Subject: Force Main Friction Loss in InfoSWMM and the Transition from Partial to Full Flow
[as the full pipe friction loss method (see Figure 1 for the internal definition of full flow). A function called ForceMain in InfoSWMM whose purpose is to compute the Darcy-Weisbach friction factor for a force main using the Swamee and Jain approximation to the Colebrook-White equation . No matter which method you use for full flow the program will use Manning’s equation to calculate the loss in the link when the link is not full (see Figure 2 for the equations used for calculating the friction loss – variable dq1 in the St Venant equation for InfoSWMM). The regions for the different friction loss equations are shown in Figure 3.
There is no slot in InfoSWMM for the full pipe flow as a surcharged node in InfoSWMM uses this point iteration equation (Figure 4):
dY/dt = dQ / The sum of the Connecting Link values of dQ/dH
where Y is the depth in the node, dt is the time step, H is the head across the link (downstream – upstream), dQ is the net inflow into the node and dQ/dH is the derivative with respect to H of the link St Venant equation. If you are trying to calibrate the surcharged node depth, the main calibration variables are the time step and the link roughness:
1. Mannings’s N
2. Hazen-Williams or
3. Darcy-Weisbach
The link roughness is part of the term dq1 in the St Venant solution and the other loss terms are included in the term dq5. You can adjust the roughness of the surcharged link to affect the node surcharge depth. The point iteration continues until the sum of the flow in the node is zero – basically the new depth in the node either increases or decreases the friction loss in the force main so that net flow at the node is zero. This is why it is important to use the right time step to ensure that the net flow is zero when the pumps turn on and off.
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Figure 1. How the full pipe condition is defined in InfoSWMM - both ends have to be full |
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Figure 2: Friction equations used in SWMM 5 for a Force Main.
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Figure 4. The Node Surcharge Equation is a function of the net inflow and the sum of the term dQ/dH in all connecting links. Generally, as you increase the roughness the value of dQ/dH increases and the denominator of the term dY/dt = dQ/dQdH increases.
You can model Force Mains in SWMM 5 using either Darcy Weisbach or Hazen Williams as the full pipe friction loss method (see Figure 1 for the internal defintion of full flow). No matter which method you use for full flow the program will use Manning’s equation to calculate the loss in the link when the link is not full (see Figure 2 for the equations used for calculating the friction loss – variable dq1 in SWMM 5). Force Main Friction Loss in SWMM 5.
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Figure 1. How the full pipe condition is defined in SWMM 5 |
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Figure 2: Friction equations used in SWMM 5 for a Force Main.
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Subject: Example DUPUIT-FORCHHEIMER APPROXIMATION FOR SUBSURFACE FLOW Model in SWMM 5
This example was created from an older SWMM 4 model from 1988 using the SWMM 4 to SWMM 5 converter. The values for the coefficients in this case are A1 = A3 = 4*K/L^2, A2 = 0, B1 or the exponent or B1=2 or from Appendix X in the SWMM 4 manual from OSU (http://eng.odu.edu/cee/resources/model/mbin/swmm/swmm_6.pdf)
Subject: Example Groundwater Model in SWMM 5
The attached model shows three ways in which the groundwater model of the SWMM 5 subcatchments interact with the node depths of the hydraulic network. The hydraulic network interaction can be either:
1. At a fixed water surface elevation,
2. At a time varying water surface elevation based on the inflow and geometry of the node and
3. At a threshold node water surface elevation.
Subject: Example SWMM 5 Snowmelt Model
Attached is a simple sample snowmelt model in SWMM 5 that has built in snowfall and temperature in a one subcatcment model with snowmelt. You define the separation of precipitation into snowfall and rainfall by setting a base temperature in the Snow Pack Editor. The precipitation that falls with when the air temperature is below the base temperature is stored in a snow pack where it eventually will melt when the temperature rises or is moved via plowing. You can have an initial snow cover, final snow cover and runoff from the melting snow long after the snowfall occurs.
Subject: My History with Various Versions of SWMM: SWMM3, SWMM4, SWMM5, XP-SWMM and InfoSWMM
I first learned about SWMM in a brochure from the University of Florida when I was just a 17 year old senior in High School. Water resources and the description of SWMM seemed to be worthy career goals at the time and I have been extremely lucky to have the opportunity to work and develop many SWMM related products in my working life. I am especially proud that SWMM 3, SWMM 4 and SWMM 5 are both public domain and open source software. You can open up and look at the code and add features and internal tests on your own. You can customize the input and output of SWMM 5 if you want to but most importantly you have direct access to the source code so you can verify the computational algorithms.
