster or post-environmental crime investigation must always conclude with an environmental evaluation. Environmental services are affected and economic quantification of the damage as the environmental reparation and compensation.

In contrast, there are some conflicting papers in the literature that claim to refer to forensic disaster investigation and Forensic-Hydrology, but they do it in an incorrect sense [42,43], presented what they considered Forensics-Hydrology, however this paper presents only general aspects of what a hydrological study should contain. It does present, in detail, the activities that should be developed “before”, “during” and “after”. However, as already mentioned, the Forensic-Hydrology strictly attends to what happens post-disaster or post-environmental crime. However, these valuable contents can contribute methodological knowledge to hydrological studies. That which is offered as “before” corresponds to “prevention”. That which is presented for “during” is called “immediate response” and is a resilience concept, but it is not a forensic analysis.

The worst case that has been presented in the LAC region is the work reported by [44], called Forensic Investigation of Disasters (FORIN). This is a work that presents an underlying conceptual framework on the social construction of disaster risk. It is very far from bearing any relation to criminalistics or forensic sciences. The most substantial problem is that, in a region so in need of scientific information and trustworthy methodologies, as is the LAC region, such a significant topic is erroneously reported. The evidence is exhibited within the document itself. The authors even acknowledge there was some concern that our use of the term “forensic” was intended to assign fault and provide evaluation of disaster event accounts (p. 26). They later acknowledge FORIN is only a methodology “aimed at disaster risk management” (p. 26).

These two examples represent evidence of the urgent need to propose a consistent scientific methodology associated with forensic science. The objective is to reach the re-creation and post-disaster or post-environmental crime events dating and reconstruction from the properties of the track and the application of forensic techniques in the field and the laboratory [45]. Without a revised and agreed methodology, Forensic Hydrology could end up as malpractice; writing an elementary hydrological study. Forensic Hydrology should be far away from the Daubert case [46]. Forensic Hydrology requires expert researchers, environmental criminologists, rigorous analysis and specific conclusions from the disasters that happen every day in the LAC region. Learning from disasters will contribute to the social development of developing countries [47].

3.2. Fundamentals of Forensic Ethics

From this point forward, it is clear that a group of experts is needed. It is essential to provide a group of experts who have the capacity to justify, defend and demonstrate their post-disaster or post-environmental crime investigation; comply with the necessary criteria that the scientific community considers critical. Such specialists are known as forensic experts. It is significant to remember that, after a disaster or an environmental crime, a Forensic-Hydrology report will be presented to a judicial authority. Therefore, the capacity and ability of an expert witness is an important challenge in the oral confrontation penal system (which at present exists in Mexico). The expert witness needs to develop increased skills and arguments that will allow them to defend in a court of law the Forensic-Hydrology report in a trial. Hence, it can be defined that the expert in Forensic-Hydrology is a person who holds practical, technical and scientific knowledge that uses it to give an opinion and to assist in the administration of justice. The six props support the expert’s activity and are in fact transmitted to the hydrologist’s report; they are known as the ethics of forensic science and are: Legality, objectivity, efficiency, expertise, competence, honesty and respect for human rights [48].

4. Criminalistic Investigation and Its Principles

4.1. The Declaration of Sydney

It is a methodological proposal of excellent scientific standards that describes the essence of forensic science. It comprises a definition of forensic science and seven Fundamental Principles that emphasize the essential role of the trace as a vestige or waste of an investigated activity [39]. These seven principles represent the basis of forensic sciences, which will invariably have as their key objective the construction of truth and legal certainty. Hence, field forensic science uses six of these principles; Laboratory Forensic Science uses three, and Forensic-Hydrology proposes ten core principles. In all cases, the application of these principles belongs to the typical cycle of an investigation (inductive, deductive or analytical) as a systematic approach to develop a vast knowledge of each problem. The seven Principles of the Declaration of Sydney are [39]:

• Activity and presence produce traces that are fundamental vectors of information.
• Scene investigation is a scientific and diagnostic endeavour requiring scientific expertise.
• Forensic science is case-based and reliant on scientific knowledge, investigative methodology and logical reasoning.
• Forensic science is an assessment of findings in context due to time asymmetry.
• Forensic science deals with a continuum of uncertainties.
• Forensic science has multi-dimensional purposes and contributions.
• Forensic science findings acquire meaning in context.

4.2. Field Forensics

This is the research conducted at the scene of an event or where the investigation is taking place. It can be sighted as the origin of the information used for the report. It uses different methodologies and technical procedures to conserve, protect, take advantage of and preserve the investigation site. The prime objective of field forensics comprises the collection and safeguarding of evidence related to the circumstances under investigation, for its subsequent rigorous examination. The principles that it implements are: Principle of production, of exchange, of correspondence, of reconstruction of facts, of probability and the principle of certainty.

4.3. Lab Forensics

This is a study conducted in a controlled environment, like cabinets, laboratories and test areas. The examination of evidence is carried out with the help of instruments, specialized equipment, test prototypes, numerical simulation models, mathematical frameworks, and standardized expert tests. It is known as the detailed part of an investigation and comprises the stage that utilizes the evidence collected in the field to produce conclusive scientific findings [49]. It employs the principles of use, production and certainty as the main concepts [50,51]. For Forensic-Hydrology, the recurrent investigations in laboratory forensics are: Identifying danger zones, height, depths, and velocities of movement, weights and disposition of urban debris. In Forensic-Hydrology, a controlled physical model provides the appropriate instrument to create tests (probabilistic-scenarios) for an experimental analysis of failure or disaster simulation. For example, the rainfall–runoff process that causes severe damage in hydrological basins; at all times, it is desired that these tests could verify the results of mathematical models [52,53].

4.4. Basic Principles of Forensic Investigation

Forensic science has been at the crossroads for over a decade. While this situation represents fruitful ground for debate, the resolution of security problems and the proper administration of justice cannot be deferred. Forensic science must be involved because it is the most reliable way to reconstruct a disaster or environmental crime [54]. We should not only focus on quantifying the uncertainties of our forensic investigations. It should also be called into question the specific ontological nature of forensic science, as a patchwork of disciplines that assist the criminal justice system [55]. This is why it is proposed in this paper to promote the fundamental principles of other forensic disciplines so that they can be accepted and understood.

