_____________________________________________________________________________

TRIP REPORT Mocorito River Basin and SantaMaria Bay Sinaloa, Mexico

_____________________________________________________________________________

Irlbeck, Michael J

2002

Citation:U.S. Bureau of Reclamation, Austin, TX

For more information contact: Pamela Rubinoff, Coastal Resources Center, Graduate School ofOceanography, University of Rhode Island. 220 South Ferry Road, Narragansett, RI 02882Telephone: 401.874.6224 Fax: 401.789.4670 Email: rubi@gso.uri.edu

This five year project aims to conserve critical coastal resources in Mexico by building capacity of NGOs,Universities, communities and other key public and private stakeholders to promote an integratedapproach to participatory coastal management and enhanced decision-making. This publication was madepossible through support provided by the U.S. Agency for International Development’s Office ofEnvironment and Natural Resources Bureau for Economic Growth, Agriculture and Trade under the termsof Cooperative Agreement No. PCE-A-00-95-0030-05.

TRIP REPORT

Mocorito River BasinandSanta Maria BaySinaloa, Mexico

May 2, 2002

2

Summary

The purpose of this report is to provide a cursory, watershed perspective of the mostsignificant water-related issues in the Mocorito River and Santa Maria Bay, Sinaloa,Mexico. It is based upon the author’s personal observations during an 8-day trip to theregion and from his discussions, meetings and direct inquiries with various localindividuals. After general background information is provided about the State ofSinaloa, a description of the Mocorito River basin is presented. Included is a summary ofthe observed alterations of the watershed resulting from a variety of human activities.

In the subsequent section, the primary human values of water resources in the basin(namely, agriculture, coastal fishery and municipal uses) are discussed, and the principalthreats to these values identified. Identified threats to agriculture use include thecompromised production of agricultural land. Threats to coastal fishery use includeunregulated harvest pressure on shrimp resources, current operation of Buelna Dam andreservoir, future diversions from the Mocorito River, contamination of freshwater inflowto the estuary, and an altered sedimentation rate into the bay. The threats to municipaluse include public health risks from lack of water sanitation and chemical contaminationof source water. In addition, a summary of Conservation International-Mexico’s (CI-Mex) strategy for addressing threats to water resources in the region is also discussed.

The report ends with the conclusion that although the important water resources of theState of Sinaloa are threatened by various human activities, CI-Mex’s community-basedapproach appears to be reasonable and effective in better understanding the presentthreats and in developing and implementing potentially viable solutions.

3

Outline

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Purpose and Scope of the TripReport ObjectiveOverview of Sinaloa

OBSERVATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5The Mocorito River Basin

The Upper BasinThe Coastal PlainsThe Estuary

Human Alterations in the Mocorito River BasinThe Upper BasinThe Coastal Plains

Agriculture PracticeMunicipal Use

The EstuaryIntensification of the Shrimp IndustryCommercial AquacultureAlteration of the Freshwater Inflow PatternChanges in Water Quality

DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Perceived Threats

AgricultureCoastal FisheryMunicipal

CI-Mex’s Strategy for Addressing Threats

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Acknowledgements

Sources Cited

ANNEX A: The study area in Mexico.

ANNEX B: The Mocorito River basin and Santa Maria Bay.

Photographs (separate)

4

TRIP REPORT

Mocorito River BasinAndSanta Maria BaySinaloa, Mexico

May 2, 2002

MICHAEL J. IRLBECKU.S. Bureau of Reclamation300 East 8 th Street, Suite 169-GAustin, Texas 78701 U.S.Amirlbeck@gp.usbr.gov

INTRODUCTION

The author currently serves as an environmentalspecialist for the U.S. Bureau of Reclamation(Reclamation), and was on detail with U.S. Agency forInternational Development’s Water Team for the periodof February 18 through May 3, 2002. His primary dutieswith Reclamation include analyzing the environmentalimpacts from a variety of water resources developmentand management activities in the southern Great Plainsof the United States, with special experience in estuaryinflow issues.

Purpose and Scope of the Trip

The author participated in a field trip to Sinaloa, Mexico,during the period of April 18-26, 2002. The primarypurpose of this trip was to collaborate withConservation International-Mexico (CI-Mex) on theiractivities in Santa Maria Bay and the Mocorito Riverwatershed, Sinaloa, Mexico. The author was also giventhe opportunity to present some of Reclamation’sexperience in managing freshwater resources for bayand estuary needs at three State university campuses.

Information presented in this trip report was derivedprimarily from personal observations during a fieldreview of the watershed and from discussions, meetingsand direct inquiries with the various user groupsassociated with CI-Mex’s activities. These groupsincluded, but were not limited to, fishermen,aquaculturists, farmers, municipal officials, universityprofessors, students, state and federal agencyrepresentatives, conservation groups, and residents.

Report Objective

The purpose of this report is to provide a cursory,watershed perspective of the most significant water-related issues in the Mocorito River and Santa MariaBay.

Overview of Sinaloa

The State of Sinaloa, Mexico includes some 60,000 km2 ofland located in a narrow strip between the Gulf ofCalifornia and the La Sierra Madre mountain range. TheState runs generally northwest to southeast for some6,900 kilometers (km) and is crossed by 11 fertile rivervalleys. These rivers drain seasonally heavy rainfallfrom the uplands and mountains along the northeasternborder to a series of estuaries, bays and lagoons alongthe southwestern border of the State.

Topography in the State is quite variable, ranging fromapproximately near sea level to roughly 1,000 meters (m)in the foothills of the Sierra Madres. Moving north andeast from the Gulf, relatively flat coastal areas give wayto rolling country with arroyos, while canyons, cliffs andwaterfalls characterize the foothills of the sierras1.Similarly, the geomorphology of the State varies fromgentle slopes along the alluvial coastal plains (composedprimarily of unconsolidated sediments) to steepergradients of acidic rocks (of igneous origin and clasticsediments) near the mountains2.

