Hydrology
Relative scales of time and effectiveness of watershed processes in a tropical montane rain forest of puerto rico
Mon, 07/25/2011 - 11:49 — ckassScatena FN. 1995. Relative scales of time and effectiveness of watershed
processes in a tropical montane rain forest of Puerto Rico. Pages 103–111
in Costa JE, Miller AJ, Potter KW, Wilcock PR, eds. Natural and Anthropogenic
Influences in Fluvial Geomorphology.Washington (DC):
American Geophysical Union. Geophysical Monograph 89.
Streams of the Montane Humid Tropics
Mon, 07/25/2011 - 11:37 — ckassAbstract:
Tropical montane streams produce a disproportionately large amount of the sediment and carbon that reaches coastal
regions and have often been considered to be distinct fluvial systems. They typically drain orogenic terrains that have not
been recently glaciated, but have undergone climatic changes throughout the Pleistocene and currently receive
2000–3000 mm or more of precipitation each year. Steep gradient reaches with numerous boulders, rapids, and waterfalls
that alternate with lower gradient reaches flowing over weathered rock or a thin veneer of coarse alluvium characterize these
streams. Although their morphology and hydrology have distinctive characteristics, they do not appear to have diagnostic
landforms that can be solely attributed to their low-latitude locations. While they are relatively understudied, an emerging
view is that their distinctiveness results from a combination of high rates of chemical and physical weathering and a high
frequency of significant geomorphic events rather than the absolute magnitudes of individual floods or other geomorphic
processes. Their bedrock reaches and abundance of large and relatively immobile boulders combined with their ability to
transport finer-grained sediment also suggest that the restorative processes in these systems may be less responsive than in
other fluvial systems.
MULTIVARIATE ANALYSIS OF WATER QUALITY AND PHYSICAL CHARACTERISTICS OF SELECTED WATERSHEDS IN PUERTO RICO
Mon, 07/25/2011 - 11:33 — ckassSANTOS-ROMA´ N, D., G. S. WARNER, AND F. SCATENA. 2003.
Multivariate analysis of water quality and physical
characteristics of selected watersheds in Puerto Rico.
Journal of the American Water Resources Association 39:
829–839.
Abstract:
Multivariate analyses were used to develop equations
that could predict certain water quality (WQ) conditions for unmonitored
watersheds in Puerto Rico based on their physical characteristics.
Long term WQ data were used to represent the WQ of 15
watersheds in Puerto Rico. A factor analysis (FA) was performed to
reduce the number of chemical constituents. Cluster analysis (CA)
was used to group watersheds with similar WQ characteristics.
Finally, a discriminant analysis (DA) was performed to relate the
WQ clusters to different physical parameters and generate predicting
equations. The FA identified six factors (77 percent of variation
explained): nutrients, dissolved ions, sodium and chloride, silicacious
geology, redox conditions, and discharge. From the FA, specific
conductance, sodium, phosphorous, silica, and dissolved oxygen
were selected to represent the WQ characteristics in the CA. The
CA determined five groups of watersheds (forested, urban polluted,
mixed urban/rural, forested plutonic, and limestone) with similar
WQ properties. From the five WQ clusters, two categories can be
observed: forested and urban watersheds. The DA found that
changes in forest cover, percent of limestone, mean annual rainfall,
and watershed shape factor were the most important physical features
affecting the WQ of watersheds in Puerto Rico.
A SURVEY OF METHODS FOR SETTING MINIMUM INSTREAM FLOW STANDARDS IN THE CARIBBEAN BASIN
Sun, 07/24/2011 - 12:40 — ckassSCATENA, F. N. 2004. A SURVEY OF METHODS FOR SETTING MINIMUM INSTREAM FLOW STANDARDS IN THE CARIBBEAN BASIN.. River Res. Applic. 20: 127-135.
Abstract:
To evaluate the current status of instream flow practices in streams that drain into the Caribbean Basin, a voluntary survey of practising water resource managers was conducted. Responses were received from 70% of the potential continental countries, 100% of the islands in the Greater Antilles, and 56% of all the Caribbean island nations. Respondents identified effluent discharges, downstream water quality and existing extraction permits to be the most common sources of instream flow conflicts. In 75% of the countries, some type of formal procedures exist for reviewing permit applications for freshwater extraction. In 82% of the countries, effluent discharge permits state the amount of effluent that can be discharged into a water body while only 69% require that surface water extraction permits explicitly state the quantity of water that can be extracted. In setting instream flow requirements, record low flow is used over 83% of the time. Freshwater fish were identified as the most important aquatic organism but no country always considers the ecology or habitat requirements of aquatic species in their instream flow determinations and nearly 70% of the respondents indicated that multivariate, ecological-based methods are never used in their country. Survey responses also indicate there is a notable lack of public involvement during the issuing of water permits. Moreover, over 80% of the countries do not provide public announcements or hearings during the permit process. In summary, this survey indicates that while there is a widespread recognition of the need for instream flows, there is a general lack of regionally based information and public involvement regarding stream flow determination.