Hydrology-Forensics therefore aims to remain the basis for collective and interdisciplinary education and research, to learn from environmental disasters and environmental crimes. Research and development in forensic science is currently focused on innovative technologies that improve the efficiency of existing forensic processes [56]. Principles that are not going away and set the foundation are the finding of evidence, scientific investigation and its presentation in judicial proceedings [57]. It is irrefutable that the formalization of the Principles of Criminalistics Investigation for each discipline attend as critical activity; this must be carried out and submitted to the evaluation of collegial, expert and scientific groups.

According to [58], the seven Principles of Criminalistics are similar to those of the Sydney Declaration [39]. However, something fundamental is Locard’s logical reasoning, which today constitutes the keystone of the scientific investigation of crimes [59]. It is equally possible to employ fuzzy logic, geostatistic and stochastic modelization principles for further and more extensive decision-making in forensic hydrology [60,61]. It is substantial to mention that the principles are based on specific questions that researchers, specialists and experts must take into account [62]. While in the forensic science the questions regarding the source of who and what may be different for example from the questions about the activities of where, when, and how. This difference depends completely on the discipline. For example, in medicine, questions about activities may be less crucial [63]. The following is a comparison of the essential questions (basic thinking) that the researcher should ask himself during the process of a criminalistics investigation. Table 1 shows the comparison of the Basic Principles of Criminalistic Investigation.

Table 1. Comparison of the Principles of Criminalistic Investigation adapted from [39,64,65].

Forensic Science Crime	Sydney Declaration	Forensic-Hydrology
		1. Principle of use. During the occurrence of a disaster or environmental crime, the participation of mechanical, physical, chemical, biological, hydraulic, and meteorological. agents is inevitable. These agents must be identified in the initial working hypothesis (Analogical Hypothesis).
	1. Principle of production. The activity and presence of agents produce traces and indications that are fundamental vectors of information, identification and possible reconstruction.	2. Principle of production. Once at least one of the agents has acted, evidence (tracks or marks) is produced. According to the agent represent the evidence, this has an extraordinary etiological significance and scientific properties that support the research.
1. Principle of exchange. The French criminologist Edmund Locard (1910) observed that every criminal leaves a part of him-self at the crime scene and takes something with him. These traces can lead to his identity, since there is inevitably an exchange of evidence between the criminal, the victim and the scene.	1. Principle of exchange. No activities can take place without preserving traces. They are followed or carried away (Locard’s exchange maxim). The nature of the activity influences the types of elements exchanged. The trace represents a vector of information capable of being detected, recovered, examined and interpreted.	3. Principle of exchange. The agent inevitably leaves a trace of his personal identity with the victim and at the scene of a disaster or environmental crime. This recognizes a bi-univocal axiom exchange of evidence. Based on the first two Principles, the exchange hypothesis (inductive hypothesis) is formulated. What could represent the evidence that should be identified or verified in the field?
		4. Principle of recognition. This research will lead to the identification of the cause or agent and the reconstruction of the dynamics of the disaster or environmental crime. It is based on a deductive hypothesis built on verifiable facts.
2. Principle of correspondence of characteristics. There is a logical relationship between the evidence collected at the scene and the probable perpetrator, i.e., they correspond to each other.	2. Principle of correspondence. It is the one that allows deducing, from matching or correlations, the similarity of a trace left by a certain agent or object at the scene of the crime. It is to deduce and to reason under uncertainty, the reconstruction of an event through the study of traces.	5. Principle of correspondence. Based on the first four Principles, it is possible to attribute responsibility for the disaster or environmental crime to at least one of the positively identified agents. The Principle of Correspondence concludes with the identification of the agent or agents who have acted to cause the disaster or environmental crime.
3. Principle of reconstruction. From the evidence collected, the data provided during the investigation and the testimony of witnesses to the event, a realistic reproduction is possible.	3. Principle of reconstruction. Traces represent signs. The formulation of pertinent questions, critical thinking, logical reasoning and the deductive, inductive and analogical process allow the reconstruction of a fact.	6. Principle of reconstruction. The comparative analysis of the identified evidence collected, studied and associated with the disaster or environmental crime provides the qualitative, quantitative and analogical data. That makes possible the systematic reconstruction of the manner in which the disaster or environmental crime occurred.
4. Principle of probability. According to the results acquired in the criminal research. It is possible to determine what represents the probability in which they occurred, and who or who participated in the facts.	4. Principle of probability. No event can be determined with certainty. The circumstances that involve a trace can only evaluate the relative-value of the findings. The quality of the trace could be incomplete, imperfect or degraded. This increases the uncertainty and temporal asymmetry of the findings. It is therefore necessary to evaluate their probability of occurrence in time.	7. Principle of probability. Here begins what is known as the argumentation stage. If the probability $\mathrm{P}\left(\mathrm{x}\right)$ of an event happening is zero $\mathrm{P}\left(\mathrm{x}\right)\approx 0$ means that the event never takes place (falsity). If $\mathrm{P}\left(\mathrm{x}\right)\approx 1$ means that the event always occurs (certainty). At that point, a post-fact hypothesis must be constructed from the most probable facts.
	5. Uncertainty Principle. Forensic science faces with a continuum of doubts that are present at every step of the process. It is necessary to identify and quantify these uncertainties. Subjectivity can be accepted because it is recognized that uncertainty will never be eliminated.	8. Uncertainty principle. There is a theory of untruth. That is, the subjectivity or uncertainty in the verification of facts. At that point a Null hypothesis must be constructed, which refutes the relationship between the facts and explains the uncertainty of the truth.
	6. Principle of certainty. Forensic science has multi-dimensional objectives and contributions. The systematic study of traces makes it possible to establish certainties that recognize the facts and support decision-making in legal proceedings.	9. Principle of certainty. At this stage the hypotheses must be confirmed or rejected. By employing scientific knowledge, the forensic hydrologist obtains results that fall within certitude (certainty). That allows the conclusion that the evidence collected is associated with the participation of agents who acted, in a certain place, to cause the disaster or environmental crimes.
	7. Conclusion Principle. Forensic scientists should defend their findings and opinions as appropriate, while acknowledging any meritorious alternatives.	10. Conclusion principle. A scientific resolution should be presented. The conclusion should answer the questions associated with each stage of the research: detection, localization, chronology, identification and reconstruction (see Table 2). All conclusions should include quantification of uncertainty.

