METHOD AND STATION FOR HYDROLOGICAL MONITORING OF A WATERCOURSE

Description

Technical field of the invention

[0001] The invention relates to a method and a station for hydrological monitoring of a watercourse, i.e. a method and a station configured to automatically determine monitoring parameters of a watercourse. Technological background

[0002] The climate change situation that the world is currently experiencing is accompanied by a growing number of hydrological crises (floods, droughts, coastal submersions, etc.) whose consequences, often dramatic for populations, result in part from a lack of knowledge, surveillance and monitoring of surrounding bodies of water.

[0003] Throughout the text, the terms "water bodies" or "watercourses" refer to any body of water, static or dynamic, likely to experience variations in height, speed and / or flow rate depending on climatic conditions. As such, the terminology of "water body" or "watercourse" within the meaning of the invention refers indifferently to rivers, streams, rivers, seas, lakes, ponds, pools, basins of running or stagnant water, etc.

[0004] Solutions already exist for monitoring the evolution of watercourses. For example, patent document CA2961702 describes a system and method for measuring the hydroacoustic parameters of a watercourse using Doppler effect modules associated with imaging systems mounted on observation satellites. This complex set of equipment makes it possible to determine the speed of the watercourse, its depth, etc.

[0005] One of the disadvantages of this solution is the cost of installation and operation, which is not compatible with the monitoring of most watercourses.

[0006] There are also solutions that use submerged sensors, such as velocimeters. These solutions have the disadvantage of being unstable and not very durable over time.

[0007] There are also methods known by the English acronym LSPIV for “Large Scale Particle Image Velocimetry”which allow non-intrusive measurements of the speed of a watercourse from digital images provided by an image acquisition camera arranged in the vicinity of the watercourse. One of the disadvantages of these techniques is that it is necessary to have at least four known reference points in the image to allow a correspondence between a point in the image (defined by its pixel coordinates) and a point in the surrounding space (defined by its longitude, latitude and altitude). In addition, it is necessary to ortho-rectify the images to compensate for the oblique view of the image acquisition camera and then to resize each of the pixels from the known reference points.CN112215903-A describes a river flow velocity detection device with a camera for photographing a river to obtain a first image and a second image and a determination module, configured to determine the movement velocity of a target pixel in the target image based on the first image and the second image and a calculation module for calculating the river flow velocity based on, among other things, the movement velocity of the target pixel.

[0008] In other words, these methods are effective but require GPS points to be taken in the camera's field of view, which has several disadvantages, including access to the banks, which can be difficult (in addition, the presence of an operator equipped with a GPS rod or equivalent means is necessary for calibration); the need to have GPS points that always remain visible in the field of view (a rise in water can make known GPS points unusable); low reliability for low-dynamic watercourses (the speed calculation is based on the observation of a structure that moves from one image to another, which is not very effective for calm bodies of water); etc.

[0009] The inventors sought to develop a method and a hydrological station that overcome at least some of the drawbacks of known solutions. In particular, the inventors sought to propose a method and a hydrological station that allow the monitoring of watercourses using simple, economical, easy-to-install and easy-to-maintain means. Objectives of the invention

[0010] The invention aims to provide a hydrological monitoring station which makes it possible to measure the height of the watercourse and the monitoring speed of the monitored watercourse using simple and inexpensive means.

[0011] The invention aims in particular to provide such a monitoring station which does not require having known GPS reference points.

[0012] The invention also aims to provide, in at least one embodiment, a hydrological monitoring station for a watercourse which can be installed in the vicinity of the monitored watercourse without any particular difficulties by an operator without any particular qualifications.

[0013] The invention also aims to provide, in at least one embodiment, such a monitoring station which can be deployed rapidly on a large number of watercourses and which makes it possible, for example, to instrument the 13,000 watercourses contributing to the risk of flooding in France.

[0014] The invention also aims to provide, in at least one embodiment, a hydrological monitoring station which can be installed in the vicinity of the monitored watercourse for a long period, without requiring regular maintenance.

[0015] The invention also aims to provide, in at least one embodiment, a hydrological monitoring station which has optimized energy management.