Lithological and fluvial controls on the geomorphology of tropical montane stream channels in Puerto Rico
Sun, 07/24/2011 - 12:36 — ckassPike, Andrew S.; Scatena, F.N.; Wohl, Ellen E. 2010. Lithological and fluvial controls on the geomorphology of tropical montane stream channels in Puerto Rico. Earth Surface Processes and Landforms. DOI: 10.1002/esp.1978.
Abstract:
An extensive survey and topographic analysis of fi ve watersheds draining the Luquillo Mountains in north-eastern Puerto Rico was conducted to decouple the relative infl uences of lithologic and hydraulic forces in shaping the morphology of tropical montane stream channels. The Luquillo Mountains are a steep landscape composed of volcaniclastic and igneous rocks that exert a localized lithologic infl uence on the stream channels. However, the stream channels also experience strong hydraulic forcing due to high unit discharge in the humid rainforest environment. GIS-based topographic analysis was used to examine channel profi les, and survey data were used to analyze downstream changes in channel geometry, grain sizes, stream power, and shear stresses. Results indicate that the longitudinal profi les are generally well graded but have concavities that refl ect the infl uence of multiple rock types and colluvial-alluvial transitions. Non-fl uvial processes, such as landslides, deliver coarse boulder-sized sediment to the channels and may locally determine channel gradient and geometry. Median grain size is strongly related to drainage area and slope, and coarsens in the headwaters before fi ning in the downstream reaches; a pattern associated with a mid-basin transition between colluvial and fluvial processes. Downstream hydraulic geometry relationships between discharge, width and velocity (although not depth) are well developed for all watersheds. Stream power displays a mid-basin maximum in all basins, although the ratio of stream power to coarse grain size (indicative of hydraulic forcing) increases downstream. Excess dimensionless shear stress at bankfull fl ow wavers around the threshold for sediment mobility of the median grain size, and does not vary systematically with bankfull discharge; a common characteristic in self-forming ‘threshold’ alluvial channels. The results suggest that although there is apparent bedrock and lithologic control on local reach-scale channel morphology, strong fluvial forces acting over time have been suffi cient to override boundary resistance and give rise to systematic basin-scale patterns.
Riparian indicators of flow frequency in a tropical montane stream network
Sun, 07/24/2011 - 12:34 — ckassPike, A. S., and Scatena, F. N., 2010, Riparian indicators of flow frequency in a tropical montane stream
network: Journal of Hydrology, v. 382, p. 72–87, doi:10.1016/j.jhydrol.2009.12.019.
Abstract:
Many field indicators have been used to approximate the magnitude and frequency of flows in a variety of
streams and rivers, yet due to a scarcity of long-term flow records in tropical mountain streams, little to
no work has been done to establish such relationships between field features and the flow regime in
these environments. Furthermore, the transition between the active channel of a river and the adjacent
flood zone (i.e. bankfull) is an important geomorphologic and ecological boundary, but is rarely identifiable
in steep mountain channels that lack alluvial flood plains. This study (a) quantifies relationships
between field indicators and flow frequency in alluvial and steepland channels in a tropical mountain
stream network and (b) identifies a reference active channel boundary in these channels, based on statistically
defined combinations of riparian features, that corresponds to the same flow frequency of the
bankfull stage and the effective discharge in adjacent alluvial channels. The relative elevation of transitions
in riparian vegetation, soil, and substrate characteristics were first surveyed at nine stream gages in
and around the Luquillo Experimental Forest in Northeastern Puerto Rico. The corresponding discharge,
flow frequency, and recurrence intervals associated with these features was then determined from longterm
15-min discharge records and a partial duration series analysis. Survey data indicate that mosses
and short grasses dominate at a stage often inundated by sub-effective flows. Herbaceous vegetation is
associated with intermediate discharges that correspond to the threshold for sediment mobilization.
Near-channel woody shrubs and trees establish at elevations along the channel margin inundated by a
less frequent discharge that is coincident with the effective discharge of bed load sediment transport.