InfoSWMM is an Arc GIS extension that works in Arc Map but we at Innovyze are proud that we have superb import and export features to SWMM 5 from Arc Map and use the SWMM 5 engine as our engine solution. You can look at the internal workings of the InfoSWMM engine by downloading the current SWMM 5 C code from the EPA website http://www.epa.gov/nrmrl/wswrd/wq/models/swmm/ InfoSWMM also has all of the Arc GIS programming tools, Python programming, editing and drawing features and Table of Contents attribute features to make a better model but that model will still use the open source SWMM 5 engine inside of InfoSWMM. When you use InfoSWMM you are using the SWMM 5 engine but with many extra input and output features to help prepare the data for the current SWMM 5 engine and analyze the SWMM 5 engine output in maps, tables and graphs.
Best Regards,
Robert Dickinson
Subject: Runoff Routing Options Example in SWMM 5
There are six options for runoff routing in SWMM 5:
· All Runoff to an Outlet Node
· All Runoff to another Subcatchment
· All Runoff to the Pervious Area of the Subcatchment or other Subcatchment
· All Runoff to the Impervious Area of the Subcatchment or other Subcatchment
· Partial Runoff to the Pervious Area of the Subcatchment or other Subcatchment
· Partial Runoff to the Impervious Area of the Subcatchment or other Subcatchment
The attached example SWMM 5.0.022 file has three catchments in a chain, the 1st Subcatchment Routes to the Pervious area of the 2nd Subcatchment and the 2nd Subcatchment routes the runoff to the Impervious area of the 3rd Subcatchment which routes all runoff to an outlet node.
Subject: Example FM SWMM 5 model with and without Surcharge Depth
You need to use the surcharge depth for a Force Main in SWMM 5 to allow the engine to find the right point on the pump curve and pump up the rising main. If you do not use a surcharge depth then the flow MAY be very small in the rising main due to a small head difference. Of course the flow in the force main depends on the pump curve you have entered but having the right downstream head of depth for the link matter as well. The attached model was created in SWMM 5.0.022
Subject: How to Edit the Subcatchment Polygons in InfoSWMM with Arc Map
You can edit the polygon boundaries of the Subcatchments in Arc GIS by using the Editor command and either editing the vertices or by using the Reshape Feature Tool to adjust the boundaries or snap to the polygon lines or vertex points. You should start the editing session by right mouse clickining on the Subcatchment Feature layer
Vertex Editing and Reshape Feature Tool
Subject: Average Residence time in InfoSWMM and H2OMAP SWMM
Here is one way to estimate the residence time:
1. Plot the System Outflow and Storage in the InfoSWMM Report Manager
2. Click on the Report Button and copy the Outflow and Storage Time Series
3. Paste to Excel
4. Calculate the Residence time as Storage / Outflow and Graph
5. You will have an understanding of the residence time in your network
6. If you have a dry weather flow then a hot start file will give a better estimate at the start of the simulation
Dr. Paul F. Boulos Named Distinguished Diplomate in Navigation Engineering by the ASCE Academy of Coastal, Ocean, Port & Navigation Engineers
Innovyze President Receives ACOPNE’s Highest Honor
Broomfield, Colorado USA, April 24, 2012 — The Board of Trustees of the Academy of Coastal, Ocean, Port & Navigation Engineers (ACOPNE) has awarded Innovyze President Dr. Paul F. Boulos Distinguished Diplomate status in Navigation Engineering (Dist.D.NE), the academy’s highest honor. As a recipient of this award, Dr. Boulos joins an elite group of 23 diplomates worldwide with this distinction. Dr. Boulos will be presented this signal award at a special induction ceremony and reception to be held during the Dredging 2012 conference in San Diego, California, October 22-25. ACOPNE is an affiliate of the American Society of Civil Engineers (ASCE). Dredging 2012 is a four-day technical specialty conference organized by PIANC USA and the Coasts, Oceans, Ports and Rivers Institute of American Society of Civil Engineers (COPRI ASCE).