Table 1. Comparison of the Principles of Criminalistic Investigation adapted from [39,64,65].

Forensic Science Crime	Sydney Declaration	Forensic-Hydrology
		1. Principle of use. During the occurrence of a disaster or environmental crime, the participation of mechanical, physical, chemical, biological, hydraulic, and meteorological. agents is inevitable. These agents must be identified in the initial working hypothesis (Analogical Hypothesis).
	1. Principle of production. The activity and presence of agents produce traces and indications that are fundamental vectors of information, identification and possible reconstruction.	2. Principle of production. Once at least one of the agents has acted, evidence (tracks or marks) is produced. According to the agent represent the evidence, this has an extraordinary etiological significance and scientific properties that support the research.
1. Principle of exchange. The French criminologist Edmund Locard (1910) observed that every criminal leaves a part of him-self at the crime scene and takes something with him. These traces can lead to his identity, since there is inevitably an exchange of evidence between the criminal, the victim and the scene.	1. Principle of exchange. No activities can take place without preserving traces. They are followed or carried away (Locard’s exchange maxim). The nature of the activity influences the types of elements exchanged. The trace represents a vector of information capable of being detected, recovered, examined and interpreted.	3. Principle of exchange. The agent inevitably leaves a trace of his personal identity with the victim and at the scene of a disaster or environmental crime. This recognizes a bi-univocal axiom exchange of evidence. Based on the first two Principles, the exchange hypothesis (inductive hypothesis) is formulated. What could represent the evidence that should be identified or verified in the field?
		4. Principle of recognition. This research will lead to the identification of the cause or agent and the reconstruction of the dynamics of the disaster or environmental crime. It is based on a deductive hypothesis built on verifiable facts.
2. Principle of correspondence of characteristics. There is a logical relationship between the evidence collected at the scene and the probable perpetrator, i.e., they correspond to each other.	2. Principle of correspondence. It is the one that allows deducing, from matching or correlations, the similarity of a trace left by a certain agent or object at the scene of the crime. It is to deduce and to reason under uncertainty, the reconstruction of an event through the study of traces.	5. Principle of correspondence. Based on the first four Principles, it is possible to attribute responsibility for the disaster or environmental crime to at least one of the positively identified agents. The Principle of Correspondence concludes with the identification of the agent or agents who have acted to cause the disaster or environmental crime.
3. Principle of reconstruction. From the evidence collected, the data provided during the investigation and the testimony of witnesses to the event, a realistic reproduction is possible.	3. Principle of reconstruction. Traces represent signs. The formulation of pertinent questions, critical thinking, logical reasoning and the deductive, inductive and analogical process allow the reconstruction of a fact.	6. Principle of reconstruction. The comparative analysis of the identified evidence collected, studied and associated with the disaster or environmental crime provides the qualitative, quantitative and analogical data. That makes possible the systematic reconstruction of the manner in which the disaster or environmental crime occurred.
4. Principle of probability. According to the results acquired in the criminal research. It is possible to determine what represents the probability in which they occurred, and who or who participated in the facts.	4. Principle of probability. No event can be determined with certainty. The circumstances that involve a trace can only evaluate the relative-value of the findings. The quality of the trace could be incomplete, imperfect or degraded. This increases the uncertainty and temporal asymmetry of the findings. It is therefore necessary to evaluate their probability of occurrence in time.	7. Principle of probability. Here begins what is known as the argumentation stage. If the probability $\mathrm{P}\left(\mathrm{x}\right)$ of an event happening is zero $\mathrm{P}\left(\mathrm{x}\right)\approx 0$ means that the event never takes place (falsity). If $\mathrm{P}\left(\mathrm{x}\right)\approx 1$ means that the event always occurs (certainty). At that point, a post-fact hypothesis must be constructed from the most probable facts.
	5. Uncertainty Principle. Forensic science faces with a continuum of doubts that are present at every step of the process. It is necessary to identify and quantify these uncertainties. Subjectivity can be accepted because it is recognized that uncertainty will never be eliminated.	8. Uncertainty principle. There is a theory of untruth. That is, the subjectivity or uncertainty in the verification of facts. At that point a Null hypothesis must be constructed, which refutes the relationship between the facts and explains the uncertainty of the truth.
	6. Principle of certainty. Forensic science has multi-dimensional objectives and contributions. The systematic study of traces makes it possible to establish certainties that recognize the facts and support decision-making in legal proceedings.	9. Principle of certainty. At this stage the hypotheses must be confirmed or rejected. By employing scientific knowledge, the forensic hydrologist obtains results that fall within certitude (certainty). That allows the conclusion that the evidence collected is associated with the participation of agents who acted, in a certain place, to cause the disaster or environmental crimes.
	7. Conclusion Principle. Forensic scientists should defend their findings and opinions as appropriate, while acknowledging any meritorious alternatives.	10. Conclusion principle. A scientific resolution should be presented. The conclusion should answer the questions associated with each stage of the research: detection, localization, chronology, identification and reconstruction (see Table 2). All conclusions should include quantification of uncertainty.

Table 2. Example of questions that can be asked in forensic science, medicine and Forensic-Hydrology (adapted from [63]).

Type of Information	Forensic Science	Medicine	Forensic Hydrology
Detection	Did a crime happen? What are the relevant trace(s) that can be detected?	Is a person suffering from a health problem? What are the relevant symptom(s) that can be detected?	Has a disaster, environmental crime or environmental damage happened? Who or what caused the event? What effects did the event cause? (Direct and indirect).
Localization	Where is the trace(s) at the scene?	Where is the symptom(s) on/in the human body?	Where did the event happen or was it triggered? What agent(s) caused the event? Why did the incident happen? What are the relevant evidences about the event?
Chronology	When were the traces generated and in which sequence?	When did the symptoms first appear, and how did they evolve?	When did the disaster, environmental crime, or damage occur? When did it happen?
Identification	Who/what is the source of a trace?	What is the source of a symptom?	What evidence should be collected and preserved in relation to the event?
Reconstruction	What activities may have caused the generation of the traces?	What activities/lifestyle may be contributing to the observed symptom(s)?	Why are the events treated as a disaster, an environmental crime or damage to the environment?