The water resources of the State are commerciallyimportant, with easily 50%3 of the State’s residents beingsupported by the agriculture industry and as much as15% by its coastal fishery resources. Sinaloa has over800,000 hectares of irrigable land and 296,000 hectares ofestuary. The population of Sinaloa is about 2.5 million,with an estimated annual growth rate of about 4%.

There is an extremely pronounced wet/dry seasonalpattern to the local climate of Sinaloa. Rainfallpredominates the summer months (July throughOctober), during which daily rains are common. Asecond, somewhat less reliable rainy season occursduring December through January. The dry seasonbegins in earnest about April and extends through June.

1 Olson et al. 2001.2 FAO 1998, as cited in Olson et al. 2001.3 Unless otherwise indicated, the facts and figures presented

in this report were based on conversations withindividuals representing a variety of interests in thewatershed, and have not been verified from primarysources.

5

Sinaloa’s proximity to the coast minimizes fluctuationsin annual temperature. Summer months are hot andwinter months are mild.

OBSERVATIONS

The subject of the present report is one of the 11 Sinaloanrivers, the Mocorito River, and its association with SantaMaria Bay.

The Mocorito4 River Basin

Located in the north-central part of the State of Sinaloa(Annex A), the Mocorito River has historically been theprimary source of fresh water for Santa Maria Bay. Theriver itself is relatively small, stretching only about 100km from its headwaters to its mouth. The bay and itsnumerous islands are protected from the Gulf ofCalifornia by a long, linear barrier island.

For purposes of this report, the Mocorito River basin isdivided into three ‘zones’. Beginning with the highlandsand progressing to the coast, these zones include theupper basin , the coastal plains and the estuary5. In manyways, these generalized areas accurately describe mostof the northern river basins in Sinaloa. In fact, due to therelative flatness of the land in the lower watersheds,individual basins are not easily distinguishable, andthese three ‘zones’ may be considered somewhatcontiguous, narrow regions extending from northwest tosoutheast for much of the State.

THE UPPER BASIN

The upper basin of the Mocorito River generallyincludes the headwaters of the river in the mountainsdown to the city of Guamuchil (population of about100,000) (Annex B). In the upper elevations, nativevegetation in this zone is dominated by pine forestsadapted to xeric, acidic and nutrient-poor conditionsthat occur primarily in the dry season6. In the lowerelevations, scrub woodlands and forests are thedominant native vegetation types in the lowerelevations.

4 Mocorito means ‘land of the dead’.5 In this report, the term ‘estuary’ refers to the whole of

Santa Maria Bay, including the tidally influenced areasalong the coast.

6 Horwich and Lyon 1990, as cited in Olson et al. 2001. Inthis work, Horwich and Lyon principally described theBelizean pine forest ecoregion. However, they recognizedthat there are two other isolated patches of this ecoregiontype globally, one of which is located along much of thewestern Mexican coast. These locations are consideredpart of the same ecoregion due to similarities in climateand soil.

During the dry season, there is little or no flow in theMocorito River within the upper basin. During the wetseasons, frequent rains maintain continuous flows, andoccasional tropical storms cause the river to flood.

The human population is not very dense in the upperbasin.

THE COASTAL PLAINS

The coastal plains generally extend from the city ofGuamuchil down to the tidal influence of Santa MariaBay. This zone is comprised of a very fertile river valleylying within a region of broad, near-level plains. Nativevegetation is dominated by species common to the dryseasonal, forests of Sinaloa and Sonora; namely, from thefamilies Acaciaceae, Burseraceae and Leguminosae,although cacti are often conspicuous and abundant7.

Unlike in the upper basin, the Mocorito River in thecoastal plains has historically been capable of supportinga small amount of base flow during most of the dryseason. During the wet season, the river channel iseither full or flooding most of the time. Flood events aremore frequent and severe in the coastal plains than inthe uplands, especially during tropical storms.

Almost all of the basin’s irrigable land lies within thiszone, which also contains the highest human populationdensity.

THE ESTUARY

Finally, the estuary of the Mocorito watershed generallyincludes an array of inland flats, tidal marshes, coastaldunes, lagoons and barrier islands associated with SantaMaria Bay. Mangroves dominate native vegetationassemblages in the estuary. Found in coastal areas withsignificant riverine influences, mangroves are importantfor maintenance of high estuarine productivity8 becauseof their ability to synthesize organic matter, promotenutrient filtering and provide essential habitat for avariety of other species.

The salinity gradient in the estuary is seasonal,corresponding to freshwater inflow pulses from thebasin. During the wet period, the salinity of water in thebay can be almost fresh (>1 part per thousand salt (ppt)).As the wet season ends and runoff diminishes, saltwater from the Gulf of California (about 36 ppt)infiltrates the bay via currents and tides. Toward theend of the end of the dry season, when freshwaterinflow to the estuary from the river is nominal or non-

7 Olson et al. 2001.8 Gallegos 1986, as cited in Olson et al. 2001.

6

existent, bay salinity concentrations of >30 ppt are notuncommon.

Seasonally, there are two freshwater pulses duringwhich shrimp populations heavily utilize the estuary.The largest pulse occurs from July to October (utilizedby white and blue shrimp), and a second, smaller andless consistent pulse occurs during December andJanuary (utilized by brown shrimp). The estuarine zonealso supports large numbers of fish, crabs and bi-valves,as well as numerous bird and mammal species.

There are several smaller towns and villages locatedalong the mainland of the estuarine zone of thewatershed, including La Reforma (population of 6,600),Costa Azul (population of 1,400) and Playa Colorada(population of 870).

Human Alterations in the Mocorito River Basin

Human activity has affected, to some degree, most of thewatersheds in the world. The primary alterationsobserved in the Mocorito River basin during the courseof the field trip are presented by zone.

