Hydrological characterization

Data collection

The available mean annual flows are those of the Ain Louali station (figure 15), with the following geographical coordinates (X=555,650m; Y= 377,000m; Z= 245 m), located downstream of the catchment area towards the outlet, these data were obtained on the basis of the monthly values of the flows provided by the Sebou Hydraulic Watershed Agency. The period runs from 1968 to 1970 and from 1979 to 2005, a period of 29 years.
It should be noted that the converting data for the 1970/79 period are absent, to resolve this problem and to ensure data continuity, the values for these nine years have been estimated, following the shape of the flow curve by statistical correlation methods.

Study of the flow rate

Average annual flow

The series of observations thus taken shows that the average annual flow is around 454 l/s. The following figure shows the evolution of annual flows during the period considered(figure 16):
The specific flow or Qsp is a measure of the average flow of precipitation within a river catchment area. It is defined as the number of liters of water that flows on average every second per square kilometer of the basin. Formulation: this is the value of the flow Q (L/s or m3/s) relative to the surface A of the watershed (km2):
Qsp = Q / A
The specific flow is also used to express peak flows during floods. In general, the peak Qsp during floods decreases when the size of the watershed increases.
Specific flow : Qsp = \(1.12\ l/s{/km}^{2}\)
The highest average interannual flow is 1000 l/s recorded in 1969/1970, while the lowest is 300 l/s recorded in 1993/1994 and in 2002/2003.

Average monthly flows

The maximum monthly average flow appears in March (390 l/s), on the other hand the minimum flow is observed in August (325 l/s), the following hydrogram shows the variation of the average monthly flows in Ain Louali (figure 17):
This figure shows that the water concentration requires seven months, from September to March to reach its maximum which represents the peak in March with a value of 390 l/s. The time of the recession begins from the end of March to August, a period of five months to arrive at the minimum quantity of flows. It should be noted that the flood and recession times are approximate since we work with average monthly flows.

Specific flows and height of the flow of water

Many hydrological studies often focus on comparing the hydrological regimes of different stations or streams. It is therefore advantageous to give here the specific flows in l/s/Km² for the period from 68/69 to 2003/04. The specific flow formula:
q = Q / S
The height of the flow of water in mm is given as a function of q which is the specific flow rate (Parade, 1974):
The monthly values of the specific flow rate and the height of the flow of water flow are given in the following table (table 4):
The total volume of water flown is 27.73 mm/year, or approximately 6% of the average volume of water that fell into the watershed (454.22 mm/year). The H/P runoff coefficient (27.73 / 454.22) is 0.061.

Rainfall-discharge relationship

The following table (table 5) shows the monthly flows and precipitation for the period 68/69 to 2004/2005:
When we compare the hydrograph of average monthly flows with that of average monthly precipitation (figure 18), we see that there is a synchronism between flows and monthly precipitation. Indeed, the two curves thus plotted for the same period roughly evolve in the same meaning and in the same way:
In general, the flow of runoff is one of the most important components of the outflow from a hydrological regime fed by precipitation.

Final water balance estimate

The main purpose of any hydrological study is to estimate the water balance of the region concerned, to establish a database corresponding to local water reserves, as well as to guarantee integrated management of these resources. The following table summarizes the results of the Sefrou watershed water balance assessment (table 6):
According to the table (6), the maximum percentage is that of evapotranspiration (87.67%), which can be explained by the high-temperature values during the dry period and by the evolution of the vegetation in the area.
It is important to underline the fundamental points concerning the study carried out under this paragraph. The aspects relating to the hydrology of the Sefrou catchment area bear witness to the Mediterranean hydrological character where the dry season is strongly pronounced. It is therefore obvious to deduce that the hydrological drought has been well marked during the previous 30 years, which has, moreover, been confirmed by the method of differences in the average interannual flow rates.
The study of the hydrological regime using the method of determining the ”precipitation-flow” relationship has made it possible to define a rainfall regime. The mean annual flow is 454 l/s.
The study of the monthly flows shows that there is a similar evolution with a small delay between the maximum values of the flows and the monthly flow coefficients show that the Sefrou catchment area is characterized by an irregular regime. For its part, the study of the specific flows and the height of the runoff water level made it possible to estimate the runoff coefficient which is 0.061.
The water balance showed that the runoff estimation represents 6.06% of total precipitation. As for infiltration, it represents 6.23% of precipitation.
Sefrou watershed provides real water resources and thus ensures the supply of drinking water for the inhabitants of the Middle Atlas regions and more specifically for the habitats of the city of Sefrou. Despite the usefulness of these important capacities, they were causing risks represented by winter floods causing human and material damage, which is solved by the establishment of development projects in the region.