Table 2. Example of questions that can be asked in forensic science, medicine and Forensic-Hydrology (adapted from [63]).

Type of Information	Forensic Science	Medicine	Forensic Hydrology
Detection	Did a crime happen? What are the relevant trace(s) that can be detected?	Is a person suffering from a health problem? What are the relevant symptom(s) that can be detected?	Has a disaster, environmental crime or environmental damage happened? Who or what caused the event? What effects did the event cause? (Direct and indirect).
Localization	Where is the trace(s) at the scene?	Where is the symptom(s) on/in the human body?	Where did the event happen or was it triggered? What agent(s) caused the event? Why did the incident happen? What are the relevant evidences about the event?
Chronology	When were the traces generated and in which sequence?	When did the symptoms first appear, and how did they evolve?	When did the disaster, environmental crime, or damage occur? When did it happen?
Identification	Who/what is the source of a trace?	What is the source of a symptom?	What evidence should be collected and preserved in relation to the event?
Reconstruction	What activities may have caused the generation of the traces?	What activities/lifestyle may be contributing to the observed symptom(s)?	Why are the events treated as a disaster, an environmental crime or damage to the environment?

5. Decalogue of Forensic-Hydrology and Its Application

Consider a hypothetical case to explain the ten Principles of Forensic-Hydrology. After a storm in August 2014 [10], a brick-wall collapsed in a residential area close to a river (urban drainage). The collapse of this wall caused losses and damage, and for this reason Hydrology-Forensic is requested to provide technical expertise. The river has its origin in the high watershed in exceedingly typical conditions, i.e., without urbanization. In the natural watershed, the stream has a natural channel with a bottom and banks of soil and vegetation; a river with curves subject to overflowing (Figure 1a). In the middle of the watershed, the river flows through crop fields and some farms (Figure 1b). In this zone the flow is conducted through channels covered with brickwork, rock-fill and native vegetation. Downstream of the watershed is the urban zone (the place where the wall falls). Within this urban zone, the stream flows through drains (channels) made of brickwork or with a concrete covering. Through the whole surface flow along the river, several hydraulic works, flow control elements and all the functional components of the river can be found. For example, floodgates, urban infrastructure, bridges, culverts, confluences with other watercourses (Figure 2a), secondary discharge pipes over the drain (Figure 2b). With this information, the next proposed principles are to carry out the scientific research, which are illustrated.

5.1. Principle of Use

The procedure starts with the recognition of a cognizant subject. Hydrologist-Forensic scientist and a declared object: Disaster or environmental crime scene. At the beginning of an investigation, it is essential to formulate a hypothesis (working/initial hypothesis), which will be improved as the research progresses. It should be an Analogical Hypothesis that recognizes the participation of mechanical, physical, hydrological, hydraulic and meteorological agents in this case.

Initial hypothesis: The extreme rainfall (hydrological agent) caused the over-rise in the river level (hydraulic agent) (Figure 3). The river overflowed its natural course. Some element coming from the stream impacted the wall and triggered the failure.

5.2. Principle of Production

It is already certain that at least one of the agents was engaged (Figure 4). It is associated with that evidence, and traces or tracks are produced. Finding these marks will allow for the reconstruction of the disaster or environmental crime. The marks or signs must be documented in space and time.

5.3. Principle of Exchange

Some evidence of flooding is found in the river, in the buildings and in the functional components of the river. In this case, urban debris was found. In Figure 5a, urban debris such as tree branches and trash deposited in a storm drain overpass. In Figure 5b, debris on the branches of a downed tree allows us to determine the possible height of the water level reached.

At this point it is possible to modify the hypothesis and propose the Exchange Hypothesis.

Exchange hypothesis: The extreme rainfall, the accumulation of garbage and urban debris, could have reduced the hydraulic capacity of the channels and drains. This caused an over-elevation in the river level. The river overflowed its banks. The urban debris carried by the flow could have hit the wall and caused the collapse.

5.4. Recognition Principle

At this point, it has been identified that some of the urban debris was relocated by the force of the water. It traveled through the channel and eventually hit the wall. This hypothesis helps in the reconstruction of the dynamics of the disaster or environmental crime. This can be seen from the ground walks and the evidence that can be seen in Figure 6a,b. The hypothesis changes to a Deductive Hypothesis. At that point, it seems faithful to assume it was a rock. This means that near the failed wall, rocks should be found. However, it is substantial to consider that, if it was not a rock, then it had to be only the force of the flow. This will have to be demonstrated.

Deductive hypothesis: Extreme rainfall, accumulation of garbage and urban debris reduced the hydraulic capacity of the riverbeds and drains. This caused an over-elevation in the river level. The river in most of its course flowed out of its banks, but in some places the river bottom and banks were eroded. Rocks were flushed away by the flow and could have hit the wall and caused it to collapse.

5.5. Principle of Correspondence

At this point, based on the exchange of evidence, the impact of rocks on the wall is probable. However, the Principle of Correspondence requires assigning the authorship of the disaster to at least one of the fully recognized agents. For this reason, all evidence must be investigated in detail [66]. Upstream of the disaster area a culvert has been blocked by the construction of an interior wall in a very negligent manner (Figure 7). This causes a decrease in the hydraulic area in the culvert. Looking at Figure 7a before flooding and Figure 7b, it is steady to deduce that only rocks with diameters of less than 0.45 m were able to pass through the culvert. This size of rocks is not capable of knocking down a brick-wall. This evidence points to the force of the water as the exclusive agent involved in the disaster.

5.6. Reconstruction Principle

The comparative analysis of the identified evidence collected studied and associated with the disaster or environmental crime provide the qualitative, quantitative and analogical data that make possible the systematic reconstruction of the way in which the disaster or environmental crime occurred. At this phase, it is critical to engage experts in the required specialties. All the evidence collected, the data provided during the investigation and the testimonies of those who witnessed the events are used. In this way, it is viable to reconstruct the events as closely as possible to what in fact happened. An appropriate reconstruction makes it possible to deduce and recreate how the catastrophe or environmental crime occurred. Reconstruction activities can be carried out in the field or the laboratory. The research carried out at the scene of the events is known as field forensics. When it is necessary to manipulate instruments, specialized equipment, models, experiments and all somewhat modern reconstruction techniques and mathematical tools, it is called laboratory forensics. This Principle of Reconstruction is the one that requires the most meticulous detail in the investigation. This stage enables us to move from hypotheses (suspicions) to conclusions (exactitudes).