THE UPPER BASIN

Time did not permit a field survey of the upper reachesof the Mocorito River watershed. From what could begathered by conversation, the primary land uses in theupper basin include timber harvest (primarily pine andprecious hardwoods), ranching (cattle are bred in thehighlands and then raised in the fertile valleys to thewest) and some mining. To what extent, if any, theseactivities have affected the water resources of the upperMocorito River basin is uncertain. The authorunderstands that much of the Sierra Madre region isprotected as a natural area.

At the time of this survey (about one month into the dryseason), there was no base flow in the Mocorito Riverabove the city of Mocorito. When dry, much of the riverbottom serves as a source for gravel9 and clay, the laterof which is used locally to make bricks for buildingconstruction.

THE COASTAL PLAINS

Within the coastal plains of the watershed, there havebeen two primary human alterations affecting waterresources: the development of extensive agriculturepractice and the growth of municipalities.

9 Although no surface flow was observed, the groundwater

table in the river valley was generally no deeper than 1 to2 m, and was exposed in pits associated with gravelquarry activities.

Agriculture Practice

The most significant human impact to the waterresources of the coastal plains of the Mocorito Riverbasin is the advent of irrigated agriculture. Beginning inthe 1930’s, agriculture practice began to increase,primarily along the river floodplain, being irrigated withshallow wells in the river alluvium or from local riverdiversions. However, in 1972, the General EustaquioBuelna Dam10 (Buelna Dam) was constructed on theMocorito River, just upstream of the city of Guamuchil,about 45 km from the river’s mouth. As part of a large-scale water delivery system11, this and other similarfacilities in the northern part of the State enabledirrigated cultivation of almost the entire coastal plain.

Based on discussions with a representative of Mexico’sNational Water Commission (CNA), the dam isgenerally operated to capture all of the first rains of thewet season, and does not release water downstreamuntil the reservoir is sufficiently full to assure water forirrigation. Peak irrigation season is in October, duringwhich time the dam delivers about 20 to 25 cubic metersper second (m3/s) into the irrigation canal12. Deliveries

10 Named after a Sinaloan hero in Mexico’s 1910

revolutionary war, this is the only dam in the MocoritoRiver basin. A plaque at the dam states that the reservoirhas a maximum storage capacity of 343.8 M m3, of which115.8 M m3 is reserved for agriculture, 96.7 M m3 for floodcontrol, 96.3 M m3 for ‘super-storage’ (or, surcharge pool)and 35.0 M m3 for sedimentation. However, it wasreported that, due to the lack of gage data in the upperbasin, and therefore the ability to anticipate the timing andmagnitude of flood events, the reservoir level must be keptlower than its design capacity. As a result, only about 80M m3 were said to be available for irrigated agriculture,which is only about 70% of the original capacity dedicatedfor this use.

11 This facility was part of a State-wide irrigation systemdevelopment project that combined the water resources ofseveral of the State’s (northern) rivers to support what iseffectively one extensive agriculture region in the coastalplains. For example, irrigation water diverted from a damon the Culiacan River (located immediately south of theMocorito) is joined with irrigation water from theMocorito River just downstream of the city of Mocorito, sothat the intervening farmland is jointly served by multi-basin water. Of the 11 rivers in Sinaloa, 7 have at least onelarge reservoir and 2 rivers have two. The 4 southern mostrivers do not have dams.

12 CNA stated that the main irrigation canal from the damhas a maximum capacity of approximately 40 m3/s. Themain canal from Buelna Dam is joined by another largecanal from a dam on the Culiacan River. This combinedirrigation system then serves much of the irrigated land inthe region. It was unclear whether the stated maximumcapacity referred to that of the main canal out of BuelnaDam, or that of the combined main canal.

7

continue into the dry season (about 4 m3/s was beingdelivered during the field review (late-April)). Due tothis operational scheme, there is a great fluctuation inthe annual water level of the reservoir. Even so, apopular freshwater fishery in the lake has developedsince the dam’s construction.

Due to the favorable climate, irrigation enables theharvest of two or three crops per year. Primary cropsinclude corn, tomatoes and other vegetables, grains,cotton, hay, and others. As part of the agricultureindustry, the advertising and use of agriculturechemicals (e.g., herbicides, pesticides and fertilizers) iswidespread.

The irrigation system in the coastal plains exhibitsconsiderable opportunities for efficiencyimprovements13. Several of the main canals are linedwith concrete, while most of the laterals are earthen. Atseveral locations, irrigation water in the canals issupplemented by adjacent groundwater wells, whichcapture alluvium and (presumably) seeped water andplace it back into the canal. Irrigation water flowing offof individual farms is eventually collected into largedrainage canals14, which then discharge return flowsinto Santa Maria Bay at several locations. The flowvolume of any one of these major drainage ditches intothe estuarine zone is substantial, even during the dryseason.

The river bottom itself and adjacent floodplain in thecoastal plains are extensively farmed during the dryseason. As there are no releases from the dam into theriver below Guamuchil, what water that is in the riverduring the dry season is derived from a combination ofmunicipal effluent and some irrigation return flows (seethe next section, Municipal Use). This flow is eitherpumped out of the floodplain or distributed directlywithin the river channel for irrigation. As a result, thereis very little, if any, discharge from the river into SantaMaria Bay during the dry season.

Municipal Use

The city of Guamuchil draws its municipal water fromthe river itself, having constructed a small, earthen dikea few kilometers downstream of Buelna Dam toimpound water. The dike creates a small, artificial lake

13 One estimate is that the total water efficiency of the

irrigation system is only about 50%.14 In all, there are 6 major irrigation drains that flow into

Santa Maria Bay. These drains receive return flows fromagriculture land irrigated by water from both the Mocoritoand Culiacan Rivers.

within the city that is re-supplied from the reservoir bysmall releases made two or three times a week duringthe dry season15. During this time, there is no river flowdownstream of this dike, although there exists somelocal memory of a small base flow in this reach of theMocorito River before the dam was constructed16. Eachyear when the rainy season begins, the dike is removedto prevent flooding of the community, and municipalwater is withdrawn directly from the flowing river.

