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Procedia Environmental Science,

Engineering and Management

http://www.procedia-esem.eu

Procedia Environmental Science, Engineering and Management, 4 (2017) (4) 283-290

International Symposium on Soil and Water Bioengineering in a Changing Climate, 7th-8th September, 2017, Glasgow, Scotland, UK

RESTORATION PROJECT FOR STREAMS

AND BANKS OF LA SAÚCA CREEK, MADRID, SPAIN*

Isaac Sanz, José L. García, José C. Robredo

Escuela Técnica Superior de Ingeniería de Montes, Forestal y del Medio Natural. Campus Ciudad Universitaria Avda. de la Moreras s/n, 28040 Madrid, Spain

Abstract The main aim of this project is to perform a hydrological study and for proposing necessary actions against erosive processes and incision at the channel and the banks in the basin La Saúca Creek, located in the municipality Alameda del Valle, Madrid, Spain. In order to identify the hydrological dynamic of the stream, the existing information on the current state of the basin was analyzed, as well as the flows of the basin to assess its torrential hydraulic. Finally, a specialized software was applied to complete a flooding study. The incision processes, which configured deeper transversal section and a smaller width/deep coefficient, became very unfavorable and a stream concentration and bigger stream velocity were induced. The causes of the incision problems can be grouped by human and/or cattle origin. HEC-RAS and Geo-RAS software were used to model possible floods in the stream close to the village. Additionally, HEC-HMS was used for estimate peak flows. The flood risk results of the study zone showed that tiny floods could be produced in short periods of 5 and 10 years flood. The aim was to propose actions for controlling those floods and to stop the incision processes. After the completion of the hydrological study and the analysis of the incision and erosion problems, a series of actions were proposed to correct the incision and the erosion of the banks and the channel. The main objectives of the actions proposed in this project were: (i) to stop erosion and incision processes by stabilizing slopes and banks; (ii) to restore the riparian forest through afforestation. Bioengineering techniques proposed were a combination of Rock rolls and Fiber rolls with GeoCells for bank stabilization and latterly an afforestation of the riparian forest with autochthonous species. Finally, the restorations were protected for the wildlife and the cattle by fences. Key words: Riverbank restoration, floods, technics bioengineering

Selection and peer-review under responsibility of the ECOMED project consortium Corresponding author: e-mail: [email protected]

Sanz et al./Procedia Environmental Science, Engineering and Management, 4, 2017, 4, 283-290

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1. Introduction Sauca Creek is a seasonal watercourse that crosses the town of Alameda del Valle (Madrid). At the entrance of the village crosses the M-604 road and continues until it flows 1 km downstream on the Lozoya River. Some corrective measures have been implemented in the channel during its passage through the municipality based on the dredging of the solid material transported by the stream, but these dredges have not solved the erosive problems of the watercourse. The reach as it passes through the urban center of Alameda del Valle, presents a situation that is briefly described below (Simon and Rinaldi, 2006): The riverbanks of the channel have undergone processes of incision in the bed and steep

slopes in the last years due to floods. On the last avenue (Fig. 1), the transport of solid materials caused a clogging of a natural

dam, which caused the stream to find an alternative outlet to the Lozoya River, crossing mown meadows, with the damage it caused to its owners.

The current riparian vegetation is scarce and hardly influences the support of the banks of the channel.

Fig 1. Alameda Torrent in a flood the last winter

2. Objectives The area is located in the NW region of the Community of Madrid within the Alto del

Lozoya Valley, belonging to the Tagus River Basin (Gómez, 2016). The municipality is in the region of the Sierra de Guadarrama. The study area comprises the lowest area of the basin. The entire surface that drains to La Sauca Creek has a basin of 1,504.37 ha and a perimeter of 19.83 km. The total length of the stream is 8.580 m and that of the section of the basin under study is 1,380 m in the La Sauca Creek and 356 m in the stream of La Zarza Creek. The highest altitude is 2,169 m and the lowest point at 1,100.5 m in the river Lozoya. The stream of La Saúca is presented as a typical Mediterranean mountain stream with a width varying from 3 to 5 m, of a rectilinear type, maintaining discharge throughout the year except summer. The stream runs downstream with an elevated slope collecting flows from smaller streams until arriving at the piedmont where the slope is softened. This situation of high slope generates the transport of materials that, dragged by the water, produce a

Pure oxygen-based MSW bio-stabilization: preliminary results of a full scale investigation

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remarkable erosion in the riverbanks of the channel and bed facilitating the dragging of the loose materials.