[0016] The invention also aims to provide a hydrological monitoring method which has the same advantages as the hydrological station according to the invention. Statement of the invention

[0017] To do this, the invention relates to a hydrological station for monitoring a watercourse comprising: a box equipped with means for attachment to a structure overlooking the watercourse to be monitored, such as a bridge, a lidar housed in said box and oriented vertically towards the watercourse to be monitored, once the box is fixed to said structure, so as to be able to measure the distance between the watercourse to be monitored and said station, a digital camera housed in said box and oriented vertically towards the watercourse to be monitored, once the box is fixed to said structure, so as to be able to acquire images of the watercourse to be monitored, a processing unit housed in said housing and configured to be able to determine the water height directly above the structure on which said station is fixed and the surface speed of said watercourse, from said distance measurement provided by said lidar, from said images acquired by said camera, and from the optical characteristics of said camera, means of wireless communication to a remote server of the monitoring data produced by said processing unit from said water height and said calculated surface speed, a rechargeable battery, housed in said housing so as to be able to supply electricity to said processing unit, said lidar, said camera and said wireless communication means.

[0018] The hydrological monitoring station according to the invention therefore makes it possible to acquire water height measurements and images of the surface of the monitored watercourse without physical interaction with the water surface, to process this data on board the station to deduce monitoring information which is then sent to a remote server, the latter being able to be configured to notify (directly or indirectly) a user of the measurements carried out by the station.

[0019] This user can be of any type and depends on the applications using the data provided by the hydrological station according to the invention. Various uses are possible. For example and without limitation, the hydrological station can be used for the following applications: alert the population surrounding the watercourse of the imminence of a danger (for example a flood) linked to the watercourse, monitor and detect low water levels and droughts, manage water resources (water level of basins, etc.) control hydraulic structures (opening / closing of valves according to the detected water height of a basin for example), validate and calibrate satellite measurements, manage rail traffic on structures likely to be flooded (blocking traffic when a bridge is close to its overflow level), etc.

[0020] The hydrological monitoring station of the invention can be fixed to a structure, such as a point, by means of fixing means associated with a box enclosing the various sensors (lidar, image acquisition camera) and the electronic equipment (control unit, means of communication, rechargeable battery).

[0021] The hydrological monitoring station according to the invention combines the use of a lidar and an image acquisition camera to calculate water height and surface velocity.

[0022] One of the innovative features of the station according to the invention is to use a lidar, not only to measure the height of the water surface, but also to enable the determination of the surface speed. In particular, according to the invention, the lidar and the image acquisition camera cooperate with each other to enable the drawbacks of the LSPIV solutions of the prior art to be resolved, linked in particular to the need to have reference points.

[0023] The hydrological station according to the invention thus makes it possible to determine the surface velocity field of the watercourse from a series of camera shots and lidar height measurements. No reference point is necessary, which greatly facilitates the implementation and installation of a station according to the invention.

[0024] The hydrological station according to the invention is a financially affordable solution (no complex technical means to implement) and flexible (installation, use, maintenance) for monitoring all types of watercourses, opening the way to generalized monitoring of all watercourses in a region, a country and / or a continent.

[0025] Advantageously and according to the invention, said processing unit comprises: a module for calculating the field of vision v observed on the water by said camera, expressed in meters, from the size t of the sensor of said camera, the focal length f of said camera, and the distance d measured by said lidar according to the formula v = t f . d , a surface speed calculation module lives of the watercourse to be monitored, expressed in pixels per second, from said images acquired by said camera, a module for converting the surface speed of the watercourse into meters per second from said speed lives calculated by said speed and field of vision calculation module v calculated by said field of vision calculation module.

[0026] According to this advantageous variant of the invention, the processing unit is configured to calculate the surface speed of the watercourse in meters per second from the images acquired by the camera and from the height information provided by the lidar.

[0027] To do this, the first module (called field of view calculation) uses the height measurement provided by the lidar to calculate the field of view v of the camera expressed in meters according to the indicated equation.

[0028] The second module (called surface velocity calculation) processes the images provided by the camera to calculate the surface velocity expressed in pixels per second. This module advantageously implements an optical flow algorithm which corresponds to the apparent movement of objects, surfaces, contours and edges of a visual scene caused by the relative displacement between the station's fixed camera and the scene formed by the watercourse flowing under the camera.

