5.3 Ecology and flora of Arroyo Alamar

The Arroyo Alamar is part of the Tijuana river watershed. Therefore, its physical and biological characteristics are similar to the majority of the watersheds and river basins located in the northwestern part of Baja California and Southern California. According to the degree of disturbance, the various arroyos which form part of the watershed are divided into three classes:

  • Disturbed in urban areas.

  • Disturbed in suburban areas.

  • Undisturbed in natural areas.

River channelization is accomplished to reduce the risk of catastrophic flooding. However, it reduces riparian habitat, segmenting the local ecology and vegetation. Riparian vegetation is characterized by rapid colonization, high productivity, good dispersion properties, a lowering of species numbers, and a dominance of woody species, specially the willows.

Ecologically, these areas have been classified as riparian, that is, the biological communities that lie along the streams and washes. Biodiversity refers to the variety of biological species and its life forms within an ecosystem. The term "undisturbed" implies a process which significantly alters the patterns of structure and form of an ecosystem, and is usually applied in reference to human activities.

Hydrologic, climatic, and substrate factors determine the composition and, therefore, the structure and function of the riparian vegetation. The riparian ecosystems are protected from strong winds and extreme dry summers. However, this causes the destruction of some vegetation and the creation of new sites for the establishment of new vegetation (Gregory et al., 1991).

From an ecological perspective, the Arroyo Alamar can be divided into three zones:

  1. Zone I, from the concrete channelization to the Cañon del Padre bridge.

  2. Zone II, from the Cañon del Padre bridge to the city of Tecate.

  3. Zone III, from the city of Tecate to its headwaters in eastern San Diego County and the municipality of Tecate.

Zone I lies within the urban limits of the city of Tijuana. It is the most disturbed and polluted of the three zones, and it features many irregular human settlements. The riparian environment and its ecology are heavily impacted by the trash and debris dumps, as well as by stagnant polluted water. It can be divided into three areas:

  1. From the concrete channelization to the Manuel J. Clouthier Boulevard: human settlements, deposits of trash and debris, and polluted surface water. This zone represents a great public health hazard. Several water wells function to provide water for agriculture and recreation.

  2. From Manuel J. Clouthier Boulevard to Terán Terán Boulevard: a few human settlements and trash and debris dumps, stagnant water, mining of sand and gravel, and agriculture.

  3. From the Terán Terán Boulevard to the Cañon del Padre bridge: some trash and debris, brick manufacturing facilities, agriculture and grazing. This is the better preserved area in terms of riparian vegetation (Fig. 19).

Fig. 19  View of Arroyo Alamar immediately downstream of Cañon del Padre bridge.

Zone II shows water pollution from Arroyo Tecate; its vegetation and riparian environments do not show great human impact. Zone III is subject to very little pollution, and its riparian environment is largely unaffected by human activities.

The biological communities are described in terms of their floristic components and their biological forms. The floristic component is assessed by listing all the plants found in a region or area; the biological forms are either trees, shrubs, or grasses. The flora of Arroyo Alamar has a great diversity of native plants and quite a few introduced plants. The latter are characteristic of disturbed environments, principally in Zone I. According to the listings of flora in the official Mexican norm NOM-059-2001, there are no endemic plants, rare plants, or plants in danger of extinction. Table 7 lists the floristic component of Arroyo Alamar.