Dr. Boulos is one of the world’s foremost experts on water resources and navigation engineering. He has won numerous industry honors, including notable technical awards from ASCE, the American Water Works Association and the U.S. Environmental Protection Agency, and was inducted into the University of Kentucky College of Engineering Hall of Distinction, the most prestigious honor given by the university to its alumni. His publications include nine authoritative books and more than 100 scholarly papers. He is a Fellow of the American Society of Civil Engineers (F.ASCE), a Board Certified Environmental Engineer (by eminence) of the American Academy of Environmental Engineers (BCEEM), and an Honorary Diplomate of Water Resources Engineering (Hon.D.WRE) of the American Academy of Water Resources Engineers (AAWRE), the academy’s highest honor. He graduated with a Bachelor of Science degree in General Science from the Lebanese American University (Beirut, Lebanon) and was named the university’s 2008 Alumnus of the Year for his extraordinary professional achievement. Dr. Boulos also received a Doctorate, Master of Science and Bachelor of Science with distinction in Civil Engineering from the University of Kentucky in Lexington and has completed the Advanced Management Program at Harvard Business School.
“I am deeply humbled and honored to be selected for this distinguished award,” said Boulos. “I am so proud to be a part of this noble and great profession and to be able to contribute to its advancement. It’s truly a privilege to receive such special recognition for doing something I deeply love and enjoy — especially when it comes from the men and women I most admire.”
Diplomate status credential recognizes an advanced expertise in the practice of Coastal, Ocean, Port & Navigation Engineering (COPNE). Navigation engineering involves the life cycle planning, design, construction, operation and life maintenance of safe, secure, reliable, efficient and environmentally sustainable navigable waterways (channels, structures and support systems) used to move people and goods by waterborne vessels. Distinguished Diplomate status, ACOPNE’s highest honor, is awarded exclusively to those who have made significant contributions to the COPNE profession. To date, only 23 engineers and practitioners worldwide (eight in navigation engineering) have earned this distinction, a tribute to their exceptional technical and professional leadership within the COPNE community.
“We are proud to honor Dr. Boulos for his eminence, commitment and exceptional contributions to the profession,” said Michael A. Ports, PE, PH, D.WRE, D.NE, BCEE, Principal of Ports Engineering in Jacksonville, Florida, and President of ACOPNE. “He has distinguished himself professionally amongst his peers and demonstrates the characteristics of a role model to his fellow engineers and to the members of the community. We thank and congratulate him for his lifetime of achievements, tireless efforts, and advocacy for the advancement of research and best practices in navigation engineering.”
For more information on ACOPNE, visit www.acopne.org.
About Innovyze
Innovyze is a leading global provider of wet infrastructure business analytics software solutions designed to meet the technological needs of water and wastewater utilities, government industries, and engineering organizations worldwide. Its clients include the majority of the largest UK, Australasian, East Asian and North American cities, foremost utilities on all five continents, and ENR top-rated design firms. With unparalleled expertise and offices in North America, Europe, and Asia Pacific, the Innovyze connected portfolio of best-in-class product lines empowers thousands of engineers to competitively plan, manage, design, protect, operate and sustain highly efficient and reliable infrastructure systems, and provides an enduring platform for customer success. For more information, call Innovyze at +1 626-568-6868, or visit www.innovyze.com.
Scientists say the notoriously dry continent of Africa is sitting on a vast reservoir of groundwater.
They argue that the total volume of water in aquifers underground is 100 times the amount found on the surface.
The team have produced the most detailed map yet of the scale and potential of this hidden resource.
Writing in the journal Environmental Research Letters, they stress that large scale drilling might not be the best way of increasing water supplies.
Across Africa more than 300 million people are said not to have access to safe drinking water.
Demand for water is set to grow markedly in coming decades due to population growth and the need for irrigation to grow crops.
Freshwater rivers and lakes are subject to seasonal floods and droughts that can limit their availability for people and for agriculture. At present only 5% of arable land is irrigated.
When water falls as rain or snow, much of it either flows into rivers or is used to provide moisture to plants and crops. What is left over trickles down to the layers of rock that sit beneath the soil.
And just like a giant sponge, this ground water is held in the spaces between the rocks and in the tiny inter-connected spaces between individual grains in a rock like sandstone.
These bodies of wet rock are referred to as aquifers. Ground water does not sit still in the aquifer but is pushed and pulled by gravity and the weight of water above it.
The movement of the water through the aquifer removes many impurities and it is often cleaner than water on the surface.