For our example case, it is necessary to use a controlled discharge channel adapted for Forensic Hydrology studies. This channel consists of a three-meter-long riprap zone, which is equivalent to a debris drag of 60 m (Figure 8a). Moreover, it has a storage tank of 2.1 m³ of water that can be discharged directly by an instantaneous operation gate (flash-flow). To simulate the collapse of a brick-wall, dynamic–geometric scaling is calculated to determine the height of the equivalent wall in the channel (Figure 8b). In this way, a failure of the brick-wall can be induced. The collapse of the wall and the debris propagation allow for the failure to be recreated successfully. The scene is enhanced with the support of sonic sensors and videos taken in slow motion. The sensors provide information on water levels, and consequently, the energy with which the water hit the wall. Additionally, soil erosion simulators (Figure 8c) or flow meters for curves in channels or rivers (Figure 8d) can be used. These are just a few examples of the equipment and physical models that can be used in the Reconstruction Principle stage.

For this particular case, a surface channel (forensic hydraulics channel) and an instantaneous opening gate are used. It is equipped to make possible a flash opening capable of triggering a crash wave. This channel allowed for recreating urban flood failures. Similarity analyses are performed to scale the dimensions of real hydraulic works. Sonic sensors are additionally provided to monitor water levels. The specifications of this channel are shown in Appendix A.

5.7. Principle of Probability

At this point, it is certain that is was the force of the water hitting the wall that caused it to fail. There is certainty that rocks transited the channel, but they could not strike the wall because they could not pass through the culvert (Figure 7). From hydrometric records, it is associated with the historical flows that run through the river (Appendix B). Currently, with this information it is necessary to understand the probability associated with this runoff. This procedure is known as Frequency and Risk Failure Analysis.

If the probability $\mathrm{P}\left(\mathrm{x}\right)$ of an event occurring is zero, $\mathrm{P}\left(\mathrm{x}\right)\approx 0$ means that the event never happens (falsehood). $\mathrm{P}\left(\mathrm{x}\right)\approx 1$ means that the event always happens (certainty). Furthermore, a post-fact hypothesis must be constructed from the most probable facts. When historical records of a phenomenon are used, defined as hydrological data, they should be assigned a return period according to their frequency of occurrence (frequency table). To calculate it, it is assumed that the frequency or interval of recurrence of each observed event allows for assigning a return period to each data. This is known as the empirical return period. Since the return period has a completely probabilistic definition, in its mathematical form Tr of a hydrological event x, it should be defined as the inverse of the probability P(x) of that event x to occur. This means that the probability of being equalized or exceeded by another event x must be expressed as:

$${\mathrm{T}}_{\mathrm{r}}=\frac{1}{\mathrm{P}\left(\mathrm{x}\right)}=\frac{1}{\mathrm{P}\left(\mathrm{X}\ge \mathrm{x}\right)}$$

(1)

If a certain event has a return period of 25 years, then an event probability of 1/25 = 0.04 is defined. This should be interpreted as the probability that the event will be matched or exceeded in any one year. It is important to mention, for example, that a return period of 25 years does not mean that the event is presented every 25 years; what it means is that it will be presented on average over a 25 year time span. For the design of any hydraulic work, the event must be calculated for an empirical return period using a frequency table as shown in

Table 3. Definition of the empirical return period and probability of occurrence [67].

Order Number m	Observed Value	Return Period Tr (Years)	Probability of Occurrence
1	x1	n + 1	1/(n + 1)
2	x2	(n + 1)/2	2/(n + 1)
m	xm	(n + 1)/m	m/(n + 1)
n − 1	xn−1	(n + 1)/(n − 1)	(n − 1)/(n + 1)
n	xn	(n + 1)/n	n/(n + 1)

. The following is the construction of an empirical frequency table to calculate the empirical return period and the probability of occurrence of a historical database. The historical values of the event under study should be ordered from highest lowest. An order number m is assigned, up to the total value of historical data (n). The results for our example-case are reported in

Table A2. Frequency analysis. Historical flow data in m³/s for the proposed example river.

Year	Flow	Ordered Event	Order	Return Period (Year)	Probability of Occurrence
1993	1660.0	3800.0	1	30.00	0.03
1994	618.0	2280.0	2	15.00	0.07
1995	876.0	1660.0	3	10.00	0.10
1996	563.0	1410.0	4	7.50	0.13
1997	824.0	1230.0	5	6.00	0.17
1998	557.0	1150.0	6	5.00	0.20
1999	917.0	1120.0	7	4.29	0.23
2000	683.0	1030.0	8	3.75	0.27
2001	740.0	934.0	9	3.33	0.30
2002	520.0	921.0	10	3.00	0.33
2003	824.0	917.0	11	2.73	0.37
2004	818.0	876.0	12	2.50	0.40
2005	3800.0	824.0	13	2.31	0.43
2006	934.0	824.0	14	2.14	0.47
2007	1120.0	818.0	15	2.00	0.50
2008	360.0	779.0	16	1.88	0.53
2009	1230.0	740.0	17	1.76	0.57
2010	1030.0	683.0	18	1.67	0.60
2011	1410.0	658.0	19	1.58	0.63
2012	779.0	618.0	20	1.50	0.67
2013	610.0	610.0	21	1.43	0.70
2014	1150.0	581.0	22	1.36	0.73
2015	522.0	563.0	23	1.30	0.77
2016	418.0	557.0	24	1.25	0.80
2017	2280.0	522.0	25	1.20	0.83
2018	921.0	520.0	26	1.15	0.87
2019	367.0	418.0	27	1.11	0.90
2020	658.0	367.0	28	1.07	0.93
2021	581.0	360.0	29	1.03	0.97

in Appendix B. The results of the Probability Principle suggest that in August 2014, the maximum annual event recorded was 1150 m³/s with the order number equal to 6. A return period of 5 years and a probability of occurrence of 0.20.