Table 7.  Floristic component of Arroyo Alamar.
Species Common name (English) Common name (Spanish) Biological form Origin
Ambrosia confertiflora - - grass Nativa
Anemopsis californica [hierba del manzo] hierba del manzo semiaquatic grass Native
Apium graveolens celery ápio aquatic grass Introduced from Eurasia
Arundo donax reed carrizo tall-stem grass Introduced from Europe
Baccharis glutinosa [huatamote ] huatamote shrub Native
Brassica campestris[moztacilla] moztacillagrass Introduced from Europe
Chenopodium murale - - grass Introduced from Europe
Chrysantemum coronarium chrysanthemum crisantemo grass Introduced from Europe
Cotula coronopifolia - - semiaquatic grass Introduced from Africa
Cynodon dactylon [zacate pata de gallo] zacate pata de gallo grass Introduced from Africa
Foenicullum vulgare anise anís grass Introduced from Europe
Helianthemum annum sunflowergirasol grass Introduced from Europe
Heliotropium curassavicum - - grass Introduced from tropical America
Juncus acutus rush junco small shrub Native
Marrubium vulgare [marrubio] marrubio grass Introduced from Europe
Nicotiana glauca [tabaquillo] tabaquillo shrub Introduced from South America
Platanus racemosa alderaliso tree Native
Populus fremontii poplar alamo tree Native
Riccinis comunis [higuerilla] higuerilla small tree Introduced from Europe
Rorripa nasturtium-aquaticum watercress berro aquatic grass Native
Rumex crispus - - grass Introduced from Eurasia
Rumex salicifolius - - grass Native
Salis lasiolepis willow sauce tree Native
Salix goodingii willow sauce tree Native
Scirpus spp. - - grass Native
Solanum spp. - - grass -
Tamarix ramossisima - - tree Introduced from Eurasia
Urtica holosericea [hortiguilla] hortiguilla grass Native
Xanthium strumarium - - grass Native

The climax vegetation of Arroyo Alamar is of riparian corridor type. It is dominated by deciduous trees which help reduce soil erosion and provide habitat for other biological communities.

For many years, ecologists have referred to wide-leaf riparian species such as Populus, Salix, Fraxinus, Platanus and others, as obligatory riparian species. These and other terms such as facultative and pseudoriparian have been applied to diverse riparian species. The U.S. Fish and Wildlife Service has adopted the following terms: "true riparian" for the obligatory riparian, and "pseudoriparian" for the facultative riparian (Reichenbacher, 1984). However, some riparian plants are greatly dependent on the surface water and others on the subsurface water, being quite distinct from the phreatophytes (Smith et al., 1991).

In Zone I, the native vegetation has disappeared almost completely. It was formed by species of trees such as willows (Salix spp.), poplars (Populus fremontii) and alder (Platanus racemosa). These species have almost disappeared, except a few species of willows and a few individuals of poplars and alders along the river banks.

The climax vegetation of this arroyo would be an asociacion of willows and poplars. The willows have a high degree of colonization in Zone I, where it can cover up to 100%. This response of the willows may be due to the large anhropogenic disturbance and to the large deposits of organic matter and nitrate. On the other hand, Zones II and III do not present large populations of these species.

At the present time, the vegetation of Arroyo Alamar in those areas where there is good coverage of vegetation consists of three strata: trees, shrubs, and grasses. In addition, there are also some aquatic and semiaquatic plants.

  • Trees: Dominated first by a type of willow (Salix goodingii) and secondly, by Salix lasiolepis. These are native species, with heights varying from 4 to 15 m, located along the water course and in contact with it.

  • Shrubs: Dominated by two native shrubs, Baccharis glutinosa and Baccharis sarothroides, growing principally outside of the main channel on top of accumulations of sand.

  • Grasses: This strata varies with regard to native and introduced plants, the latter being favored due to the altered environment.

  • Aquatic and semiaquatic plants: Plants which are located in the main channel, under water, or in lagoons in the surroundings..

The most frequent species in aquatic and semiaquatic ecosystems are: Azzola filiculoides, Anemopsis californica, Callitriche orcutti, Cyperus laevigatus, Cyperus lanceolatus, Eleocharis acicularis, Eleocharis geniculata, Eleocharis palustris, Eleocharis parishii, Epilobium adenocaulis var. parishii, Juncus acutus, Juncus bufonius, Juncus sphaerocarpus, Juncus rugulosus, Juncus xiphioides, Lemna trisulca, Lemna valdiviana, Lemna gibba, Lilae subulata, Marsilia fournieri, Mimulus gutatus, Nasturtium officinale, Ophioglossum californicum, Pilularia americana, Ranunuculus cymbaralia, Sagittaria cuneata, Sagittaria greggi, Scirpus acutus, Typha dominguensis, Typha latifolia, Zannichella palustris; besides the introduced reeds Arundo donax and Phragmites australis.