Now scientists have for the first time been able to carry out a continent-wide analysis of the water that is hidden under the surface in aquifers. Researchers from the British Geological Survey and University College London (UCL) have mapped in detail the amount and potential yield of this groundwater resource across the continent.
Helen Bonsor from the BGS is one of the authors of the paper. She says that up until now groundwater was out of sight and out of mind. She hopes the new maps will open people's eyes to the potential.
"Where there's greatest ground water storage is in northern Africa, in the large sedimentary basins, in Libya, Algeria and Chad," she said.
"The amount of storage in those basins is equivalent to 75m thickness of water across that area - it's a huge amount."
Ancient events
Due to changes in climate that have turned the Sahara into a desert over centuries many of the aquifers underneath were last filled with water over 5,000 years ago.
The scientists collated their information from existing hydro-geological maps from national governments as well as 283 aquifer studies.
The researchers say their new maps indicate that many countries currently designated as "water scarce" have substantial groundwater reserves.
However, the scientists are cautious about the best way of accessing these hidden resources. They suggest that widespread drilling of large boreholes might not work.
Dr Alan MacDonald of the BGS, lead author of the study, told the BBC: "High-yielding boreholes should not be developed without a thorough understanding of the local groundwater conditions.
"Appropriately sited and developed boreholes for low yielding rural water supply and hand pumps are likely to be successful."
With many aquifers not being filled due to a lack of rain, the scientists are worried that large-scale borehole developments could rapidly deplete the resource.
African water supplies may be more resilient to climate change than was thoughtAccording to Helen Bonsor, sometimes the slower means of extraction can be more efficient.
"Much lower storage aquifers are present across much of sub-Saharan Africa," she explained.
"However, our work shows that with careful exploring and construction, there is sufficient groundwater under Africa to support low yielding water supplies for drinking and community irrigation."
The scientists say that there are sufficient reserves to be able to cope with the vagaries of climate change.
"Even in the lowest storage aquifers in semi arid areas with currently very little rainfall, ground water is indicated to have a residence time in the ground of 20 to 70 years." Dr Bonsor said.
"So at present extraction rates for drinking and small scale irrigation for agriculture groundwater will provide and will continue to provide a buffer to climate variability."
The publication of the new map was welcomed by the UK's secretary of state for international development, Andrew Mitchell.
"This is an important discovery," he said. "This research, which the British Government has funded, could have a profound effect on some of the world's poorest people, helping them become less vulnerable to drought and to adapt to the impact of climate change."
Topic: Sam Shamsi and swmm-online-com
Sam as an interesting blog or web page with other GIS and SWMM links including his well known annual Top 10 list about various Stormwater modeling subjects. The link is
http://sites.google.com/site/shamsigisapplications/3-my-web-sites/swmm-online-com
InfoSWMM 2D Version 5.0 Delivers New Level of Surface Mesh Automation and Faster,
Higher-Fidelity Simulation Results
Latest Release Solidifies Product as Leading GIS-centric Urban Drainage Modeling and Management Solution
Broomfield, Colorado USA, April 17, 2012 — Innovyze, a leading global innovator of business analytics software and technologies for wet infrastructure, today announced the worldwide availability of the V5.0 Generation of its industry-leading InfoSWMM 2D for ArcGIS (Esri, Redlands, CA). InfoSWMM 2D delivers new ways to quickly and accurately build and analyze large and comprehensive two-dimensional (2D) models that reliably simulate urban stormwater, sanitary sewers, river flooding and pollutant transport. Users can accurately predict the extent and duration of urban and rural flooding, giving them comprehensive stormwater management directly within the powerful ArcGIS environment.
A fully hydrodynamic geospatial stormwater modeling and management software application, InfoSWMM 2D can model the entire land phase of the hydrologic cycle as applied to urban stormwater systems. The model can perform single-event or long-term (continuous) rainfall/runoff simulations accounting for climate, soil, land use, and topographic conditions of the watershed. In addition to simulating runoff quantity, InfoSWMM 2D can reliably predict runoff quality, including buildup and washoff of pollutants from primarily urban watersheds. It also features sophisticated Real-Time Control (RTC) schemes for the operational control and management of hydraulic structures.
Built atop ArcGIS and using exceptionally robust and efficient numerical simulation capabilities, InfoSWMM 2D seamlessly integrates advanced 1D and 2D functionalities into one environment. Users can model the most complex storm and combined sewer collection systems and surface flooding with incredible ease and accuracy.