[0029] The optical flow algorithm seeks to minimize an energy function that corresponds to solving the following equation: dI dx u + dI dy v + dI dt = 0 Or I represents the intensity of a pixel in the image, dI / dxis the gradient of the image along the axis x, dI / dy is the gradient of the image along the axis y, dI / dt is the gradient of the image as a function of time, u and v represent the velocities in the horizontal plane along the respective axes x and y.

[0030] In this equation, the assumption is made that each physical point in the image (not each pixel) retains its intensity during its movement for a short period of time during video capture.

[0031] To solve this equation with two unknowns, it is necessary to make an additional assumption.

[0032] According to the invention, this additional hypothesis is twofold and consists of considering that two consecutive images acquired by the camera are separated by only a short period of time and that the objects have not moved significantly during this short period of time. Indeed, the surface speeds of the monitored watercourses rarely exceed 10 meters per second, i.e. a displacement of 33 cm between images acquired at a frequency of 30 images per second.

[0033] The Farnebäck algorithm allows this additional hypothesis to be materialized by considering for each pixel of the image, a window of NxN pixels which forms the neighborhood of the pixel considered and the hypothesis is made that all the pixels of this window undergo the same displacement as the pixel considered.

[0034] The optical flow equation is then applied to each of the pixels in the window and a polynomial approximation is made for each window, which makes it possible to solve the optical flow equation and know the surface speed expressed in pixels per second.

[0035] The third module (called the conversion module) allows the surface speed of the watercourse to be calculated in meters per second from the said speed lives calculated by the speed and field of vision calculation module v calculated by said field of vision calculation module.

[0036] Throughout the text, a module is a software element, a subset of a software program, which can be compiled separately, either for independent use or for assembly with other modules of a program, or a hardware element, or a combination of a hardware element and a software subroutine. Such a hardware element may include an application-specific integrated circuit (better known by the acronym ASIC for the English term Application-Specific Integrated Circuit) or a programmable logic circuit (better known by the acronym FPGA for the English name Field-Programmable Gate Array ) or a specialized microprocessor circuit (better known by the acronym DSP for the English name Digital Signal Processor) or any equivalent hardware or any combination of the aforementioned hardware. Generally speaking, a module is therefore an element (software and / or hardware) which makes it possible to perform a function, in this case to calculate an output value from input data.

[0037] Advantageously and according to the invention, the station comprises at least two operating modes including: an operating mode, called routine, in which said measurements of water height and surface speed are calculated and sent to said remote server at a first predetermined frequency, an operating mode, called intensive, in which said measurements of water height and surface speed are calculated and sent to said remote server at a second predetermined frequency, higher than said first predetermined frequency.

[0038] According to this advantageous variant, the station optimizes its electrical energy consumption by providing at least two operating modes, including a routine mode and an intensive mode. The routine mode corresponds, for example, to an hourly sending of the average (or median) of 30 seconds of monitoring data measurement and the routine mode corresponds, for example, to a sending of measurement data every 5 / 10 / 15 minutes (at the user's choice).

[0039] Advantageously and according to this variant, the station switches from routine mode to intensive mode as soon as said water height and / or the measured surface speed exceeds a predetermined value.

[0040] This advantageous variant allows for intensifying monitoring as soon as a critical vigilance threshold is reached, which makes it possible to alert the user of the imminence of a critical situation (for example, alerting populations in near real time of the imminence of a flood). This vigilance threshold is set by the user according to the conditions of the monitored watercourse and the targeted reactivity.

[0041] Advantageously and according to the invention, the station further comprises a solar panel connected to said rechargeable battery so as to be able to supply it with electrical energy.

[0042] This advantageous variant makes the station energy-independent and depends solely on solar energy for its operation.

[0043] Advantageously and according to the invention, said means for fixing the box to a structure are removable so as to be able to separate said station from said structure in the event of maintenance.

[0044] This particular aspect of the invention simply allows the station to be fixed or detached from the structure on which it is mounted. Note that if no engineering structure is available above the monitored watercourse, the station according to the invention can also, by means of the removable fixing means, be fixed to another structure comprising an arm allowing the station to be moved above the watercourse to be monitored.

[0045] Advantageously and according to the invention, said removable fixing means comprise magnetic means so as to allow said station to be fixed to a structure with a metal structure.