5.8. Uncertainty Principle

To assign a probability of occurrence (level of damage) to a catastrophic event remains an excellent practice in environmental forensics [68]. However, it is desirable to eliminate, as much as possible, the subjectivity or uncertainty in the ascertainment of the facts. Since Forensic Hydrology is associated with the failure of infrastructure and hydraulic works, it is critical to estimate not only the probability of occurrence. However, it must be transformed into a potential risk of failure [69]. This is possible by taking into consideration the relationship between the probability of occurrence of a hydrological event, the useful life (service life) of the work being designed and the risk of admissible failure. The latter depends on economic, social and technical factors. Setting a risk of failure is something that must be done a priori considering the risk to be assumed by the event that the work should fail within their lifetime, which implies that an event of magnitude greater than that used in the design of the work during the first, second, third year of operation, and so on for each of the years of the work’s useful life does not occur. This is why the probability of failure of the hydraulic work for its useful life of n years must be calculated. From the nomenclature used in Section 5.7, you can define the probability of no-exceedance (non-occurrence) of a hydrological event in any one year as: $1-\mathrm{P}\left(\mathrm{x}\right)$, the probability of no-exceedance in two consecutive years will therefore: ${\left[1-\mathrm{P}\left(\mathrm{x}\right)\right]}^2$. The probability of no-exceedance in three consecutive years is: ${\left[1-\mathrm{P}\left(\mathrm{x}\right)\right]}^3$ and the probability of no-exceedance in N consecutive years will be: ${\left[1-\mathrm{P}\left(\mathrm{x}\right)\right]}^{\mathrm{N}}$. Then, the probability of exceedance in N consecutive years will complement the latter expression. Thus, the probability of the occurrence of an event return period Tr over a period of N years is known as the failure risk due to rainfall and flows-flood. It is also used to calculate the probability of occurrence of a debris-flow during a period of N years [70,71]. Could be calculated as:

$$\mathrm{R}=1-{\left[1-\mathrm{P}\left(\mathrm{x}\right)\right]}^{\mathrm{N}}$$

The failure risk can be expressed as a function of the return period:

$$\mathrm{R}=1-{\left(1-\frac{1}{{\mathrm{T}}_{\mathrm{r}}}\right)}^{\mathrm{N}}$$

(2)

where R is the risk of failure within the useful life of the hydraulic-civil work or the probability of the occurrence of a debris-flow. N is the number of years of the useful life of the hydraulic-civil work or the occurrence period of a debris-flow.

Suppose that a hydraulic work with a useful life estimated as 10 years is designed or exposed to an event with a return period of 20 years. The risk or probability of failure will represent 40% [67]. In all cases, it will be the owner of the civil work that must define the reasonable risk of failure and the useful life of the civil works.

The example case. Looking at Table A2 for the year 2014 when the extreme event that collapsed the wall happened, the maximum flow in the river was 1150 m³/s. As already mentioned in Section 5.7, the probability of occurrence of this event represents 20%. If we consider that a brick-wall supports a useful life of up to 50 years, the house where the failure occurred attends only 10 years old. This implies that the brick-wall was still within the time lag of its useful life. It is substantial to mention that the older a civil work is, the higher the probability of failure, due to the natural deterioration of the materials over time. The risk of failure is then calculated. In Equation (2), using the return period equal to five years and taking into account a useful life of the brick-wall of 10 years at the time of collapse, R = 0.8926%. This means that the probability of occurrence of this maximum flow in the river represents 20%, but the risk of failure of a brick-wall subjected to this event with a life of 10 years is 89%. It is substantial to emphasize that it has not yet been demonstrated with what force the water hit the wall. That is, if the maximum flow of the river caused the collapse.

5.9. Principle of Certainty

At this stage, by exploiting scientific knowledge, the forensic hydrologist obtains outcomes that achieve a substantial degree of precision (certainty). Various configurations of brick-walls within forensic hydraulics channel were tested and collapsed. From these results, it is possible to have certainty about the magnitude and frequency with which the agents were involved in causing the disaster. It is crucial to mention that the results presented below are the consequence of real tests carried out in the laboratory. The force (F) of the water necessary to collapse the bricks-wall in a time of 2.8 s in the model (forensic hydraulics channel) is equivalent to 41.18 Newtons. It is important to remark that this value was obtained with the water level of 0.4 m and with the same brick placement for the creation of the wall. This has the support of a geometric and dynamic scaling procedure. From the values obtained in the model, it is associated with the full scale; the brick-wall was impacted by an effective force of F = 1112.48 kN provided by a flow equivalent to $302.17{\mathrm{m}}^3/\mathrm{s}$. The collapse of the wall occurred in an estimated time of 15.33 s after the impact. Figure 9 shows the results of the brick-wall failure induced in the forensic hydraulics channel (Figure 9a) and the image of the collapse that in fact happened (Figure 9b).

5.10. Conclusion Principle

A scientific conclusion must be presented. The conclusion should answer the questions associated with each stage of the investigation: Detection, localization, chronology, identification and reconstruction (see Table 2). All conclusions should include uncertainty quantification [72]. If, for some reason, the forensic hydrologist attach conditions that do not guarantee the certainty of the results, it is necessary to request secondary data and work with a more extensive amount of material evidence to deepen, and systematic the study or at least; to mention the uncertainty in reaching a conclusion [73].

From Blong’s work (2003) [74], it is clear in saying that damages must be quantified. If probability and risk are evaluated in the forensic analysis process, the magnitude must be judged by the forensic hydrologist and thus dictate this conclusion. Damage scales may be nominal (categorical), ordinal, interval or ratio scales. Frequency words such as “few”, “many” can be dealt with in a range of ways to produce contiguous, widely separated, broadly overlapping or narrow overlapping values. Most scales rely on maximum values but some focus on minimum or threshold values. Blong (2003) and Balica (2012) [16,74] present an exhaustive review of damage scales and vulnerability factors for a vast range of events, such as: Earthquakes, winds, tropical cyclones, tornado, hailstorm, hail, tsunami, landslide, subsidence, volcanic eruption, volcanic ash, geomagnetic storms, asteroids and comets, rain rates [28] and others. Table 4 shows the substantial capacity to recognize some associations of extreme events that could produce damage. To characterize the agents that act and cause damage or a disaster, it is of substantial importance to define the concept of the regime. The regime should be understood as the simultaneous definition of magnitude and frequency. That is to say, by knowing the regime of an event, we will be characterizing it. Each process of the hydrological cycle and every action of the disaster cycle has magnitude and frequency. A valuable practice of the forensic hydrologist is properly to define, as far as possible, the regime of the agent involved in the disaster or environmental crime.