Our data demonstrate that in alluvial channels in the study, both the bankfull stage (as marked by a flood
plain) and the channel-forming (effective) discharge are associated with the presence of fine-grained substrate
and soil, and tall, mature woody vegetation. In montane reaches that lack a flood plain, a boundary
that is characterized by the incipient presence of soil, woody shrubs, and trees corresponds to the same
flow frequency as the bankfull discharge of nearby alluvial channels. The reference discharge based on
these riparian features in steepland sites has an average exceedance probability between 0.09% and
0.30%, and a recurrence interval between 40 and 90 days. We conclude that flows with similar frequencies
influence the establishment of riparian vegetation, soil development, and substrate characteristics
along channel margins in similar ways. Thus, these riparian features can be used as an indicator of
hydrogeomorphic site conditions to identify active channel boundaries that occur at a constant flow frequency
throughout the study stream network.
Water Quality Trading in the Lower Delaware River Basin: A Resource for Practitioners
Sun, 07/24/2011 - 12:32 — ckassScatena, F. N., Curley, D., Laskowski, S., Abbot, K., Barkin, H., Shieh, W., and Johson, J. (2005). "Water Quality Trading in the Lower Delaware River Basin: A Resource for Practitioners." Institution of Environmental Studies, University of Pennsylvania, Philadelphia.
Abstract:
This document addresses technical and administrative issues related to the establishment of water quality trading (WQT) systems in the Lower Delaware River (LDR) Basin and is based on a series of workshops, public seminars, and analysis conducted in 2005. The report is designed for practitioners interested in developing WQT systems and provides a series of specific recommendations and steps to promote the development of WQT in the area.
Pollutant trading systems allow dischargers to obtain environmental protection in an economically-efficient manner by substituting, or trading, inexpensive controls at one location for expensive controls elsewhere. Although pollutant trading has been discussed for decades, there are few WQT systems operating in the United States and none have a long track record. Those that are in operation are limited in scope and were initiated by state, federal, or private funding. Nevertheless, WQT is expected to increase in the future and has already created incentives for dischargers to examine their operations and reduce their discharges beyond what the conventional methods would provide.
Instream-Flow Analysis for the Luquillo Experimental Forest, Puerto Rico: Methods and Analysis
Sun, 07/24/2011 - 12:17 — ckassScatena, F.N.; Johnson, S.L. 2001. Instream-Flow Analysis for the Luquillo Experimental Forest, Puerto Rico: Methods and Analysis. Gen. Tech. Rep. IITF-GTR-11. Rio Piedras, PR: U.S. Department of Agriculture, Forest Service, International Institute of Tropical Forestry. 30 p.
Abstract:
This study develops two habitat-based approaches for evaluating instream-flow requirements within the Luquillo Experimental Forest in northeastern Puerto Rico. The analysis is restricted to instream-flow requirements in upland streams dominated by the common communities of freshwater decapods.
In headwater streams, pool volume was the most consistent factor in predicting the abundance of common freshwater shrimp. In second- and third-order tributaries, both water depth and velocity can be used to define their habitats. The most common species of shrimp are reclusive during the day; at night they prefer areas of low velocity (<0.09 m/s) and areas shallower than 0.4 m. In headwater streams, total usable shrimp habitat declines rapidly when water depth in the deepest pools is less than 0.5 m. In second-and third-order tributaries, the amount of habitat declines rapidly when discharge is within one standard deviation of the average annual 7-day minimum flow. These dis-charges are typically exceeded between 95 and 99 percent of the time.
Analysis of habitat loss associated with different instream-flow constraints showed that habitat loss increases greatly when water extraction is equal to or greater than Q98. Among-reach differences in the amount of usable habitat resulting from differences in channel morphology can be as high as 35 percent. Therefore, site-specific studies should be conducted when using habitat-preference relations in a particular area.
Natural disturbances and the hydrology of humid tropical forests
Sun, 07/24/2011 - 12:14 — ckassScatena FN, Planos-Gutiérrez EO, Schellekens J. 2004. Natural disturbances
and the hydrology of humid tropical forests. In Forests,
Water, and People in the Humid Tropics, Bonell M, Bruijnzeel LA
(eds). Cambridge University Press: Cambridge; 5–28.
Abstract:
Humid tropical forests are highly dynamic ecosystems that are
affected by a wide array of environmental processes and disturbances
(Figure 19.1). Quantifying the magnitude, frequency, and
impacts of natural disturbances is essential for designing hydraulic
structures, developing water management strategies, and distinguishing
between natural variation and man-made influences.
A disturbance can be defined as any discrete event that transfers
mass and energy from one part of a system to another in a manner
that disrupts ecosystem, community, or population structure
and changes resource availability or the physical environment (see
White and Pickett 1985 for a detailed discussion). Natural disturbances
can be driven by both external factors – hurricanes, meteor
impacts, etc. – and the biological properties of the system such
as senescence, pathogens, etc. The natural disturbances specified
by the United Nations in the International Decade of Natural Disaster
Reduction were earthquakes, windstorms, tsunamis, floods,
landslides, volcanic eruptions, wildfires, grasshopper and locust
infestations, drought, and desertification (Board on Natural Disasters,
1999). Additional natural disturbances known to affect the
hydrology of humid tropical forests are tree falls, pathogens, exotic
invasions and meteor impacts.