[0046] This aspect is particularly advantageous for fixing the station to a metal bridge, for example. The removable fixing means can then include a neodymium magnet whose power is determined in relation to the weight of the station.

[0047] The invention also relates to a hydrological monitoring system for a watercourse comprising: a plurality of hydrological stations according to the invention fixed on structures overlooking the watercourse to be monitored, a server for receiving and processing the monitoring data produced by each processing unit of each hydrological station, a notification module configured to emit a notification signal to an external device as soon as said server determines a water height and / or a speed greater than or less than a predetermined threshold requiring a decision from a user.

[0048] The monitoring system includes a notification module (also referred to as "alert" in the text) allowing a user to be notified (directly or indirectly) of measurements from the hydrological station. This user can then make decisions that depend on their use case for the system.

[0049] By way of non-limiting example, this notification module aims to allow the user to carry out the following actions: alert the population surrounding the watercourse of the imminence of a danger (for example a flood) linked to the watercourse, monitor and detect low water levels and droughts, manage water resources (water level of basins, etc.) control hydraulic structures (opening / closing of valves according to the detected water height of a basin for example), validate and calibrate satellite measurements, manage rail traffic on structures likely to be flooded (blocking traffic when a bridge is close to its overflow level), etc.

[0050] The monitoring system according to the invention makes it possible to monitor one or more watercourses simultaneously, each watercourse being equipped with one or more monitoring stations. Monitoring data from several stations in a watercourse can be combined to provide an indication of the dynamics of the evolution.

[0051] The technical advantages and effects of the hydrological station according to the invention apply mutatis mutandis to the monitoring system according to the invention.

[0052] The invention also relates to a method for hydrological monitoring of a watercourse comprising the following steps: measuring by means of a lidar the distance, in a vertical direction, which separates a box housing this lidar and this watercourse, said box being fixed on a structure overlooking said watercourse, acquiring by means of a digital camera housed in said box and oriented vertically towards the watercourse to be monitored, images of said watercourse, determining the water height directly above the structure on which the box is fixed and the surface speed of said watercourse, from said distance measurement provided by said lidar, from said images acquired by said camera, and from the optical characteristics of said camera, transmitting to a remote server monitoring data produced from said water height and said calculated surface speed.

[0053] A method according to the invention advantageously implements a station according to the invention and a station according to the invention is advantageously implemented by a method according to the invention.

[0054] The technical advantages and effects of the hydrological station according to the invention apply mutatis mutandis to the monitoring method according to the invention.

[0055] Advantageously and according to the invention, said step consisting of determining the height and speed of the watercourse comprises: a calculation of the field of vision v observed on the water by said camera, expressed in meters, from the size t of the sensor of said camera, the focal length f of said camera, and the distance d measured by said lidar according to the formula v = t f . d , a calculation of surface speed livesof the watercourse to be monitored, expressed in pixels per second, from said images acquired by said camera, a conversion of the surface speed of the watercourse in meters per second from said speed lives calculated and the field of vision v calculated.

[0056] Advantageously and according to the invention, the calculation of the surface speed lives of the watercourse to be monitored implements the Farnebäck algorithm.

[0057] The invention also relates to a hydrological monitoring station, a monitoring system and a monitoring method characterized in combination by all or part of the features mentioned above or below. List of figures

[0058] Other aims, characteristics and advantages of the invention will appear on reading the following description given solely for non-limiting purposes and which refers to the appended figures in which: [ Fig. 1 ] is a schematic perspective view of a hydrological monitoring station according to one embodiment of the invention mounted on a bridge overlooking a watercourse monitored by the station. [ Fig. 2 ] is a schematic perspective view of a hydrological monitoring station according to one embodiment. [ Fig. 3 ] is a functional schematic view of a hydrological monitoring station according to one embodiment of the invention. Detailed description of an embodiment of the invention

[0059] In the figures, scales and proportions are not strictly respected for the purposes of illustration and clarity. Throughout the detailed description which follows with reference to the figures, unless otherwise indicated, each element of the hydrological monitoring station is described as it is arranged when the station is fixed under a bridge directly above a watercourse to be monitored. This configuration is notably represented on the figure 1.

[0060] Furthermore, identical, similar or analogous elements are designated by the same references in all figures.