The species Nicotiana glauca) and Salsola kali var. tenuifolia establish themselves quite readily in agricultural and urban areas. Other species occupy areas that have been disturbed; among these are Baccharis sarothroides, Baccharis glutinosa, Erodium cicutarium, Brassica campestris, Haplopappus venetus, Taraxacum officinale, Xanthium strumarium, Ambrosia psilostachya, Cirsium vulgare, Sonchus oleraceus and Datura discolor.

5.4 Design velocities for vegetated and gabion-lined channels

The flow velocity in watercourses has a direct relation to boundary roughness and bank stability. When all other variables are held constant, the boundary roughness decreases as the velocity increases. When the velocity increases, the shear stress increases on the bed and bank material. In turn, this increases the rate of erosion and sediment transport.

There are several ways to protect the stream channel against bed and bank erosion. The bed and banks can be protected directly by using different types of lining, made from both artificial and natural materials. Artificial linings include concrete, gabions, and dumped rock. Natural linings include lawns, vegetated mattresses and bundles of wood.

Table 8 shows a comparison between vegetated and gabion-lined channels.

Table 8. Comparison between vegetated and gabion-lined channels
Vegetated channels Gabion-lined channels
Advantages Disadvantages Advantages Disadvantages

  • Higher infiltration and exfiltration
  • Excellent habitat function
  • Sizable reduction in flow velocity
  • Aesthetically very pleasing

  • Low structural integrity
  • Protection is usually not immediate after installation

  • High stability
  • Moderate infiltration and exfiltration
  • Immediate protection after installation
  • Moderate reduction in flow velocity

  • Less aesthetically pleasing
  • Limited habitat function

Stabilization with gabions

Gabions consist of mesh baskets filled with small riprap. A gabion structure can consist of several baskets (Fig. 2). Since the riprap is enclosed within a wire mesh, it has high stability against erosion. Vegetation can be planted and is able to grow between the gabions layers (Fig. 20). Planting vegetation in gabions provides habitat, decreases the flow velocity during storm events and increases their aesthetic appeal.

Fig. 20 (a)  Woody vegetation in gabions.

Fig. 20 (b)  Woody vegetation in gabions.

Fig. 20 (c)  Growth of woody vegetation in gabions.

Natural bank stabilization

In bank stabilization using natural vegetation, attention must be paid to the temporal wetting zones to assure habitat sustainability. The temporal wetting zones are: (1) Permanently wetted, (2) Intermittently wetted, and (3) Event wetted, or flood plain.

In permanently wetted zones, wattle and fascines are used in various types of assemblies, as shown in Fig. 21. The wattles are staked 30-50 cm into the ground and the stakes are braided with flexible strong brushwood. The height of the wattle assembly is 30-80 cm.

Fig. 21 Wattle assembly for natural bank stabilization.

Fascines can be built as sausages or rolls. The fascine sausages are cylindrical bodies of willow rods with a length of 10-20 m and a diameter of 0.10-0.15 m. They are manufactured from flexible brushwood with a length of 2.5-3.0 m, and anchored with stakes of 4-5 cm thickness and length of about 1 m (Fig. 22).

Fig. 22 (a)  Preparation of fascines.

Fig. 22 (b)  Installation of fascines.

Fig. 22 (c)  Completed fascines.

The fascines rolls are in structure similar to the fascine sausages, with a diameter of 0.25-0.40 m, and 1/3 to 2/3 of their thickness placed under the average baseflow level. Weighted fascines are cylindrical bodies with a diameter of 0.80-1.20 m. They consist of a 0.15-0.20 m thick coat of brush wood and a core of rough gravel or crushed rock (Fig. 23).