These effects are causing incisions in the bed and the banks of the channel as it passes through the urban center of Alameda del Valle. In addition, there have been landslides in zones with strong slopes putting in risk the stability of one of the streets of the town parallel to the channel. Erosion of the linear bed tends to increase the height of the riverbanks, specifically in the parts where the soil is more susceptible to erosion. The scouring produced at the base of the slopes cause collapses and the widening of the cross-sectional width.

On the other hand, the channel of the main tributary, La Zarza creek, in its lower part crosses a prairie that formed part of the floodplain of the river Lozoya and that after a construction of a hillock was isolated of the influence of Lozoya River. However the bed of La Zarza is very little marked due to the greater seasonal character and together with a negligible slope a few meters before the mouth to Sauca the altitude is slightly lower than this one, The river floods the entire surrounding area and in flood episodes and can affect the streets and buildings nearby.

3. Basin hydrological study 3.1. Analysis of extreme precipitation

The calculation of the hydrological parameters is done using two different methodologies in order to be able to evaluate the results, one is the estimation of runoff flows with the Curve Number method and the Rational method and another is the application of the HEC-HMS software to a storm type. The Rational equation is the simplest method to determine peak discharge from drainage basin runoff. Once the maximum precipitation for the series has been calculated with the Gumbel distribution, the different return periods are calculated, the Curve Number for each land use are obtained and the Rational method is applied for a type storm (Fig. 2) with the De Salas (2004) law (Eq. 1):

(1)

Fig. 2. Hyetograph of storm of 50 year flood


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3.2. Rational method

Rational method assumes a series of basic hypotheses as that the precipitation is equal throughout the surface of the basin and that the intensity of this is constant, at least during the time of concentration. 3.3 Analysis of solid discharge 3.3.1. Method U.S.L.E.

USLE model is applied the in all watershed (Fig. 3) with the Roldan et al (2004) law to the erosivity index in this watershed as given by Eq. (2).

R annual = 177.70 hJ/m2ꞏcm/h (2)

The highest value of erosion occur in the circus and glacial moraine areas located at the headcut of the basin. Likewise, high values are also found in the riverbanks of the lower cross sections of the main channel, which is why this project is carried out, as well as in urban areas.

Fig. 3. Map of erosion 3.3.2. M.U.S.L.E. method

This model allows to make a calculation of the sediments emitted by the basin for a concrete storm (Table 1). The model is very known (Roldán et al., 2009). The law is given by Eq. (3).

SLPCKQV.Y .p 560811 (3)

where: Y is de sediment supply in a storm (t/storm); V is the runoff volume (m3); Qp is a peak flow (m3/s); K is erodibility factor (tꞏmꞏh/haꞏJꞏcm); LxS is topographic factor; C is a land use factor; P is a practices of soil conservation.

The values obtained are excessive in comparison with reality, since they use the


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starting hypothesis of unlimited erosion and deposition. In Table 2 the quantities estimated for a return period of 100 years flood trough HEC-HMS are shown.

Table 1. Peak discharges and runoffs

Return

Period (yr) Pmax 24 h

(mm) Ptc (mm)

Peak flow Qp(m3/s)

Run off Q (mm)

Run off Q (m3)

2 54.81 18.83 0.12 0.02 262.48 5 70.62 24.44 6.20 0.17 2629.39 10 81.11 27.87 11.39 0.55 8266.56 20 91.14 31.32 17.23 1.12 16778.64 25 94.33 32.42 19.25 1.33 20034.03 50 104.14 35.79 25.93 2.10 31607.12

Table 2. Sediment supply of a 100 year flood

T (yr) E (mm) V (m3) Qp (m3/s) Y (t/storm) Y (t/haꞏstorm) 100 2.10 45308.16 33.23 12917.59 8.59

4. Materials and methods 4.1. Assessment of peak flow with HEC-HMS software

The hydrological simulation using the unit hydrograph method is carried out with the HEC-HMS. This software estimates the flow rates at critic cross sections as outlet in the sub-basins and delimited micro-basins using a type diagram of an extraordinary event of 6 hours duration calculated using the De Salas (2004) method and the SCS Storm option, developed by the USCS which provides the program

Fig. 4. Peak flow of 100yr return period (HEC-HMS). 4.1. Flood study by HEC-RAS

The simulation of a flood is carried out with the HEC-RAS. This software allows the calculation of the profile of the water sheet of a river section for one-dimensional stationary movement. It allows to perform calculations for different types of hydraulic regime. From the data of previously calculated peak flows and the sections calculated by a topographic


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survey, the flooding study is carried out (Fig. 5). In addition, a mixed regime has been considered.