[0061] There figure 1 illustrates a bridge 10 which spans a watercourse 11. A hydrological station 20 according to an embodiment of the invention is fixed under an arch of the bridge 10. The hydrological station 20 is fixed under the bridge 10 in such a way that the measuring equipment on board the station (and described later) can have a vertical and perpendicular view of the surface of the watercourse 11. A tolerance of a few degrees (for example 1.5 degrees) is nevertheless permitted without calling into question the measurements carried out by the hydrological station. The hydrological station 20 according to the embodiment of the figure 1 is supplied with electrical energy via a solar panel 15 fixed on the deck and connected to a rechargeable battery housed in the hydrological station.

[0062] There figure 2 illustrates in more detail the hydrological station 20 according to one embodiment of the invention.

[0063] The hydrological station comprises a housing 21 and a fixing plate 22 which supports the housing 21 by means of an arm mounted on a ball joint allowing the orientation of the housing relative to the watercourse. The housing according to the embodiment of the invention has dimensions of 160x80x85 mm. It is made of a material compatible with outdoor installation, such as PVC. Of course, nothing prevents the use of a housing made of another material and having other dimensions.

[0064] The fixing plate 22 is provided with an orifice allowing the passage of screws for fixing the plate to the bridge. Of course, other fixing means are possible within the scope of the claims.

[0065] According to one embodiment, the fixing plate is metallic and the housing carries a magnet allowing it to be fixed to the metal plate by magnetization.

[0066] The housing 21 houses a lidar 23 and a camera 24 for acquiring images of the watercourse 11. The lidar and the camera are fixed in the housing such that their lenses emerge from the housing to point towards the watercourse 11.

[0067] The lidar 23 may be of any known type. As an example and according to one embodiment, it is an infrared lidar with a range of 20m and an accuracy of 1cm at 1Hz. The pulse sending frequency is, for example, 7Hz. Of course, other types of lidar with other technical characteristics can be used without compromising the principle of the invention.

[0068] The image acquisition camera 24 is, according to one embodiment of the invention, a camera equipped with an 8-megapixel infrared sensor. Of course, other types of camera with other technical characteristics can be used without compromising the principle of the invention.

[0069] As shown schematically in the figure 3 , the housing also encloses a processing unit 25 configured to be able to determine the water height and the surface speed of the watercourse, from the height measurement provided by the lidar 23, the images acquired by the camera 24, and the optical characteristics of the camera 24, in particular its focal length and the size of the sensor. The principle of the processing carried out by the processing unit 25 is described later.

[0070] The housing also contains wireless communication means 27 which include, for example, a 4G / 5G chip and a transmitting / receiving antenna. These communication means 27 are intended primarily to transmit monitoring data to a remote server 40.

[0071] Finally, the box includes a rechargeable battery 26 connected on the one hand to the solar panel 15 (not shown on the figure 3 ) and on the other hand to the various elements of the station (lidar, camera, processing unit, means of communication).

[0072] The processing unit 25 comprises, according to one embodiment of the invention, a module 25a for calculating the field of vision v observed on the water by the camera 24, a module 25b for calculating the surface speed of the watercourse expressed in pixels per second and a module 25c for converting the surface speed of the watercourse into meters per second from the speed calculated by the module 25b.

[0073] As previously stated, each module may consist of a software element, a subset of a software program, a hardware element, or a combination of a hardware element and a software subprogram.

[0074] Module 25a calculates the field of vision v observed on the water by camera 24, expressed in meters, from the size t of the sensor, of the focal length f, and distance d measured by the lidar following the formula v = t f . d .

[0075] Module 25b implements the principle of dense optical flow and the Farnebäck algorithm from the images acquired by camera 24.

[0076] As previously stated, the principle of optical flow aims to minimize an energy function which corresponds to solving the following equation: dI dx u + dI dy v + dI dt = 0 Or I represents the intensity of a pixel in the image, dI / dxis the gradient of the image along the axis x, dI / dy is the gradient of the image along the axis y, dI / dt is the gradient of the image as a function of time, u and v represent the velocities in the horizontal plane along the respective axes x And y.

[0077] The Farnebäck algorithm assumes that two consecutive frames in a video are separated by only a time interval dt weak and that the objects did not move significantly during this time.