Fig. 23 (a)  Weighted fascines.

Fig. 23 (b)  Weighted fascines.

Cattails are placed in the intermittently wetted zone. In the event-wetted zone, the following natural building materials are used: (1) finished lawn, and (2) grass seeding. The lawn pieces are square turf sods with a edge length of 25-30 cm and a thickness of 3-8 cm, imported into place. Lawns are laid flat or in stacks. Flat lawns use bank slopes of 1.5:1-2:1, with 3:1 being rarely used (Fig. 24). Areas with high shear stress should be anchored with stakes of length 20-30 cm. Stacked lawns use bank slopes of 0.75:1 for flowing water bodies and 0.3:1-1:1 at walls (Fig. 25).

Fig. 24 (a)  Flat lawns.

Fig. 24 (b)  Flat lawns.

Fig. 25  Staked lawns.

For lawn rolls, the principle is the same as that of flat lawns. Lawn rolls can be handled over larger surfaces, and they can be grown beforehand on special surfaces.

Fig. 26 (a)  Lawn roll.

Fig. 26 (b)  Installation of lawn roll.

Lawn seeds are disseminated by wet or dry means (Fig. 27). Young seedlings can be protected against removal by means of fiber mattresses or by mixing with a biodegradable adhesive during seeding (Fig. 28).

Fig. 27  Lawn seeding.

Fig. 28  Fiber mattress for protection of seeds.

Vegetative bank stabilization consists of individual components of 2 x 6 m and a thickness of 0.2 m. The materials are a mixture of gravel, plastic mesh, biodegradable geotextiles, and endemic riparian vegetation. The building materials are combined and spread in layers. The assembly can usually withstand large shear stresses (Fig. 29).

Fig. 29  Vegetative bank stabilization.

To stabilize with wood parts, staking woody debris are collected during the winter. These stakes are assembled in one of the following forms: (1) brush mattresses, (2) live staking, and (3) small trees and shrubs. Brush mattresses are anchored to the ground with fascines or wire mesh (Fig. 30). Slopes of 1:1 or flatter may be required to withstand high shear stresses. Water velocities up to 3.5 m/s may be used with brush mattresses.

Fig. 30 (a)  Plan view of brush mattress.

Fig. 30 (b)  Side view of brush mattress.

Live staking uses root-able branch ends with length of 1.0-2.5 m and thickness of 4-6 cm. They are inserted as shown in Fig. 31 (a).

Fig. 31 (a)  Live staking schematic.

Fig. 31 (b)  Live staking soon after installation.

Fig. 31 (c)  Live staking some time after installation.

Fig. 31 (d)  Live staking 2-5 years after installation.

Fig. 31 (e)  Established live staking.

Small trees and shrubs are placed above the baseflow (Fig. 32). They are able to sustain flooding for several days when mature. They are typically used in combination with other measures such as lawn pieces and/or weighted fascines. They provide the following functions:

  1. Stabilization of the bank against erosion.
  2. A mature canopy will provide shading to a good portion of the bank.
  3. Shading reduces the temperature of the water.
  4. For tropical and midlatitudinal climates, this temperature reduction will improve water quality by discouraging the growth of algae and other nuisance species.
  5. This creates a niche habitat for a particular community of flora and fauna.

Fig. 32 (a)  Bank protection with trees and shrubs.

Fig. 32 (b)  Longitudinal view of bank protection with vegetation..

Fig. 32 (c)  Side view of bank protection with vegetation.

Fig. 32 (d)  Completed bank protection with trees and shrubs.

Hydraulic Design

The critical velocity vc and the critical shear stress τc are used in the analysis of the stability of the bottom and the banks of rivers against erosion. The stability can be determined by comparing the actual velocity to the maximum allowable velocity or critical velocity vc based on the bed and bank material.