When overland flows are routed through a complex urban area or highly varied terrain, the numerous elevation changes and obstacles can significantly impact modeling results. This problem can be further complicated by the presence of sewer networks, where flows can both enter and exit the system during flood events. With InfoSWMM 2D, users can employ 1D simulation to identify the location of flooding and 2D simulation to investigate the direction and depth of flood flows in specific areas.
The full 2D free-surface shallow water equations are solved using a highly advanced finite volume method. This is particularly suitable for rapidly varying flood flows, such as those through steep streets and road junctions, as well as bank overtopping or breaching. The unparalleled 1D/2D dynamic linking capabilities of InfoSWMM 2D give engineers the unprecedented power to analyze and predict potential flood extents, as well as depth and velocity. Engineers can also accurately model the interaction of surface and underground systems in an integrated 1D/2D environment. The software can simulate point sources, 2D boundaries, and multiple 2D mesh and simulation polygons in a sewer or stormwater network. Even better, the combined water level and velocity results throughout the flooded areas can be viewed as various comprehensive graphs, tables or even animated thematic flood maps.
Version 5.0 delivers new benefits in three major areas: (1) Higher productivity via a new fully automated surface mesh generation scheme and log file; (2) Greater fidelity via an improved surface mesh solver that can automatically detect and correct many types of problems, including duplicate vertices and segments, overlapping segments and crossing of 2D elements with 2D boundaries; and (3) Performance modeling with significantly greater computational speed.
“We’re deeply committed to providing a geospatial modeling experience that is both intuitive and powerful, and InfoSWMM 2D V5.0 embodies that commitment,” said Paul F. Boulos, Ph.D., BCEEM, Hon.D.WRE, F.ASCE, President and Chief Operating Officer of Innovyze. “This release delivers major geotechnological and computational enhancements in a short release cycle to make sure our customers are always equipped with the ultimate ArcGIS-centric decision support tool for stormwater and urban drainage systems. It greatly extends the core features of InfoSWMM, providing the most powerful and comprehensive ArcGIS-centric toolkit ever for managing the risks of urban and rural flooding.”
Subject: The Pump summary table of SWMM5.0.022 and the Percent Time off Columns
The pump summary table at the end of the SWMM 5 report file has two columns for the time off the pump curve BUT the two columns are only informative if the pump is a type 4 pump. If the pump type is 1, 2 or 3 then the low column is always 0 and when the volume, depth or head is either below the lowest point in the point curve or above the highest point in the pump curve the pump summary table lists the time off either low or high in the High column.
xMin is the 1st point in the pump curve for either volume, depth, head or depth, respectively for pump1, pump2, pump3 and pump4 type pumps
xMax is the last point in the pump curve for either volume, depth, head or depth, respectively for pump1, pump2, pump3 and pump4 type pumps
Florida Utility Chooses InfoSWMM for Smart GIS-Centric Stormwater Modeling
New Innovyze Customer, Fort Walton Beach Looks to ArcGIS-Centric Solutions to Model Its Complex Stormwater System
Broomfield, Colorado USA, April 10, 2012 — Innovyze, a leading global innovator of business analytics software and technologies for wet infrastructure, today announced that Fort Walton Beach, FL, has selected industry-leading InfoSWMM to meet its stormwater network modeling requirements. The purchase gives Fort Walton Beach access to the most advanced and comprehensive ArcGIS (Esri – Redlands, CA) integrated stormwater modeling and management applications in the industry.
The Fort Walton Beach Engineering & Utility Services Department manages multiple divisions within the City, including: Water Operations, Sewer Operations, Water Distribution, Sewer Collections, Stormwater Management, and Environmental Programs. The Stormwater Management group maintains thirty-five (35) miles of storm drains, eleven (11) retention ponds, and over 1,300 curb and surface inlets. The division also utilizes closed circuit television (CCTV) inspection techniques to inspect and maintain its stormwater system. “Adopting leading technology to optimize our system design and operation is critical to long term asset performance optimization,” said Engineering & Utility Services Director, Michael Beedie, P.E. “InfoSWMM does the best job of leveraging our existing GIS data and providing us with the unique combination of advanced hydraulic and hydrologic computations and ease-of-use.”