Quantifying the effects of disturbances on landform morphology
and ecosystem development have been major themes in geomorphology
and ecology (Wolman and Miller, 1960, Connell,
1978). This approach has led to the paradigm that landscapes are
structured by the processes acting upon them (O’Neill et al., 1986,
Urban et al., 1987, Scatena, 1995). It is now generally recognised
that the ability of a disturbance to affect the morphology of a
landscape or the structure of an ecosystem depends on: (1) the type of disturbance (e.g., flood, fire, landslide, biologic, anthropogenic
etc.); (2) the force exerted (e.g. wind velocity and duration, rainfall
magnitude and intensity, earthquake magnitude etc.); (3) the
ecosystem component that is impacted directly (e.g. soil, biomass,
leaf area etc.); (4) the area affected and the spatial distribution of
impacts; (5) the return period or frequency of the event; (6) the
condition of the system at the time of the disturbance (e.g. structure,
regeneration phase, time since last disturbance); and (7) the
magnitude of the constructive or restorative processes that occur
between disturbances.
Hydrometeorology of tropical montane cloud forests: emerging patterns
Sun, 07/24/2011 - 12:06 — ckassBruijnzeel LA, Mulligan M, Scatena FN. 2010. Hydrometeorology of
tropical montane cloud forests: emerging patterns. Hydrological
Processes. DOI: 10.1002/hyp.7974.
Abstract:
altitudinal limits between which TMCF generally occur (800–3500 m.a.s.l. depending on mountain size and distance to coast)
their current areal extent is estimated at ¾215 000 km2 or 6Ð6% of all montane tropical forests. Alternatively, on the basis of
remotely sensed frequencies of cloud occurrence, fog-affected forest may occupy as much as 2Ð21 Mkm2. Four hydrologically
distinct montane forest types may be distinguished, viz. lower montane rain forest below the cloud belt (LMRF), tall lower
montane cloud forest (LMCF), upper montane cloud forest (UMCF) of intermediate stature and a group that combines stunted
sub-alpine cloud forest (SACF) and ‘elfin’ cloud forest (ECF). Average throughfall to precipitation ratios increase from
0Ð72 š 0Ð07 in LMRF (n D 15) to 0Ð81 š 0Ð11 in LMCF (n D 23), to 1Ð0 š 0Ð27 (n D 18) and 1Ð04 š 0Ð25 (n D 8) in UMCF
and SACF–ECF, respectively. Average stemflow fractions increase from LMRF to UMCF and ECF, whereas leaf area index
(LAI) and annual evapotranspiration (ET) decrease along the same sequence. Although the data sets for UMCF (n D 3) and
ECF (n D 2) are very limited, the ET from UMCF (783 š 112 mm) and ECF (547 š 25 mm) is distinctly lower than that
from LMCF (1188 š 239 mm, n D 9) and LMRF (1280 š 72 mm; n D 7). Field-measured annual ‘cloud-water’ interception
(CWI) totals determined with the wet-canopy water budget method (WCWB) vary widely between locations and range between
22 and 1990 mm (n D 15). Field measured values also tend to be much larger than modelled amounts of fog interception,
particularly at exposed sites. This is thought to reflect a combination of potential model limitations, a mismatch between the
scale at which the model was applied (1 ð 1 km) and the scale of the measurements (small plots), as well as the inclusion of
near-horizontal wind-driven precipitation in the WCWB-based estimate of CWI. Regional maps of modelled amounts of fog
interception across the tropics are presented, showing major spatial variability. Modelled contributions by CWI make up less
than 5% of total precipitation in wet areas to more than 75% in low-rainfall areas. Catchment water yields typically increase
from LMRF to UMCF and SACF–ECF reflecting concurrent increases in incident precipitation and decreases in evaporative
losses. The conversion of LMCF (or LMRF) to pasture likely results in substantial increases in water yield. Changes in
water yield after UMCF conversion are probably modest due to trade-offs between concurrent changes in ET and CWI.
General circulation model (GCM)-projected rates of climatic drying under SRES greenhouse gas scenarios to the year 2050
are considered to have a profound effect on TMCF hydrological functioning and ecology, although different GCMs produce
different and sometimes opposing results. Whilst there have been substantial increases in our understanding of the hydrological
processes operating in TMCF, additional research is needed to improve the quantification of occult precipitation inputs (CWI
and wind-driven precipitation), and to better understand the hydrological impacts of climate- and land-use change. Copyright
2010 John Wiley & Sons, Ltd.