The Manning equation can be used:

             v = (1/n) R 2/3S 1/2

in which is v = velocity (m/s), n = Manning's n, R = hydraulic radius (m) and S = slope (m/m).

The critical velocity must be determined by experiments or empirically derived from information in the literature. The critical velocity is that at which erosion of the bed and/or bank material begins. The criterion for stability is:

              v <  vc

Typical values of critical velocity are shown in Table 9.

Table 9. Typical values of critical velocity and shear stress
Material Critical velocity Critical shear stress
 (m/s)  (N/m2)
Lawn (short-time loaded) 1.8 20-30
Lawn (long-time loaded) 1.5 15-18
Fascine sausage 2.5-3.0 60-70
Fascine roll 3.0-3.5 100-150
Weighted fascine 2.5-3.0 60-100
Brush mattress 2.5-3.5 150-300
Live staking in riprap   >140
Willows/alder   80-140
Gabions 1.8-6.7 80-140

The critical shear stress τc is a measure of the stability of the bed and banks of a river against erosion. The bottom shear stress can be calculated as follows:

              τo = γ R S

in which is τo = the bottom shear stress (N/m2), γ = specific weight of water (N/m3), R = hydraulic radius (m) and S = slope (m/m).

For wide channels, i.e., those with a top width T ≥ 10 R, the flow depth h is substituted for R:

              τo = γ h S

The critical shear stress τcmust be determined by experiments or empirically derived from information in the literature. The critical shear stress τc is that at which erosion of the bed and/or bank material begins. The criterion for stability is:

              τ <  τc

Typical values of critical shear stress are shown in Table 9.

The variety of vegetation cover available in nature implies that there is also a wide variation in resistance to flow. Flow resistance is dependent on whether vegetation is completely or partially submerged. The controlling factor is the height of the canopy in relation to the water depth. The three general cases are (Fig. 33): (1) short, (2) average, and (3) tall vegetation.

Fig. 33  Short, average, and tall vegetation.

Short vegetation is that which is short in relation to the flow depth, its height being on the same scale as the absolute roughness. The velocity distribution in the cross section resembles that due to absolute roughness. Average vegetation occurs when the plant height is, on the average, the same as the flow depth. It varies between full and partial submersion. The behavior of the resistance to flow demands a special attention to the flow conditions. This is because average vegetation is susceptible to forceful submission (i.e., tilting) when the stream power overcomes the static resistance of the stems. For average vegetation, there is a definite relationship between vegetative resistance and the ratio of plant height to flow depth. Tall vegetation is that which is tall in relation to the flow depth. This definition excludes plants that bend such that their height is decreased below the water surface.

Several examples of roughness coefficients for vegetated channels are shown in Table 10 and Figure 34.

Table 10. Roughness coefficient for vegetated channels.
Surface structure k KSt n
 (m)  (m1/3/s) [Fig. 34]
Lawn 0.06 40 0.025
Grass; field without cover 0.2 30 0.033
Grassland; rocky forest soil 0.25 25 0.040
Grass with shrubs 0.3 24 0.042
Herbaceous vegetation 0.4 22 0.045
Field with arable crop 0.6 21 0.048
Irregular flood plains 0.8 15 0.067
Highly irregular flood plains 1 12 0.083

Fig. 34 (a)  Irregular flood plains: 0.055 ≤ n ≤ 0.083.

Fig. 34 (b)  Herbaceous flood plains: 0.041 ≤ n ≤ 0.050.

Fig. 34 (c)  Grasslands flood plains: 0.028 ≤ n ≤ 0.040.

Fig. 34 (d)  Grasslands flood plains: 0.028 ≤ n ≤ 0.040.

Fig. 34 (e)  Shrub flood plains: 0.028 ≤ n ≤ 0.033.