As demonstrated, a forensic hydrologist must always document the magnitude and identify the frequency. For example, during a flood in an urban area, water runs off with a velocity between 2.5 and 5 m/s. For every 0.5 m that the water rises, the lateral force on a normal vehicle is approximately 250 kg (2450 N). In this situation, the vehicle would weigh 680 kg less. Therefore, a stream of water 0.5 m depth can carry away most automobiles. To know a risk factor in urban areas, it is conventional to multiply the speed and depth of the water [75]. With respect to pedestrians, an adult of medium size will be in risk in a flooded street; with a water depth of only 0.2 m and a flow velocity of 2 m/s [76].

Table 5. Damage hazards scales and factors classification suggested for the LAC region [9,15,23,26,28,29,74,75,76,79,80,81].

Damage State-Factor Range [Damage or Risk]	Rain Rate R (mm h−1) [Rainfall Height hp] (mm 24 h−1)	Hazard Flow–Velocity (m s−1) [Landslide Velocity]	Hazard Flow Depth y (m) [Flood Duration]	Jointly Flow Depth y (m) and Flow Velocity v (m s−1)	Safe for … [Expected Damage]
Slight-very slow (0–1) [1%]	$\text{<5}$  $\text{<5}$	$\text{<5}$  $\left[16 \mathrm{mm}/\mathrm{year}\right]$	$\text{<0.2}$  $[\text{<6 h}]$	$y<0.5$ & $v<15$	All save [Not damage]
Light-low-slow (1–10) [5%]	$5\le \mathrm{R}<20$  $5\le {\mathrm{hp}}_{24}<20$	$0.5\le \mathrm{v}<1$  $\left[1.6 \mathrm{m}/\mathrm{year}\right]$	$0.2\le y<0.5$  $\left[\text{6–12} \mathrm{h}\right]$	$0.5\le y<1$ & $v<3$	Cars and able bodied adults [Water and sediment-laden water ingresses building’s main floor or basement]
Moderate-medium (10–30) [20%]	$20\le \mathrm{R}<30$  $20\le {\mathrm{hp}}_{24}<50$	1$\le \mathrm{v}<2$  $\left[13 \mathrm{m}/\mathrm{month}\right]$	$0.5\le y<0.8$ $[\text{12–18} \mathrm{h}$]	1$\le y<1.5$& $v<2$	Heavy vehicles and wading for adults [Lost related to wet furniture and some supporting elements damaged]
Heavy-high-fast (30–60) [45%]	$30\le \mathrm{R}<50$  $50\le {\mathrm{hp}}_{24}<70$	$2\le \mathrm{v}<3$  $\left[1.8 \mathrm{m}/\mathrm{hour}\right]$	$0.8\le y<1$  $\left[\text{18–24} \mathrm{h}\right]$	$1.5 \le y<2$& $v<1.5$	Light constructions [Furniture wet, broken windows and doors are reported]
Major-very high-very fast (60–100) [80%]	$50\le \mathrm{R}<70$  $70\le {\mathrm{hp}}_{24}<150$	$3\le \mathrm{v}<4$  $\left[3 \mathrm{m}/\min \right]$	$1\le y<1.5$  $\left[\text{24–48} \mathrm{h}\right]$	$2\le y<3$ & $v<3$	Heavy constructions [Everything get wet and damage to crucial building-supporting piles and walls]
Destroyed-extreme-extremely fast (100) [100%]	$\mathrm{R}\ge 70$  ${\mathrm{hp}}_{24}\ge 150$	$>4$  $\left[5 \mathrm{m}/\mathrm{s}\right]$	$y>1.5$  $[\text{>48 h}]$	$y>3$ & $v>3$	Nothing [Structure is completely damaged or destroyed]

presents a review of the key magnitudes of extreme events related to Forensic Hydrology.

Table 4. Risk and hazard analysis of the principal agents involved in Forensic Hydrology.

Agent, Dimensions and Usual Units	Regimen	Estimated and Required Action for Hazard Analysis
Flow and flood 1  $\frac{{\mathrm{L}}^3}{\mathrm{T}}=\frac{{\mathrm{m}}^3}{\mathrm{s}}$	$\mathrm{Flow} \mathrm{rate}=\frac{\mathrm{water} \mathrm{volume}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Flood water depth (y)
		Flood duration
		Flood water velocity (v)
		Water sedimentation
		Return period of flow (${\mathrm{T}}_{\mathrm{r}}$)
Rainfall and hailstorm 2  $\frac{\mathrm{L}}{\mathrm{T}}=\frac{\mathrm{mm}}{\mathrm{h}}$	$\mathrm{Rainfall} \mathrm{rate}=\frac{\mathrm{rainfall} \mathrm{height}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Rainfall height (hp)
		Rainfall height in 24 h (${\mathrm{hp}}_{24}$)
		Rain rate also known as precipitation intensity (R)
		IDF curves magnitude-duration-frequency
		Return period of rainfall (${\mathrm{T}}_{\mathrm{r}}$)
Debris and debris-flow 3  $\frac{{\mathrm{L}}^3}{\mathrm{T}}=\frac{{\mathrm{m}}^3}{\mathrm{s}}$	$\mathrm{Debris} \mathrm{rate}=\frac{\mathrm{production} \mathrm{volume}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Debris flow hazard recognition
		Estimation of debris flow probability
		Regimen production of debris flow (volume and frequency)
		Volume of the initiating failure
		Volumes entrained along the transport reach
		Estimation of volumes deposited along the transport reach
Landslide 4  $\frac{\mathrm{L}}{\mathrm{T}}=\frac{\mathrm{m}}{\mathrm{month}}$	$\mathrm{Landslide} \mathrm{rate}=\frac{\mathrm{distance}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Landslide type (by origin) and height
		Landslide direction / movement type
		Landslide velocity
		Landslide impact pressure and soil material

Note(s): ¹ Physical flood vulnerability indicators-weighted in [26]. ² Physical Parameterization of IDF Curves based on short-duration storms in [21]. ³ Suggested debris-flow magnitude classifications in [70]. ⁴ A proposed classification of the landslide process and impacts in [77,78].