Most of the other communities in the coastal plain of thebasin that are near the river (e.g., Angustora, populationof 4,400) draw water from shallow wells. Based on theinformation available, the typical treatment process forthese communities is comprised of simple filtration andchlorination.

None of the municipalities in the basin have awastewater treatment facility17. Raw sewage (knownlocally as aguas negras , or ‘black waters’) is dischargeddirectly into the river downstream of each community18.In the case of the city of Guamuchil, an additional sourceof excrement is released into the river (at an estimatedrate of about 100 liters per second) from a livestock

15 As previously discussed, there is no storage capacity in

Buelna Dam dedicated for municipal use. The fact thatwater from the reservoir is regularly released during thedry season for the city of Mocorito may contributesomewhat to the reduced amount available for agriculture(see Footnote 10).

16 The observation that the Mocorito River once supported asmall base flow during the dry season may be possiblyexplained by the combination of two factors. First, beforethe dam, the uncontrolled flows and floods of the riverlikely charged the bank storage (i.e. alluvium) of the riverfloodplain during the wet season. This water then slowlydischarged into the river channel once the rainsdiminished. With the capture and storage of a largeamount of the flood flows, bank storage may not be asgreat. Second, the operation of numerous municipal andagricultural wells in the shallow alluvium of thefloodplain continually dewaters bank storage, and so limitnatural discharge into the river.

17 The city of Mocorito has constructed a sewer lift stationand pipeline to some oxidizing lagoons intended forsewage disposal. The lagoons were then to be used as asource for irrigation by adjacent farmers. However, about2 km of the pipeline has deteriorated (due to a suspecteddesign deficiency), and the facility is not operational. It isestimated that about $2 M pesos is required to repair thepipeline.

18 This circumstance is common for most of Sinaloa. Eventhe city of Culiacan (population of approximately1,000,000, and the largest city in Sinaloa) treats only about40% of its effluent to an advanced primary level. Thisvolume, along with the remainder of the untreatedeffluent, is discharged directly into the Culiacan Riverdownstream of the city.

8

slaughterhouse facility located only a few kilometersdownstream.

Although not a direct impact to water resources, theaccumulation of municipal garbage in the river bottomand general floodplain should also be briefly discussed.As there is no regional or local garbage collection anddisposal service for many, if not all, of the communitiesin the watershed, discarded refuse, paper, plastic andglass accumulate from personal disposal alongroadways, irrigation drainage ditches and streamchannels that surround each community. During thewet season, much of this material is washeddownstream and into the bay.

With the contribution of municipal effluent (and someirrigation return flow), dry season base flow in theMocorito River in the coastal plains gradually increasesdownstream. However, most of this flow is reused forirrigation before it reaches the bay (see previous section,Agriculture Practice). Undoubtedly, effluent is alsodischarged during the wet season when the river isflowing full, but such contributions are not as readilydiscernable because of dilution.

The degree of contamination, if any, of surface andground water resources in the coastal plains by eitheragricultural chemicals or nutrients is not known. Giventhe extent of agriculture practice in the region and thecommon release of sewage into the river, suchcontamination is certainly possible.

THE ESTUARY

Human alterations of the estuary have resulted fromactivities within the estuarine zone itself (e.g., theintensification of the shrimp industry and an increase incommercial aquaculture) and from activities within thewatershed upstream (e.g., potential changes in thefreshwater inflow pattern, water quality and the naturalsedimentation rate).

Intensification of the Shrimp Industry

The residents of the Sinaloan coast have long relied onthe productive shrimp populations. However, theharvest pressure on this resource has dramaticallyincreased over the past several decades. In 1950, therewere approximately 500 shrimp fishermen in SantaMaria Bay. In 2000, there were an estimated 10,000.There has not been, however, a significant change in thetotal volume of shrimp caught over this same period.On average, about 1,500 tons of shrimp are still caught

each year, with bad-year catches being as low as 600tons and good-year19 catches as much as 5,000 tons.

What has changed is the duration of the shrimp harvest.In 1950, 500 fishermen would spend a total of about 4 to5 months harvesting shrimp. In 2000, 10,000 fishermenspend only about 4 weeks20, or perhaps 6 weeks duringan El Niño year.

There is local memory of there generally being moreshrimp in the bay. This perception may be indicative ofthis intensification of harvest pressure, or the influenceof other factors (e.g., a change in the freshwater inflowpattern or deterioration in water quality, both of whichare discussed in the next section), or a combination ofthese.

Commercial Aquaculture

Commercial aquaculture (primarily shrimp farms) havebecome abundant along the Sinaloan coast. Thesefacilities are developed by either private or corporateventures. Typically, these facilities include theconversion of tidal flats or marginal cropland into aseries of constructed ponds. The industry is morecommon in the southern part of the State, but isbeginning to growing in the Santa Maria Bay area.

Operationally, these facilities use a combination of freshwater (diverted primarily from agriculture drainageditches) and bay water, although there are some facilitiesthat are purely marine-water systems. Young shrimpare stocked into the ponds, fed and then harvested.Excess water from these facilities is discharged into thecoastal waters of the State. When functioning asdesigned, two or three harvests of shrimp per year canbe made from these aquaculture ponds. As with anyartificial concentration of animal populations,environmental parameters like water quality, foodavailability and disease must be intensively managed.

Alteration of the Freshwater Inflow Pattern

Several of the aforementioned human activities in thewatershed are suspected by the author of having alteredthe natural pattern and distribution of freshwater inflow

19 There is a reported direct correlation with the abundance

of shrimp during the harvest and the timing and durationof the wet season. For example, an early beginning to therainy season or an unusually wet one (like during an ElNiño year) will typically indicate a good harvest.

20 During these 4 weeks of harvest, two weeks are good, ofwhich 2 or 3 days are very good. The result is that about50% of a fisherman’s annual shrimp-generated revenue iscaught within only a few days of the harvest season. Theshrimp harvest comprises about 80% of a shrimpfisherman’s total annual income.

9

from the Mocorito River into Santa Maria Bay. Thesealterations include changes to the river’s natural flowregime and its distribution into the bay.