For conceptually based calculations, the Darcy-Weisbach formula can be used:

       v = (1/ f 1/2) (8 g R S) 1/2    

with

       f = [(4 Ap,i ) / ( ax ay )] cw,i    

for nearly horizontal flood areas, and

       f = [(4 Ap,i cos α) / ( ax ay )] cw,i   

for hillslope flood areas, with

      Ap,i = hi dm,i

The geometric characterization and the equivalent diameter are shown in Fig. 35 and Fig. 36.

Fig. 35  Geometric characterization of tree population density.

Fig. 36  Determination of the equivalent diameter.

For an individual specimen, the coefficient of resistance cw,i is equal to that of a circular cylinder for which cw = 1.2.

For groups of trees or bushes, the following formulas can be used:

              f = [(4 Ap ) / ( ax ay )] cw,r

              f = [(4 Ap cos α) / ( ax ay )] cw,r
with cw,r between 0.6 and 2.4, with mean value cw,r = 1.5.

Riparian Husbandry

Different vegetative species are expected to require different location and flow conditions. All of them are expected to provide vegetative cover to minimize the possibility of channel or bank erosion. For wood, the following practices are recommended:

  • Remove old and sick wood, particularly when they are an obstacle to the flow.
  • With existing vegetation, thin elements positioned in untypical locations.
  • If hydraulically insignificant, leave vegetative debris to encourage habitat (Fig. 37).

Sedges and shrubs should be cut only when hydraulically necessary. For lawns, the following practices are recommended:

  • Mow lawn of embankment once to twice per year.
  • During mowing, attention should be payed to bird eggs.
  • Some areas should be kept unmowed to conserve biodiversity.

Fig. 37 (a)  Examples of vegetative debris.

Fig. 37 (b)  Examples of vegetative debris.

Fig. 37 (c)  Examples of vegetative debris.

5.5 Design of horizontal alignment

The design of the horizontal alignment of Arroyo Alamar has been accomplished following the current location of the streambed. It is understood that the stream will have a tendency to change its alignment with time. The proposed stream rehabilitation fixes the streambed in order to define the external limits of the project.

View of the proposed alignment.

View of the proposed alignment
(large scale): A + B + C + D

View of the proposed alignment: A.

View of the proposed alignment: B.

View of the proposed alignment: C

View of the proposed alignment: D

Fig. 38   Arroyo Alamar:  Detail of horizontal alignment.

5.6 Design of vertical alignment

This document contains an approximate calculation of the volume of granular materials (sand and gravel) that could be extracted from the Arroyo Alamar project if the channel were to be lowered. The rational for lowering the channel has several purposes:

  • To increase the channel conveyance.

  • To extract sand and gravel and commercialize it to support the project development.

  • To enhance the aesthetics of the channel design.

Figure 39 shows the horizontal alignment of the channel design in Arroyo Alamar. A vertical bed-level profile was obtained with AutoCAD, and used to calculate the volume of cut (removal of sand and gravel) from the bed (Fig. 40). Three cases were considered:

  • a. A uniform slope linking upstream and downstream end points (From Puente Cañon del Padre to Primera Etapa del Rio Tijuana).

  • b. A uniform slope at a depth of 1 m below the slope at a.

  • c. A uniform slope at a depth of 2 m below the slope at a.

Fig. 39   Arroyo Alamar:  Horizontal alignment.

Fig. 40   Arroyo Alamar:  Vertical alignment.

The following table summarizes the results of the analysis.

Table 11. Extractable volume of borrow materials from streambed of Arroyo Alamar.
Level
(m)		 Volume
(m3)
-0801,300
-11,575,700
-22,693,400

An analysis has been performed to calculate volumes of sand and gravel mining as a result of rehabilitation of Arroyo Alamar. Results indicate that up to 2.7 million cubic meters can be obtained from the channel bed of Arroyo Alamar by lowering it 2 m.