Table 4. Risk and hazard analysis of the principal agents involved in Forensic Hydrology.

Agent, Dimensions and Usual Units	Regimen	Estimated and Required Action for Hazard Analysis
Flow and flood 1  $\frac{{\mathrm{L}}^3}{\mathrm{T}}=\frac{{\mathrm{m}}^3}{\mathrm{s}}$	$\mathrm{Flow} \mathrm{rate}=\frac{\mathrm{water} \mathrm{volume}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Flood water depth (y)
		Flood duration
		Flood water velocity (v)
		Water sedimentation
		Return period of flow (${\mathrm{T}}_{\mathrm{r}}$)
Rainfall and hailstorm 2  $\frac{\mathrm{L}}{\mathrm{T}}=\frac{\mathrm{mm}}{\mathrm{h}}$	$\mathrm{Rainfall} \mathrm{rate}=\frac{\mathrm{rainfall} \mathrm{height}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Rainfall height (hp)
		Rainfall height in 24 h (${\mathrm{hp}}_{24}$)
		Rain rate also known as precipitation intensity (R)
		IDF curves magnitude-duration-frequency
		Return period of rainfall (${\mathrm{T}}_{\mathrm{r}}$)
Debris and debris-flow 3  $\frac{{\mathrm{L}}^3}{\mathrm{T}}=\frac{{\mathrm{m}}^3}{\mathrm{s}}$	$\mathrm{Debris} \mathrm{rate}=\frac{\mathrm{production} \mathrm{volume}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Debris flow hazard recognition
		Estimation of debris flow probability
		Regimen production of debris flow (volume and frequency)
		Volume of the initiating failure
		Volumes entrained along the transport reach
		Estimation of volumes deposited along the transport reach
Landslide 4  $\frac{\mathrm{L}}{\mathrm{T}}=\frac{\mathrm{m}}{\mathrm{month}}$	$\mathrm{Landslide} \mathrm{rate}=\frac{\mathrm{distance}}{\mathrm{frequency} \left(\mathrm{time}\right)}$	Landslide type (by origin) and height
		Landslide direction / movement type
		Landslide velocity
		Landslide impact pressure and soil material

Note(s): ¹ Physical flood vulnerability indicators-weighted in [26]. ² Physical Parameterization of IDF Curves based on short-duration storms in [21]. ³ Suggested debris-flow magnitude classifications in [70]. ⁴ A proposed classification of the landslide process and impacts in [77,78].

6. Discussion

Additionally information is not only significantly valuable, but also the opinion of other experts [82]. Investigations are a team effort requiring the informed input of laboratory personnel and other experts when making investigative decisions [83,84]. Even Traiuman (2019) [84] mentions that there are an increasing demand from the community on the accuracy and detail of findings in forensic investigations. At present, the demand for evidence and conclusions about environmental crimes and incidents has been influenced even by television series. Society, the audience and especially the victims expect better and more detailed conclusions. Even if we turn to what people see on a day-to-day TV series like CSI (Crime Scene Investigation), and NCIS (Naval Criminal Investigative Service), appropriate answers are required [85]. Fortunately, for us, TV shows have advanced since the time of Telly Savalas as Kojak. Now, NCIS-Gibbs Rule #8 advises us: Never take anything for granted. In any event, the work of the forensic hydrologist must be adequate and must allow learning from the disaster. This is most important for countries critically damaged by disasters, as is the case in the LAC region. For our case example, it is concluded that the river overflowed and it was the force of the water that damaged the brick wall. A video of a segment of the test carried out in the forensic channel is presented in the Supplementary Materials. The probability of occurrence of this event represents 20%. The risk of failure of a brick-wall subjected to this event with a life of 10 years is 89%.

Learning from catastrophes is one of the most critical actions for developing countries, especially in the LAC region. Their economic and social development is significantly limited and the disasters that increase year by year do not contribute to the improvement of their conditions. Our countries are significantly affected by extreme events and disasters that are scarcely analyzed [86]. Currently, there is no valid methodology to carry out a forensic analysis on the subject of hydrology. A technical document or a paper submitted and published in a scientific journal represents an essential step forward for the countries of the LAC region. This methodology can provide a learning process and a key reference document to understand, carry out reconstruction and recognize the facts that happen after a disaster [87]. In any event, it is critical to criminally safeguard the environment [88,89]. Environmental Law is insufficient to prevent the depredation of ecosystems [90]. The mediate or ultimate purpose, which is the most important from the social point of view; consist of providing the appropriate authorities with the scientific and technical data conducive to the exercise of the criminal action. Therefore, supporting the hard and noble mission of the administration of justice [91]. To conclude it is important to mention that Forensic Hydrology remains a dynamic process that does not end and that invariably establishes current evidence to learn. Finally, we can paraphrase on NCIS-Gibbs Rule #3: Never believe what you are told; double check.

7. Conclusions

This paper presents the methodology of Forensic Hydrology as a proposal for the reconstruction and explanation of facts related to hydraulics and hydrology. Man is degrading the natural environment at an ever-increasing rate. Criminal law must remain the latter line of environmental protection. It is the responsibility reflected in the following actions: Precaution, prevention, damage, repair, compensation and economic sanction. Forensic Hydrology includes a double idea: A proximate or primary objective and an ultimate or mediate purpose. The primary or proximate purpose is to determine the existence of an incident presumed to remain an environmental crime or reconstruct it. Alternatively, it is to establish or point out the intervention of one or several subjects in the incident. Independent reviews of unsolved cases can help identify missed leads, unidentified forensic potential of evidence, and other issues. However, these reviews must be concluded by qualified individuals with the support of the investigative agency. Practical recommendations take into account an agency’s capabilities, resources, and proper limitations.