Changes in the river’s natural inflow regime: Suspectedchanges in the inflow pattern of the Mocorito Riverinclude changes in the magnitude, timing andduration of the annual freshwater inflow signal tothe bay.

First of all, there has almost certainly been areduction in the magnitude of the total amount offreshwater reaching Santa Maria Bay during the wetseason(s). This (relatively safe) assumption is basedupon the fact that most of the water stored in thereservoir does not directly reach the bay via theriver, but is captured, stored and diverted forirrigation by the dam. Also, with high temperaturesduring the spring and summer months, the amountof water that evaporates from the reservoir (and isthereby lost to the watershed) could also besubstantial21. Therefore, through a combination ofthese two factors, event magnitude has likely beenreduced by an (as yet) undetermined amount.

Second, there is a strongly suspected delay in thetiming of the seasonal inflow signals into SantaMaria Bay from the Mocorito River. As discussedpreviously, the current operations of Buelna Damare such that all of the first part of the wet seasonrunoff is captured in storage. When the reservoir issufficiently full to meet the needs of irrigation,additional inflow is passed downstream. Thisoperational scheme probably delays both the initialonset and ultimate peak of the wet season inflowpattern into Santa Maria Bay. The author suspectsthat these timing delays are manifested in the rangeof a few days to a few weeks22.

Finally, given an assumed reduction in the amountof water in the basin and a delay in the timing of itsarrival into Santa Maria Bay, there is also a strongpossibility that the overall duration of the seasonalinflow pattern of the Mocorito River has also beenreduced.

21 Evaporation loss is often a neglected, although significant,

‘cost’ (in wet water) of reservoir operations. For example,the annual evaporation from two south Texas reservoirscan be as high as 18 per cent of their combined totalstorage capacity.

22 This estimate is based upon the approximate amount oftime that it would take the reservoir to ‘fill up’ once thewet season rains have begun. It was reported that the damhas filled to operational capacity in as little as four daysduring remarkably heavy rains in the upper basin, but thiswas understood by the author to be an exceptionalcircumstance.

In summary, physical alterations to the MocoritoRiver have almost certainly affected the river’snatural flow regime23. However, without somebasic hydrologic analysis of the available streamflow gage data for the basin24, these suspectedchanges cannot be verified, much less quantified.However, for purposes of illustration, a conceptualrepresentation of these possible changes has beenconstructed (Fig. 1).

Fig. 1: Theoretical representation of the possiblechanges in the natural flow regime of the MocoritoRiver at its mouth in Santa Maria Bay. Obviouselements of the historic regime include two seasonalpeaks in river flow during the wet seasons (July-Octoberand December-January) and a period of low flow duringthe dry season (April-June). The present flow regimerepresents suspected changes due to human activities inthe watershed, including (a) a reduction in the magnitudeof the seasonal inflow signal, (b) a temporal delay in theseasonal peak of the inflow signal, (c) a temporal delayin the initiation of the inflow signal, and (d) a reduction inthe overall duration of the wet season inflow signal. Aconjectural decrease in the amount of natural base flowduring the dry season (see Footnote 16) is alsorepresented (e).

Changes in the distribution of flow to the bay:Historically, the most significant freshwater inflowto the bay was from the Mocorito River during wetseason. During the dry season, to the extent that the

23 For a general presentation and discussion of how the

ecological integrity of river ecosystems depends on theirnatural dynamic character, including functionaldefinitions of flow magnitude, timing, duration, etc., seePoff et al. 1997.

24 A CNA representative has stated there are only twooperating stream flow gages in the Mocorito River basin:one on the river just above the lake (to measure inflow),and one on the river immediately downstream of the lake(to measure outflow).

10

lower river did support a base flow, a small amountof fresh water would have also entered the bay.

However, with the hydrologic alterations caused bythe human activities, large amounts of water fromthe wet season are now stored in the reservoir andreleased slowly over time through the irrigationcanal network. Eventually, a portion of this andother waters25 make their way from the canals ontoindividual farms, and then off of the fields and intodrainage ditches. The drainage ditches convergeinto major drains and discharge directly into SantaMaria Bay.

It is unknown whether the total volume entering thebay from irrigation return flows during the dryseason is more or less than what historically enteredvia the river. The author suspects that the presentreturn flow volume is substantially greater26. If thisassumption is valid, then there has likely been ameaningful increase in the total amount offreshwater inflow to the bay during the dry season,as well as a change in its source location(s). Insteadof experiencing minimal freshwater inflow duringthe dry season from one source (i.e., the MocoritoRiver), the estuarine zone of the Santa Maria Bayexperiences artificially elevated freshwater inflowsduring the dry season (due to runoff from irrigatedagriculture) from several sources27.

The effect of this change to the estuarine zone ofSanta Maria Bay, if any, is not known. There issome evidence, however, that the upper reaches ofthe estuary associated with the main irrigationdrainage ditches are experiencing much fresherconditions. By boat, the outlet of one of these majorditches28 was investigated during the field trip. It

25 As previously discussed, these waters can include

supplemental groundwater and discharged municipaleffluent.

26 This conclusion is based on the fact that, during the dryseason, irrigation deliveries from Buelna Dam arerelatively low, but are usually at least about 4 m3/s. It isunlikely, in the author’s opinion, that the Mocorito Riverwas capable of this amount of natural flow during the dryseason.

27 It may be important to also note that even during the wetseason, the source locations for freshwater inflow to SantaMaria Bay have been similarly changed. During the peakof the irrigation season (about mid-October), 20 to 25 m3/sis released into the irrigation canal from Buelna Damalone. Combined with other canal flows diverted from theCuliacan River, the total freshwater signal into the estuaryfrom the drainage ditches during the wet season could besignificant.