InfoSWMM reflects Innovyze’s ongoing commitment to delivering pioneering technology for the stormwater and wastewater industry. The full-featured InfoSWMM urban drainage network analysis and design program delivers unprecedented engineering productivity and is the only urban drainage modeling solution certified by the National Association of GIS-Centric Software (www.nagcs.com). It addresses all operations of a typical stormwater system — from analysis and design to management functions such as water quality assessment, pollution prediction, sediment transport, urban flooding, real-time control and record keeping — in a single, fully integrated geoengineering environment. The USEPA endorsed InfoSWMM’s powerful hydraulic computational engine and FEMA certified it.
Thanks to Innovyze’s responsive customer service, InfoSWMM continues to rapidly evolve with customers’ needs and is easier to use than ever before. The advanced technology behind the latest version includes scores of new, advanced features that make it easier, faster and less costly for organizations to develop better designs and operational improvements. These enhancements include easier transition between node surcharging and node flooding, stronger model validation that doesn’t interrupt simulation runs, greater RDII data compatibility, infiltration changes that allow the SWMM engine to behave more like TR-55 and TR-20, and the addition of default concentration for dry weather flow pollutants to enable more accurate water quality analysis.
“Fort Walton Beach has a complex stormwater system, requiring superior software tools to quickly and accurately build and analyze their hydraulic network models,” said Americas Operations Director J. Erick Heath, P.E. “InfoSWMM is a proven choice for utilities with these types of systems, enabling them to effectively design, operate and sustain safe and reliable drainage systems.”
Subject: Dual Drainage in SWMM 5
The purpose of the Dual Drainage tool in InfoSWMM is to create a major or street drainage network on top of an existing pipe or what is called the minor network in dual drainage. The created major network has a node (sometimes called the inlet node) on top of the existing minor network node connected by two OUTLET links. One outlet link takes the flow from the street and passes it to the minor network node, the second outlet link takes the surcharged minor network flow and passes it to the major network or street – the direction of flow is important (Figure 1). The general purpose of the Captured OUTLET is to use a head or depth equation to separate the street incoming flow into captured flow and bypass flow
Figure 1. Dual Drainage in General
Figure 2. How it looks in SWMM 5 with node, outlet and conduit elements.
Subject: Dual Drainage in SWMM 5
The purpose of the Dual Drainage tool in InfoSWMM is to create a major or street drainage network on top of an existing pipe or what is called the minor network in dual drainage. The created major network has a node (sometimes called the inlet node) on top of the existing minor network node connected by two OUTLET links. One outlet link takes the flow from the street and passes it to the minor network node, the second outlet link takes the surcharged minor network flow and passes it to the major network or street – the direction of flow is important (Figure 1). The general purpose of the Captured OUTLET is to use a head or depth equation to separate the street incoming flow into captured flow and bypass flow
Figure 1. Dual Drainage in General
Figure 2. How it looks in SWMM 5 with node, outlet and conduit elements.
Topic: Example Dual Drainage SWMM 5 model
Subject: How to Make a SWMM 5 Calibration File from InfoSWMM
1st Step: Graph a Link in InfoSWMM using the Date /Time Format
2nd Step: Click on the Report Button and copy the 1st two columns of data
3rd Step: Save the copied columns to a data file, replace the semi colon and add the name of the link to the top of the data file as shown below
4th Step: Connect the created calibration data file t o the SWMM 5 Calibration Data Link Flow Rate
5th Step: Run the Simulation and you should see two graphs on the screen for the designated link
Hello,
In the STORM WATER MANAGEMENT MODEL QUALITY ASSURANCE REPORT: Dynamic Wave Flow Routing, the momentum equation is written as:
I don't know why the term for the "Bed Slope" is left out in this equation, as it is the friction slope and the local losses taken care of.
Any information on why this term is left out would be helpful.
Thanks in Advance.
One key to this understanding lies in the core monsoon zone (CMZ) – a region in the central part of India that is a very sensitive indicator of the monsoon throughout the India peninsula.
“If you know what’s happening there, you know more or less what’s happening in the rest of India,” said Camilo Ponton, a student in the MIT-WHOI Joint Program in Oceanography and lead author of the study recently published in Geophysical Research Lettersentitled "Holocene Aridification of India". “Our biggest problem has been a lack of evidence from this region to extend the short, existing records.”