[0078] Thus, for each pixel in the image, a window of NxN pixels is considered and it is assumed that all pixels in this window have undergone the same displacement. However, since this window is considered for each pixel in the image, several pixels have common neighborhood window parts.

[0079] The optical flow equation is applied to each pixel in the window and then a polynomial approximation is made for each window. The polynomial has the following quadratic form: f x = x T Ax + b T x + c Or A is a symmetric matrix, b a vector, c a scalar, and x is the position of each given pixel in a local frame at the neighborhood window.

[0080] The coefficients of this polynomial are determined using a least-squares estimator with weighting. Thus, by observing how the polynomial transforms under the effect of translation (motion), a method is defined for estimating the displacement fields from the expansion coefficients of the polynomial. After a series of refinements, the optical flow is calculated.

[0081] An interesting feature of Farnebäck's algorithm is that it generates a pyramid of images, where each level has a lower resolution than the previous level. When a pyramid level greater than 1 is selected, the algorithm can track points at multiple resolution levels, starting with the lowest level. Increasing the number of pyramid levels allows the algorithm to handle larger displacements between images.

[0082] The images are processed in pairs. For example, if we consider 5-second video sequences acquired at a rate of 30 frames per second, we obtain 150 images to be processed in pairs. The 149 surface velocity matrices obtained by the algorithm are averaged to provide an average velocity field over the 5 seconds of video. The distance measurement by the lidar is carried out just before the acquisition of the images, for example during the 30 seconds preceding the acquisition of the video sequence.

[0083] The conversion module 25c calculates the surface velocity of the watercourse in meters per second from said velocity calculated in pixels per second by the module 25b and the field of view v calculated by the module 25a. The size of a pixel on the ground is obtained by dividing the calculated field of view by the number of pixels in the image according to the chosen dimension.

[0084] Since the camera is aimed vertically, no perspective correction is necessary. A simple lens distortion correction can be applied to the images.

[0085] The station according to the invention also comprises an energy management module (not shown in the figure 3). This module is configured to switch the station from a first operating mode, called routine, in which the water height and surface speed measurements are calculated and sent to the remote server 40 at a first predetermined frequency (for example one sending per hour) to a second operating mode, called intensive, in which the water height and surface speed measurements are calculated and sent to the remote server 40 at a second predetermined frequency (for example 1 sending every 5 minutes). This energy management module therefore recovers the water height and surface speed measurement information calculated by the processing unit 25.

[0086] The switch from routine mode to intensive mode is carried out as soon as the measured water height and / or surface velocity exceeds a predetermined value which depends on the monitored watercourse. This could, for example, be a water height corresponding to a percentage of its overflow height, this percentage depending on the watercourse and / or the intended application.

[0087] The hydrological station advantageously implements the monitoring method according to the invention which comprises all of the following steps.

[0088] In a first step, the distance, in a vertical direction, between the box housing the lidar and the watercourse is measured using a lidar.

[0089] In a second step, images of the watercourse are acquired using camera 24.

[0090] In a third step, the water height at the level of the structure on which the box is fixed and the surface speed of the watercourse are determined.

[0091] In a fourth step, the monitoring data calculated by the monitoring station are transmitted to a remote server 40.

[0092] The invention also extends to a system for hydrological monitoring of a watercourse comprising a plurality of hydrological stations according to the invention overlooking one or more watercourses to be monitored, a server for receiving and processing the monitoring data produced by each processing unit of each hydrological station, and a notification module configured to emit a signal to an external device (for example a mobile telephone) as soon as the server determines a water height and / or a speed greater than or less than a predetermined threshold.

[0093] The invention is therefore a new, innovative, simple and effective solution for managing hydrological events.

Claims

1. Hydrological monitoring station (20) for monitoring a watercourse (11) comprising: - a housing (21) equipped with means (22) for fixing to a structure positioned over the watercourse to be monitored, such as a bridge, - a lidar device (23) housed in said housing and orientated vertically towards the watercourse (11) to be monitored, once the housing (21) is fixed to said structure, so as to be able to effect a measurement of distance between the watercourse to be monitored and said station, - a digital camera (24) housed in said housing (21) and orientated vertically towards the watercourse (11) to be monitored, once the housing is fixed to said structure, so as to be able to effect the acquisition of images of the watercourse to be monitored, - a processing unit (25) housed in said housing (21) and configured to be able to determine the level of water straight below the structure on which said station is fixed and the surface velocity of said watercourse, from said distance measurement provided by said lidar device (23), from said images acquired by said camera (24), and from the optical characteristics of said camera, - means (27) for wirelessly communicating to a remover server (40) the monitoring data produced by said processing unit (25) from said water level and from said calculated surface velocity, - a rechargeable battery (26), housed in said housing (21) so as to be able to supply electricity to said processing unit, said lidar device, said camera and said wireless communication means.