28 The drainage ditch in question was located at the southernend of Santa Maria Bay, and drains fields irrigated withwater diverted out of the Culiacan River.

was observed that along the narrow channels of theupper estuary, either the mangroves were beingdisplaced by vigorous growths of cattail (Typhaspp.) and bulrush (Scirpus spp.), or these freshwaterspecies were out-competing mangroves in thecolonization of newly created mudflats. Althoughthe invasion of freshwater emergent vegetation wasthought to be possibly associated with a largetropical storm event in 199729, it is also possible thatthe artificially elevated and sustained volumes offreshwater provided to the upper estuary by thedrainage ditches is actively supporting suchinvasions.

Changes in the natural sedimentation rate:Sedimentation is a natural function of riverhydraulics. Lacking sufficient data for MocoritoRiver basin sediment processes, the author can onlyoffer two hypothetical changes. First, it would seemintuitive that below Buelna Dam, the sedimentationrate has been significantly reduced due to thecapture effect of the structure itself. In fact,approximately 10% of the total storage capacity ofthe reservoir (35 M m3) has been reserved for theinflux of sediment. Conversely, it would seemequally intuitive that the vast amount of land undercultivation in the State’s coastal plains wouldconsequently increase the amount of soil lost towater erosion, thereby increasing the sedimentationrate to the bay. These suspected changes arespeculative in nature, but are not inconsistent withgeneral hydrologic principles. At present, thequantitative or relative change in the actualsedimentation rate of the river or basin is unknown.

Changes in Water Quality

There is local concern about the possible changes thathave occurred to the quality of water resources in theMocorito River basin, especially within the estuarinezone. Although there is reported some scattered dataavailable on the subject, there is not a comprehensive

29 It is conceivable that a large flood event in the Sinaloa

region could result in large amounts of sediment beingimported into the upper estuary areas via the drainageditches, temporarily creating barren mudflats adjacent toexisting mangroves. If the event were to occur during theright time of year and were to suppress bay salinityconcentrations long enough, germination and subsequentgrowth of freshwater emergent vegetation could occur.However, given the annual occurrence of near-oceansalinity concentrations in these areas during the dryseason, the author believes it unlikely that such vegetationcould survive and actively reproduce without support ofsome persistent freshwater influence.

11

sampling and analysis program currently in effect30.Furthermore, what data that has been collected was notreadily available for review during the site visit.Therefore, as with the speculative changes previouslydiscussed regarding potential changes to the naturalflow regime and sedimentation rates, the author issimilarly reduced to discussing only the possible waterquality changes that have occurred in the estuarine zone.

Given the extent and type of human activity in thewatershed, a myriad of potential water quality issuescould be expected. From the author’s perspective, thereare two primary areas of potential alteration: namely,the increase in nutrients and the addition ofmanufactured toxins.

Increased nutrients:Increased nutrient loading to the Mocorito Riverwas evident from observed direct discharge ofuntreated municipal effluent and livestockexcrement into the river near Guamuchil. As mostof the river water in the lower portions of thewatershed is locally diverted for agriculture, mostof this nutrient material ends up on an agriculturefield. Irrigation return flows from these fields couldcontain remnant municipal nutrients as well as anynumber of fertilizer products applied by the grower.In many cases, it was observed that some of theirrigation return flow was returned to the river, onlyto be re-diverted again onto a field furtherdownstream. Ultimately, all irrigation return flowsare discharged into Santa Maria Bay.

If there happens to be an aquaculture facility usingthis discharge water, then certain processes at thisfacility could also contribute nutrient materials.This aquaculture water is also eventuallydischarged into the bay.

Given these instances, the opportunity for multiplenutrient additions to the water resources of theMocorito River basin is quite possible.

Introduction of manufactured toxins:The primary potential source for the introduction ofchemical toxins into the water resources of theMocorito River is the application (and subsequent

30 In addition to the general lack of resources and capacity

for extensive water quality monitoring, there has beensome level of (at least perceived) resistance to suchinvestigations in the watershed. It is generally recognizedthat the local economic sectors representing individualand corporate growers, as well as agriculture chemicalmanufactures and distributors, are most sensitive to suchanalyses. Given the economic and political status of theagriculture industry as a whole in Sinaloa, this resistancewould be anticipated.

runoff) of a variety of agriculture chemicals,specifically herbicides and pesticides.Comprehensive information about the use of thesechemicals (e.g., types of chemicals used, applicationrates, application methods, etc.) is almost non-existent for the State of Sinaloa. Furthermore,although some extensive national regulations31 doexist regarding the use of agriculture chemicals,their enforcement is often inconsistent.

Other possible sources of toxic chemicals couldinclude any mining activity in the upper basin orfrom municipal garbage. The potential contributionof these sources, however, is probably relativelyinsignificant compared to that of agriculturechemicals.

DISCUSSION

Having summarized the general character of theMocorito River basin and discussed its primaryalterations by human activity, some effort can now bemade to identify the primary human values placed on itswater resources. From the author’s perspective, thesevalues principally include its agricultural, coastal fisheryand municipal uses.

The following discussion, then, is based on the author’s(admittedly limited) perception of the most criticalthreats to these identified values. This section is thenconcluded with a summary of the strategy and status ofCI-Mex’s activities in the region.

Perceived Threats

For each principle value, the primary perceived threatsare identified and discussed.

AGRICULTURE

• Compromised production of agricultural land. Thisthreat may be considered, to some degree, to be self-perpetuating. If, as suspected, the continued use ofagriculture chemicals impairs the natural microbialprocesses in the soil that contribute to productiveplant growth, then it is likely that more chemicalswill be added to compensate for the reduction.This, in turn, may lead to further deteriorations inthe soil’s natural ability to sustain productive plantlife. In addition to being expensive, a significantdependence on fertilizers, herbicides and pesticidesmay limit overall crop production. However, verylittle information is presently available on the

31 These regulations have been primarily developed and

implemented to comply with various provisions of certaininternational trade agreements.

12

subject in the watershed, and the significance of thisthreat to the agricultural value of water forirrigation is unknown.