The study was designed by WHOI geologist Liviu Giosan and geochemist Tim Eglinton, now at ETH in Zurich, and makes use of a sediment core collected by the National Gas Hydrate Program of India in 2006. Sailing around India aboard the drilling vessel JOIDES Resolution for several months, Giosan enlisted colleagues from India and US to help with the project. Extracted from a “sweet spot” in the Bay of Bengal where the Godavari River drains the central Indian peninsula and over which monsoon winds carry most of the precipitation, the core has provided the basis for a 10,000-year reconstruction of climate in the Indian peninsula’s CMZ .
“We are fortunate to have this core from close to the river mouth, where it accumulates sediment very fast,” said Ponton. “Every centimeter of sediment contains 10 to 20 years’ worth of information. So it gives us the advantage of high temporal resolution to address the problems.”
When put together, the research tells the story of growing aridity in India, enables valuable insights into the impact of the monsoon on past cultures, and points scientists toward a way to model future monsoons.
To assemble the 10,000-year record, the team looked to both what the land and the ocean could tell them. Contained within the sediment core’s layers are microscopic compounds from the trees, grasses, and shrubs that lived in the region and remnants of plankton fossils from the ocean.
“The geochemical analyses of the leaf waxes tell a simple story,” said Giosan. “About 10,000 years ago to about 4500 ago, the Godavari River drained mostly terrain that had humidity-loving plants. Stepwise changes starting at around 4,000 years ago and again after 1,700 years ago changed the flora toward aridity-adapted plants. That tells us that central India – the core monsoon zone – became drier.”
Analyses of the plankton fossils support the story reconstructed from plant remains and reveal a record of unprecedented spikes and troughs in the Bay of Bengal’s salinity – becoming saltier during drought periods and fresher when water from the monsoon filled the river and rained into the Bay. Similar drought periods have been documented in shorter records from tree rings and cave stalagmites within India lending further support to this interpretation.
With a picture emerging of changes in the ancient flora of India, Giosan tapped archaeobotanist Dorian Fuller’s interest.
“What the new paleo-climatic information makes clear is that the shift towards more arid conditions around 4,000 years ago corresponds to the time when agricultural populations expanded and settled village life began,” says Fuller of the Institute of Archaeology, University College London. “Arid-adapted food production is an old cultural tradition in the region, with cultivation of drought-tolerant millets and soil-restoring bean species. There may be lessons to learn here, as these drought-tolerant agricultural traditions have eroded over the past century, with shift towards more water and chemical intensive forms of modern agriculture.”
Together, the geological record and the archaeological evidence tell a story of the possible fate of India’s earliest civilizations. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ~4,000 years. In the already dry Indus basin, the urban Harappan civilization failed to adapt to even harsher conditions and slowly collapsed. But aridity favored an increase in sophistication in the central and south India where tropical forest decreased in extent and people began to settle and do more agriculture. Human resourcefulness proved again crucial in the rapid proliferation of rain-collecting water tanks across the Indian peninsula, just as the long series of droughts settled in over the last 1,700 years.
What can this record tell us about future Indian monsoons? According to Ponton, “How the monsoon will behave in the future is highly controversial. Our research provides clues for modeling and that could help determine whether the monsoon will increase or decrease with global warming.”
The study found that the type of monsoon and its droughts are a function of the Northern Hemisphere’s incoming solar radiation – or “insolation.” Every year, the band of heavy rain known as the Inter-Tropical Convergence Zone, or ITCZ, moves north over India.
“We found that when the Asian continent is least heated by the sun, the northward movement of the rain appears to hesitate between the Equator and Asia, bringing less rain to the north,” said Giosan. “The fact that long droughts have not occurred over the last 100 years or so, as humans started to heat up the planet, but did occur earlier, suggest that we changed the entire monsoon game, and may have inadvertently made it more stable!”
Story Source:
The above story is reprinted from materials provided byWoods Hole Oceanographic Institution.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
Map of the Indian peninsula, showing where the monsoon winds blow (white arrows) and how the salinity (white lines) is lower in Bay of Bengal due to monsoon rain over the Bay and rivers draining into the it. (The black arrow represents non-monsoon wind.) The study's sediment core (red dot) was extracted from a “sweet spot” in the Bay of Bengal where the Godavari River drains the central Indian peninsula and over which monsoon winds carry the most precipitation. (Credit: Courtesy of C. Ponton and L. Giosan)