5.7 Documentation of present conditions

This study has performed a photographic documentation of the present conditions in Arroyo Alamar. Currently, Arroyo Alamar has a mixed use of irregular housing, recreation, light industry, agriculture, gargabe dumps, and other uses. The collection of 108 photographs portray the present conditions in the Arroyo Alamar on September 2002. The rehabilitation will change the look of the channel; therefore, it is necessary to document the present (baseline) conditions to establish the measure to which channel improvements have been accomplished at the conclusion of the project.

Fig. 41   Present conditions in Arroyo Alamar (Click to enlarge and display photos).

6. CONCLUSIONS

The following conclusions are obtained from this study:

  • A hydroecological design has been accomplished for the Arroyo Alamar. The design used the U.S. Army Corps of Engineers' HEC-RAS model to determine design flow depths, mean velocities, Froude numbers, and freeboards for a typical cross-section featuring a compound prismatic channel with left and right overbank side channels (Fig. 3).

  • Gabion systems are a compromise between riprap and concrete channels, and are applicable to the hydroecological rehabilitation of Arroyo Alamar.

  • The ecology and flora of Arroyo Alamar has been described and documented for project use.

  • Vegetative and gabion-lined systems have been documented for project use.

  • Horizontal and vertical design alignments have been accomplished. The use of the streambed of Arroyo Alamar as source of borrow materials (sand mining) has been examined.

  • The present conditions of Arroyo Alamar have been documented for use as baseline data on which to base future assessments of channel rehabilitation and restoration.

  • A website (http://proyectoalamar.org) has been developed to inform interested persons and the public at-large about project developments.

7. RECOMMENDATIONS FOR FURTHER RESEARCH

The following recommendations are offered for further research:

  • Arroyo Alamar should be developed in a sustainable way. For this purpose, the principles of sustainable river architecture should be taken into account. According to this principle, efforts should be made to design the flood plains for soft uses such as recreation, sports education, parking, and so on, following examples already available in Mexico (Atoyac river in Oaxaca and Santa Catarina river in Monterrey).

  • Every effort should be made to discourage, at all levels of government, the implementation of hard solutions such as concrete lining of the flood channel. This type of solution degrades the natural and social environment and negatively impacts a host of other channel uses, such as groundwater replenishment, riparian ecosystem health, biodiversity, and water quality. All over the world, streams and rivers are being restored, to the extent practicable, to their natural conditions. Therefore, any solution based on concrete channelization will represent a serious setback and cause irreparable harm to the local environment.

8. RESEARCH BENEFITS

The following research benefits have been identified:

  • The research has identified a practical and effective way to rehabilitate and restore the Arroyo Alamar following sound hydroecological principles. Over the course of several years, institutional neglect has allowed the Arroyo Alamar to degrade to such a serious state that attention is now of the essence. Currently, Arroyo Alamar is both an eyesore and a public health hazard, not to mention it being a haven for substandard settlements, severe risk of flood damage to life and property, and illegal trash dumping. The focus is currently on the rehabilitation, which will enable Arroyo Alamar to become a green area within Tijuana's city limits, a resource sorely needed for the social and economic well-being of the local population.

  • The research has provided the technical elements to persuade local officials and stakeholders to pursue the Arroyo Alamar rehabilitation along the principles of sustainable development. The research findings specifically discourage any solution based on concrete channelization, and encourages the hydroecological approach to river channelization. The latter is based on sound ecological and social principles, since in this way the river and its natural resources are preserved for the use and enjoyment of the local population, instead of being held hostage (not accessible for use by the local population) through a concrete channelization scheme.

9. ACKNOWLEDGMENTS

The authors wish to acknowledge the assistance of the following persons:

  • Ampar V. Shetty, research associate, San Diego State University.
  • Juan P. Nogues, student, University of Kansas, Lawrence, Kansas.
  • Andreas Koch, student, Magdeburg University, Magdeburg, Germany.
  • Flor Perez Martinez, student, Instituto Politecnico Nacional, Mexico City, Mexico.

10. REFERENCES

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