COASTAL FISHERY

• Unregulated harvest pressure on shrimp resources .Although numerous regulatory restrictions apply tothe commercial shrimp industry in Sinaloa,sufficient legal enforcement is generally lacking.For example, it is presently illegal to fish for shrimpin the Gulf of California outside of Santa Maria Bay,but this restriction is rarely enforced32. Ultimately,harvest pressure must be effectively managed for ahighly productive shrimp fishery to be reliablysustained.

• Current operation of Buelna Dam and reservoir . Thesignificant degree of impact that reservoiroperations can have on the natural flow patterns ofrivers is well documented33. The current operationof Buelna Dam for irrigated agriculture potentiallythreatens the productivity of the coastal fishery ofSanta Maria Bay in two principal ways. First,reservoir operation continues to impair the seasonalfreshwater signal into the bay (i.e., the magnitude,timing and duration of inflow events). Second,reservoir operation may also be contributing to theloss of mangrove habitat from emergent marshencroachment in the upper areas of the estuary.However, to the author’s knowledge, neither ofthese issues has been adequately studied to allow areasonable estimate of the magnitude or scope oftheir potential threat to the coastal fishery34.

• Future diversions from the Mocorito River. One of themost serious threats, but possibly one lessimmediate, is that of additional future developmentof the water supplies of the Mocorito River. Such

32 It is estimated that as much as 50% of the total annual

shrimp harvest of Santa Maria Bay is actually caught in theGulf, and is therefore illegal.

33 Poff et al. 1997.34 It is not anticipated that such a hydrologic analysis (which

could be as simple as a rudimentary water budget for thebasin) would be excessively difficult to develop. Itsbenefits could potentially be many. First, it would allowthe characterization and presentation of different aspectsof the natural flow regime (e.g., flow magnitude, timingand duration) over a temporal scale (e.g., daily ormonthly), similar to Fig. 1. Next, such an analysis couldalso be used to characterize the hydrographic changes inthe Mocorito River basin over time, greatly assisting theassessment of historical impacts to the estuarine resourcesin Santa Maria Bay that have adapted to the historicpatterns of freshwater inflow. Finally, this assessmentcould provide a foundation for insight and analysis ofother issues (e.g., water quality changes) in the watershed.

development could be instigated in response to theneeds of agriculture or growing municipalities, orboth. For example, as previously discussed, thepresent operation of Buelna Dam does not supplythe full amount allocated to agriculture (seeFootnote 10). This implies an existing, unmetdemand for additional irrigation water.

Furthermore, the representative for the federalMexican agency responsible for water developmentand management (CNA) stated that plans for asecond dam in the Mocorito River basin upstreamof Buelna Dam have been completed but thatfunding had not yet allocated for the project35. Thisstructure would provide an estimated additional200 M m3 annually for irrigated agriculture in theregion. If constructed, this facility could beexpected to further exaggerate the alterations to thenatural flow regime of the Mocorito River into thebay, as well as amplify to the water quality issuesby enabling a substantial increase in total irrigatedarea in the region.

• Contamination of freshwater inflow to the estuary.Because of the potential (by design) for nutrientsand biocides to affect critical biological processes,the concern that sewage, fertilizers, herbicides andpesticides may affect the coastal fishery islegitimate. Although specific data for pollution ofthe Mocorito River or Santa Maria Bay was notreadily available, it is generally known that watercontamination can and do impact aquaticecosystems. For example, pesticides are known toproduce endocrine and reproductive damage inorganisms, and high levels of nutrients can causeeutrophication in the lakes and rivers and continueon into coastal areas36. But again, the magnitude,scope and extent of the threat of contamination inthe estuary are difficult to determine withoutextensive review and analyses of existing data.

• Altered sedimentation rate into the bay. Thecontribution of river sediments to a bay is a naturalprocess. In the case of the Mocorito River, thisnatural process has been altered by reservoirconstruction and regional land use practices.Significant decreases in sedimentation could lead tothe reduction in the impact of natural nutrientmaterials and the submergence of shallow waterhabitats. Significant increases in sedimentation

35 The exact status of funding for this facility was not

precisely clear. There was the general indication that iffunding were to be made available, it might be severalyears from now.

36 Source: EduGreen, an educational initiative for schools bythe Tata Energy Research Institute(http://edugreen.teri.res.in/index.htm).

13

could lead to turbidity problems and loss of shallowwater habitats. Theoretically, either of these twoconditions could threaten estuary productivity, butit is unclear which, if either, actually threatens thecoastal fishery.

MUNICIPAL

• Public health risk from lack of water sanitation.There are two main public health risks commonlyassociated with water quality degradation due toraw sewage contamination: fecal-oral (diarrhoeal)disease transmission and nitrate poisoning37. In theMocorito River basin, the discharge of rawmunicipal sewage and livestock excretions into theriver contaminates both the surface and groundwater resources of the watershed. Downstreamcommunities then withdraw shallow groundwateror surface water from the river for municipal use.These circumstances pose a clear potential humanhealth risk through two different possible exposurevectors; namely, direct contact and ingestion.

• Public health risk from chemical contamination of sourcewater. Chemicals introduced into drinking watersources can cause serious health effects in humans.In the Mocorito River basin, the primary potentialsources of surface and ground water contaminationare from agriculture runoff and raw sewage.Chemical ingredients present in pesticides can affectand damage the human nervous, reproductive andendocrinal systems, and can cause cancer38.Elevated levels of nitrates from either fertilizer orsewage can prove fatal to humans, especially toinfants39. The actual public health threat fromchemical contamination of municipal source waterin the Mocorito River basin is commensurate withthe degree to which actual contamination hasoccurred, and if so, to the degree which these watersupplies are treated and consumed. Unfortunately,these relationships are not presently well known.

CI-Mex’s Strategy for Addressing Threats

Given the short amount of time spent in the region and avery limited development assistance background, theauthor is reluctant to even attempt a discussion of CI-Mex’s activities in Sinaloa. Nevertheless, during thecourse of the time spent in Mexico, the author wasexposed to and participated in a variety of CI-Mex’sactivities in the Mocorito River basin and Santa Maria

37 Cave and Kolsky 1999.38 Source: EduGreen, an educational initiative for schools by

the Tata Energy Research Institute(http://edugreen.teri.res.in/index.htm).