The results on the flood risk of this study show that small floods could occur in return periods of 5 and 10 years floods For higher return periods the heights of the water sheet would be higher and would be detrimental in the areas closest to the channels.

Fig. 5. Map of cross-sections and result of one of them

4.2. Incision on La Saúca Creek channel In the lower section of the basin, the incision processes are important in the channel,

forming transverse sections that are ever deeper and with a smaller width / depth coefficient, becoming very large (Figs. 6, 7). This change of the section determines a concentration of the flow and an increase of the speed of the waters, gradually lowering the base level, which reduces the water table of the banks and the frequency of its flood, being disconnected from the operation of the river (Darby and Simon, 1999). A channel with problems of incision has problems of vertical instability and imbalances. The height of the slopes increases until the failure of the slope occurs and the channel begins to widen.

The discharge capacity increases and the channel is capable of progressively transporting larger volumes of water within its section. In this case, the currents are restricted to the section and exert a strong shear stress transporting more sediment which can cause serious problems in the channel and in the shores near the town.

5. Slope stabilization and actions in riverbanks

The actions that have been designed can be summarized as: Regulation of the bed of the channel and remodeling the some riverbanks to contain the

advance of the incision of the stream. Revegetation of riverbanks through riparian reforestation with autochthonous material. Stabilization of riverbanks. Improvement in livestock monitoring in areas near river.


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All actions that involve changes in the terrain and fixation and stabilization of slopes will be carried out using bioengineering techniques to avoid, as far as possible denaturalizing the channels.

Fig. 6. Comparison of the channel in the 1990s and today where you can see how the incision process concentrates the channel in deeper sections. Author: Isaac Sanz

Fig. 7. Incision on a riverbank 5.1. Slope stabilization

At the base of slope is proposed a line of flexible gabions based on stones and ridges of site on which the vegetal rolls are mounted (Fig. 4) will be placed and all this is fixed by the installation of poles of treated wood. In this way, a certain protection of the edge and the base of the slope of the erosive processes is obtained. As the soil depth is minimal, formed by large blocks and alluvial ridges, the rest of the slope will be protected by the installation of a framework of geocells. 5.2. Actions in riverbanks

The proposed solution is to slightly modify the river banks by installing flexible gabions based on stones and ridges of the place so that the bases of both banks along the river are paved and protected along the river as it passes through the town. To finish off the


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action, the upper part is protected from erosion by the installation of fiber rolls (Fig. 4) where they will insert cuttings of the species Salix spp. and Populus spp.

Fig.4. Fiber roll and Rock roll (Magdaleno, 2011)

5.3. Riverbanks reforestation

Reforestation of this cross section will be carried out following a broad plantation framework that does not pose future problems with the extraordinary events and the peak flows that can occur. The objective is to complement the previous action giving a vegetation cover to the banks and zones closer to the channel.

6. Conclusions

Bioengineering allows to apply multiple techniques to solve the same problem. In this project we have opted for the solutions described in this article seeking a balance between the functionality of the solutions, their ease of application and their final price.

With the evident problems of incision in the channel and in the banks, the priority actions have been to stop this process as quickly as possible and later to recover the riparian vegetation through reforestation.

References Darby S.E., Simon A., (1999), Incised River Channels: Processes, Forms, Engineering, and

Management, John Wiley and Sons, New York. De Salas L., (2004), Regionalization of IDF laws for the use of hydrometeorological flow estimation

models, On line at: http://oa.upm.es/168/. Gómez M., (2016), Estudio hidrológico de la cuenca de cabecera del río Lozoya a su paso por

Alameda del Valle, Madrid, PFC. Escuela Técnica Superior de Ingenieros de Montes, UPM, Madrid, Spain.

Magdaleno F., (2011), Manual of Fluvial Restoration Techniques, Ministry of Public Works, Secretary of State for Infrastructure Planning, Publications Center, Spanish.

Roldán M., Carrero L., Gómez V., (2009), Estimation of the R factor of monthly and annual rainfall erosivity with monthly and annual precipitation data respectively, On line at: https://www.researchgate.net/profile/Juan_Perez_Arango/publication/216513501_Estimacion_del_factor_de_erosividad_de_la_lluvia_en_Colombia/links/09e4150ac0b265ab41000000/Estimacion-del-factor-de-erosividad-de-la-lluvia-en-Colombia.pdf

Simon A., Rinaldi R., (2006), Disturbance, stream incision, and channel evolution: The roles of excess transport capacity and boundary materials in controlling channel response, Geomorphology, 79, 361-383.

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