2. Station as claimed in claim 1, characterised in that said processing unit (25) comprises: - a module (25a) for calculating the field of view v observed on the water by said camera (24), expressed in metres, from the size t of the sensor of said camera, from the focal length f of said camera and from the distance d measured by said lidar device according to the formula v = t f . d, - a module (25b) for calculating the surface velocity vit of the watercourse to be monitored, expressed in pixels per second, from said images acquired by said camera, - a module (25c) for converting the surface velocity of the watercourse in metres per second from said velocity vit calculated by said velocity-calculating module and from the field of view v calculated by said field of view-calculating module.

3. Station as claimed in claim 2, characterised in that said module (25b) for calculating the surface velocity vit of the watercourse to be monitored runs the Farnebäck algorithm.

4. Station as claimed in any one of claims 1 to 3, characterised in that it comprises at least two operating modes including: - an operating mode, referred to as routine operating mode, in which said measurements of the water level and of the surface velocity are calculated and sent to said remote server at a first predetermined frequency, - an operating mode, referred to as intensive operating mode, in which said measurements of the water level and of the surface velocity are calculated and sent to said remote server at a second predetermined frequency, higher than said first predetermined frequency.

5. Station as claimed in claim 4, characterised in that it toggles from the routine mode to the intensive mode when said water level and / or the surface velocity which have been measured exceed a predetermined value.

6. Station as claimed in any one of claims 1 to 5, characterised in that it further comprises a solar panel (15) connected to said rechargeable battery (26) so as to be able to supply it with electrical energy.

7. Station as claimed in any one of claims 1 to 6, characterised in that said means (22) for fixing the housing to a structure are detachable so as to be able to dissociate said station from said structure for maintenance.

8. Station as claimed in claim 7, characterised in that said detachable fixing means comprise means which are magnetised so as to enable the fixing of said station to a structure of metallic construction.

9. Hydrological monitoring system for monitoring a watercourse comprising: - a plurality of hydrological stations (20) as claimed in any one of claims 1 to 8 fixed to structures positioned over the watercourse to be monitored, - a server for reception and processing of the monitoring data produced by each processing unit of each hydrological station, - a notification module configured to emit a notification signal to an external device when said server determines a water level and / or a velocity greater than or less than a predetermined threshold necessitating the user to make a decision.

10. Hydrological monitoring process for monitoring a watercourse (11) comprising the following steps: - measuring by means of a lidar device (23) the distance, in a vertical direction, which separates a housing (21) housing this lidar device and this watercourse (11), said housing being fixed to a structure positioned over said watercourse, - acquiring, by means of a digital camera (24) housed in said housing (21) and orientated vertically towards the watercourse to be monitored, images of said watercourse, - determining the water level straight below the structure on which the housing is fixed and the surface velocity of said watercourse, from said distance measurement provided by said lidar device (23), from said images acquired by said camera (24), and from the optical characteristics of said camera, - transmitting to a remote server (40) monitoring data produced from said water level and said calculated surface velocity.

11. Process as claimed in claim 10, characterised in that said step of determining the level and the velocity of the watercourse comprises: - a calculation of the field of view v observed on the water by said camera, expressed in metres, from the size t of the sensor of said camera, from the focal length f of said camera, and from the distance d measured by said lidar device according to the formula v = t f . d, - a calculation of the surface velocity vit of the watercourse to be monitored, expressed in pixels per second, from said images acquired by said camera, - a conversion of the surface velocity of the watercourse in metres per second from said calculated velocity vit and from the calculated field of view v.

12. Process as claimed in claim 11, characterised in that the calculation of the surface velocity vit of the watercourse to be monitored uses the Farnebäck algorithm.