39 Ibid.

Bay. From this limited perspective, key elements of CI-Mex’s strategy for addressing the potential threats to thewater resources of the basin were apparent.

The primary focus of CI-Mex’s activities in Sinaloa is thelocal communities; or, those groups of people who eitherdirectly utilize water or who must bear some of theconsequence for water management decisions. Fromthese communities, CI-Mex has organized and facilitatesa number of diverse working groups in severallocations, whose individual members include fishermen,residents, students, teachers, governmental officials,business representatives and others. Because of thisdiversity, the participants in these groups address thewater resource issues of the basin from different pointsof view, but in an open, participatory process thatencourages cross-pollination if ideas and mutualeducation.

The primary message presented to these groups by CI-Mex is that they have the ability to affect improvementsin their watershed, and therefore in their lives. Thisemphasis on enabling local communities to take theinitiative in identifying problems and coming up withsolutions has significant strategic value. Primarily, itreduces dependency on government structure40 forimmediate intervention and mobilizes a far greatercritical mass of human effort.

In the author’s (previously qualified) opinion, CI-Mex’scommunity-based approach, which is largelyindependent of direct government support, appears toshow promise for long-term results because it is broadlysupported by substantial local interest and energy.

40 There appears to be some inherent difficulties in

establishing and maintaining strong, long-term politicalsupport and funding for local programs within theMexican governmental system. The regional/municipalgovernments are elected every three years, with noopportunity for the incumbents to be immediately re-elected. Similarly, the national governmentrepresentatives have a limited term of 6 years, with noopportunity for immediate re-election. This results in amajor shift in political leadership every few years, andoften an adjustment in the expressed support forindividual programs or activities. Therefore, sustainingdirect funding and political support for local, long-terminitiatives is recognizably difficult. Additionally, thegeneral failing of consistent enforcement of a variety ofwater-related regulations limits governmentaleffectiveness.

14

CONCLUSIONS

The objective of this report was to provide acursory, watershed perspective of the mostsignificant water-related issues in the MocoritoRiver basin. In summary, the author is left withthe following conclusions:

• The inland and coastal water resources ofSinaloa are important to both the economy ofthe State and to the livelihood of its residents.

• The primary human values placed upon thesewater resources are primarily associated withtheir agriculture, coastal fishery and municipaluses.

• There are several ongoing human activities inthe watershed that threaten, to some degree,the value of each of these uses.

Threats to agriculture use include thecompromised production of agricultural land.

Threats to coastal fishery use includeunregulated harvest pressure on shrimpresources, current operation of Buelna Damand reservoir, future diversions from theMocorito River, contamination of freshwaterinflow to the estuary, and an alteredsedimentation rate into the bay.

Threats to municipal use include public healthrisks from lack of water sanitation andchemical contamination of source water.

• The magnitude and extent of these threats arevery much limited by the lack of sufficientdata and analyses.

• CI-Mex’s community-based approach appearsto be reasonable and effective in betterunderstanding the present threats and indeveloping and implementing potentiallyviable solutions.

Acknowledgements

The author would like to acknowledge thefollowing:

The University of Sinaloa: for their kind receptionsin Guamuchil, Culiacan and Mazatlan.

Ariel and Beto : for a great tour of the bay and avery good lunch.

Freddie, Sammy, Joel and George: for world-classulama lessons.

Armando and Anna: for great food, company,Spanish lessons and overall interpretiveservices.

Sources Cited

CAVE, BEN and PETE KOLSKY. 1999. Groundwater,latrines and health. WELLstudy Task No. 163.London School of Hygiene and Tropical Medicine,WEDC, Loughborough University, UK.

FAO. 1998. Soil and terrain database for Latin Americaand the Caribbean, 1:5 million scale, FAO, Land andWater Digital Media Series N°5. Food andAgriculture Organization, Rome, Italy.

GALLEGOS, M. 1986. Petróleo y manglar. Serie MedioAmbiente en Coatzacoalcos Vol. III. Centro deEcodesarrollo, México.

GENTRY, A.H. 1995. Diversity and composition ofneotropical dry forests. Seasonally dry tropicalforests. S.H. Bullock, H.A. Mooney, and E. Medina,editors. Cambridge University Press, Cambridge.

HORWICH, R.H., and J. LYON. 1990. A Belizean rainforest: the community baboon sanctuary. Orang-utan Press. Gays Mills, Wisconsin.

OLSON, DAVID M., ERIC DINERSTEIN, ERIC D.WIKRAMANAYAKE, NEIL D. BURGESS, GEORGE V.N.POWELL, EMMA C. UNDERWOOD, JENNIFER A.D’AMICO, ILLANGA ITOUA, HOLLY E. STRAND , JOHN C.MORRISON, COLBY J. LOUCKS, THOMAS F. ALLNUTT,TAYLOR H. R ICKETTS, YUMIKO KURA, JOHN F.LAMOREUX, WESLEY W. WETTENGEL, PRASHANTHEDAO, and KENNETH R. KASSEM. 2001. Terrestrialecoregions of the world: a new map of life on earth.BioScience, Vol. 51, No. 11.

POFF, N. LEROY, J. DAVID ALLAN, MARK B. BAIN, JAMES R.KARR, KAREN L. PRESTEGAARD, BRIAN D. RICHTER,RICHARD E. SPARKS, and JULIE C. STROMBERG. 1997.The natural flow regime: a paradigm for riverconservation and restoration. BioScience, Vol. 47,No. 11, pp. 769-784.

15

ANNEX A: The study area in Mexico. Source: http://www.maps-of-mexico.com.

16

ANNEX B: The Mocorito River basin and Santa Maria Bay. Approximate scale is 1:500,000. Source:http://www.maps-of-mexico.com.